How do I generate random integers within a specific range in Java

Question

How do I generate a random int value in a specific range  I have tried the following  but those do not work  Attempt 1  randomNum   minimum    int  Math random     maximum    Bug  randomNum can be bigger than maximum  Attempt 2  Random rn   new Random    int n   maximum - minimum   1  int i   rn nextInt     n  randomNum    minimum   i   Bug  randomNum can be smaller than minimum

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rand nextInt  max 1  - min    min    This is working fine

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This methods might be convenient to use   This method will return a random number between the provided min and max value   public static int getRandomNumberBetween int min  int max        Random foo   new Random        int randomNumber   foo nextInt max - min    min      if  randomNumber    min               Since the random number is between the min and max values  simply add 1         return min   1        else           return randomNumber            and this method will return a random number from the provided min and max value  so the generated number could also be the min or max number    public static int getRandomNumberFrom int min  int max        Random foo   new Random        int randomNumber   foo nextInt  max   1  - min    min       return randomNumber

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public static void main String   args         Random ran   new Random         int min  max      Scanner sc   new Scanner System in       System out println  Enter min range         min   sc nextInt        System out println  Enter max range         max   sc nextInt        int num   ran nextInt min       int num1   ran nextInt max       System out println  Random Number between given range is     num1

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rand nextInt  max 1  - min    min

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To generate a random number  in between two numbers   use the following code   Random r   new Random    int lowerBound   1  int upperBound   11  int result   r nextInt upperBound-lowerBound    lowerBound    This gives you a random number in between 1  inclusive  and 11  exclusive   so initialize the upperBound value by adding 1  For example  if you want to generate random number between 1 to 10 then initialize the upperBound number with 11 instead of 10

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It s better to use SecureRandom rather than just Random   public static int generateRandomInteger int min  int max        SecureRandom rand   new SecureRandom        rand setSeed new Date   getTime         int randomNum   rand nextInt  max - min    1    min      return randomNum

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Following code could be used   ThreadLocalRandom current   nextInt rangeStart  rangeEndExclusive

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import java util Random    public class RandomUtil          Declare as class variable so that it is not re-seeded every call     private static Random random   new Random                    Returns a psuedo-random number between min and max  both inclusive          param min Minimim value         param max Maximim value  Must be greater than min          return Integer between min and max  both inclusive          see java util Random nextInt int              public static int nextInt int min  int max               nextInt is normally exclusive of the top value             so add 1 to make it inclusive         return random nextInt  max - min    1    min

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Forgive me for being fastidious  but the solution suggested by the majority  i e   min   rng nextInt max - min   1    seems perilous due to the fact that    rng nextInt n  cannot reach Integer MAX VALUE   max - min  may cause overflow when min is negative    A foolproof solution would return correct results for any min  lt   max within  Integer MIN VALUE  Integer MAX VALUE   Consider the following naive implementation   int nextIntInRange int min  int max  Random rng       if  min  gt  max          throw new IllegalArgumentException  Cannot draw random int from invalid range      min          max                  int diff   max - min     if  diff  gt   0  amp  amp  diff    Integer MAX VALUE          return  min   rng nextInt diff   1            int i     do         i   rng nextInt         while  i  lt  min    i  gt  max      return i      Although inefficient  note that the probability of success in the while loop will always be 50  or higher

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The following is another example using Random and forEach  int firstNum   20   Inclusive int lastNum   50   Exclusive int streamSize   10  Random num   new Random   ints 10  20  50  forEach System out  println

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Let us take an example   Suppose I wish to generate a number between 5-10   int max   10  int min   5  int diff   max - min  Random rn   new Random    int i   rn nextInt diff   1   i    min  System out print  The Random Number is     i     Let us understand this             Initialize max with highest value and min with the lowest value            Now  we need to determine how many possible values can be obtained  For this example  it would be                  5  6  7  8  9  10               So  count of this would be max - min   1                   i e  10 - 5   1   6               The random number will generate a number between 0-5                   i e  0  1  2  3  4  5               Adding the min value to the random number would produce                  5  6  7  8  9  10                     Hence we obtain the desired range

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import java util Random   public class RandomSSNTest        public static void main String args              generateDummySSNNumber                  831-33-6049     public static void generateDummySSNNumber             Random random   new Random             int id1   random nextInt 1000    3         int id2   random nextInt 100    2         int id3   random nextInt 10000    4          System out print  id1  -  id2  -  id3               You can also use   import java util concurrent ThreadLocalRandom  Random random   ThreadLocalRandom current      However  this class doesn   t perform well in a multi-threaded environment

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You can achieve that concisely in Java 8   Random random   new Random     int max   10  int min   5  int totalNumber   10   IntStream stream   random ints totalNumber  min  max   stream forEach System out  println

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To generate a random number  in between two numbers   use the following code   Random r   new Random    int lowerBound   1  int upperBound   11  int result   r nextInt upperBound-lowerBound    lowerBound    This gives you a random number in between 1  inclusive  and 11  exclusive   so initialize the upperBound value by adding 1  For example  if you want to generate random number between 1 to 10 then initialize the upperBound number with 11 instead of 10

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You can use following way to do that int range   10  int min   5 Random r   new Random    int    r nextInt range    min

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Use   Random ran   new Random    int x   ran nextInt 6    5    The integer x is now the random number that has a possible outcome of 5-10

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I just generate a random number using Math random   and multiply it by a big number  let s say 10000   So  I get a number between 0 to 10 000 and call this number i  Now  if I need numbers between  x  y   then do the following   i   x    i    y - x      So  all i s are numbers between x and y   To remove the bias as pointed out in the comments  rather than multiplying it by 10000  or the big number   multiply it by  y-x

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The following is another example using Random and forEach  int firstNum   20   Inclusive int lastNum   50   Exclusive int streamSize   10  Random num   new Random   ints 10  20  50  forEach System out  println

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rand nextInt  max 1  - min    min

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The following snippet will give a random value between 0 and 10000   import java util Random  public class Main       public static void main String   args            Random rand   new Random            System out printf   04d n   rand nextInt 10000

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Another option is just using Apache Commons    import org apache commons math random RandomData  import org apache commons math random RandomDataImpl   public void method         RandomData randomData   new RandomDataImpl        int number   randomData nextInt 5  10

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Following code could be used   ThreadLocalRandom current   nextInt rangeStart  rangeEndExclusive

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int func int max  int min          int range   max - min   1                  Math random   function will return a random no between  0 0 1 0         int res    int    Math random   range  min         return res

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public static void main String   args         Random ran   new Random         int min  max      Scanner sc   new Scanner System in       System out println  Enter min range         min   sc nextInt        System out println  Enter max range         max   sc nextInt        int num   ran nextInt min       int num1   ran nextInt max       System out println  Random Number between given range is     num1

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There is a library at https   sourceforge net projects stochunit  for handling selection of ranges   StochIntegerSelector randomIntegerSelector   new StochIntegerSelector    randomIntegerSelector setMin -1   randomIntegerSelector setMax 1   Integer selectInteger   randomIntegerSelector selectInteger      It has edge inclusion preclusion

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In Java 1 7 or later  the standard way to do this is as follows   import java util concurrent ThreadLocalRandom      nextInt is normally exclusive of the top value     so add 1 to make it inclusive int randomNum   ThreadLocalRandom current   nextInt min  max   1     See the relevant JavaDoc   This approach has the advantage of not needing to explicitly initialize a java util Random instance  which can be a source of confusion and error if used inappropriately   However  conversely there is no way to explicitly set the seed so it can be difficult to reproduce results in situations where that is useful such as testing or saving game states or similar   In those situations  the pre-Java 1 7 technique shown below can be used   Before Java 1 7  the standard way to do this is as follows   import java util Random          Returns a pseudo-random number between min and max  inclusive     The difference between min and max can be at most     lt code gt Integer MAX VALUE - 1 lt  code gt          param min Minimum value     param max Maximum value   Must be greater than min      return Integer between min and max  inclusive      see java util Random nextInt int      public static int randInt int min  int max            NOTE  This will  intentionally  not run as written so that folks        copy-pasting have to think about how to initialize their        Random instance   Initialization of the Random instance is outside        the main scope of the question  but some decent options are to have        a field that is initialized once and then re-used as needed or to        use ThreadLocalRandom  if using at least Java 1 7                  In particular  do NOT do  Random rand   new Random    here or you        will get not very good   not very random results      Random rand          nextInt is normally exclusive of the top value         so add 1 to make it inclusive     int randomNum   rand nextInt  max - min    1    min       return randomNum      See the relevant JavaDoc   In practice  the java util Random class is often preferable to java lang Math random     In particular  there is no need to reinvent the random integer generation wheel when there is a straightforward API within the standard library to accomplish the task

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Using Java 8 Streams    Pass the initialCapacity - How many numbers Pass the randomBound - from x to randomBound Pass true false for sorted or not Pass an new Random   object    nbsp   public static List lt Integer gt  generateNumbers int initialCapacity  int randomBound  Boolean sorted  Random random         List lt Integer gt  numbers   random ints initialCapacity  1  randomBound  boxed   collect Collectors toList          if  sorted          numbers sort null        return numbers      It generates numbers from 1-Randombound in this example

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You can achieve that concisely in Java 8   Random random   new Random     int max   10  int min   5  int totalNumber   10   IntStream stream   random ints totalNumber  min  max   stream forEach System out  println

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Use java util for Random for general use   You can define your minimum and maximum range to get those results   Random rand new Random    rand nextInt  max 1  - min    min

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int random   minimum   Double valueOf Math random    maximum-minimum    intValue      Or take a look to RandomUtils from Apache Commons

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Here is a simple sample that shows how to generate random number from closed  min  max  range  while min  lt   max is true  You can reuse it as field in hole class  also having all Random class methods in one place  Results example   RandomUtils random   new RandomUtils    random nextInt 0  0      returns 0 random nextInt 10  10      returns 10 random nextInt -10  10      returns numbers from -10 to 10  -10  -9    9  10  random nextInt 10  -10      throws assert   Sources   import junit framework Assert  import java util Random   public class RandomUtils extends Random                    param min generated value  Can t be  gt  then max         param max generated value         return values in closed range  min  max               public int nextInt int min  int max            Assert assertFalse  min can t be  gt  then max  values      min          max        min  gt  max           if  min    max                return max                     return nextInt max - min   1    min

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Just a small modification of your first solution would suffice   Random rand   new Random    randomNum   minimum   rand nextInt  maximum - minimum    1       See more here for implementation of Random

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Using Java 8 Streams    Pass the initialCapacity - How many numbers Pass the randomBound - from x to randomBound Pass true false for sorted or not Pass an new Random   object    nbsp   public static List lt Integer gt  generateNumbers int initialCapacity  int randomBound  Boolean sorted  Random random         List lt Integer gt  numbers   random ints initialCapacity  1  randomBound  boxed   collect Collectors toList          if  sorted          numbers sort null        return numbers      It generates numbers from 1-Randombound in this example

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The Math Random class in Java is 0-based  So  if you write something like this    Random rand   new Random    int x   rand nextInt 10     x will be between 0-9 inclusive   So  given the following array of 25 items  the code to generate a random number between 0  the base of the array  and array length would be   String   i   new String 25   Random rand   new Random    int index   0   index   rand nextInt  i length      Since i length will return 25  the nextInt  i length   will return a number between the range of 0-24  The other option is going with Math Random which works in the same way   index    int  Math floor Math random     i length     For a better understanding  check out forum post Random Intervals  archive org

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Here s a helpful class to generate random ints in a range with any combination of inclusive exclusive bounds   import java util Random   public class RandomRange extends Random       public int nextIncInc int min  int max            return nextInt max - min   1    min             public int nextExcInc int min  int max            return nextInt max - min    1   min             public int nextExcExc int min  int max            return nextInt max - min - 1    1   min             public int nextIncExc int min  int max            return nextInt max - min    min

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To avoid repeating what have been said multiple times  I am showing an alternative for those that need a cryptographically stronger pseudo-random number generator by using the SecureRandom class  which extends the class Random   From source one can read   This class provides a cryptographically strong random number generator  RNG   A cryptographically strong random number minimally complies with the statistical random number generator tests specified in FIPS 140-2  Security Requirements for Cryptographic Modules  section 4 9 1  Additionally  SecureRandom must produce non-deterministic output  Therefore any seed material passed to a SecureRandom object must be unpredictable  and all SecureRandom output sequences must be cryptographically strong  as described in RFC 1750  Randomness Recommendations for Security  A caller obtains a SecureRandom instance via the no-argument constructor or one of the getInstance methods    SecureRandom random   new SecureRandom       Many SecureRandom implementations are in the form of a pseudo-random number generator  PRNG   which means they use a deterministic algorithm to produce a pseudo-random sequence from a true random seed  Other implementations may produce true random numbers  and yet others may use a combination of both techniques   To generate a random number between a min and max values inclusive  public static int generate SecureRandom secureRandom  int min  int max            return min   secureRandom nextInt  max - min    1      for a given a min  inclusive  and max  exclusive  values  return min   secureRandom nextInt  max - min     A running code example  public class Main        public static int generate SecureRandom secureRandom  int min  int max            return min   secureRandom nextInt  max - min    1              public static void main String   arg            SecureRandom random   new SecureRandom            System out println generate random  0  2              Source such as stackoverflow  baeldung  geeksforgeeks provide comparisons between Random and SecureRandom classes  From baeldung one can read   The most common way of using SecureRandom is to generate int  long  float  double or boolean values  int randomInt   secureRandom nextInt     long randomLong   secureRandom nextLong      float randomFloat   secureRandom nextFloat      double randomDouble   secureRandom nextDouble      boolean randomBoolean   secureRandom nextBoolean      For generating int values we can pass an upper bound as a parameter  int randomInt   secureRandom nextInt upperBound    In addition  we can generate a stream of values for int  double and long  IntStream randomIntStream   secureRandom ints     LongStream randomLongStream   secureRandom longs     DoubleStream randomDoubleStream   secureRandom doubles     For all streams we can explicitly set the stream size  IntStream intStream   secureRandom ints streamSize    This class offers several other options  e g   choosing the underlying random number generator  that are out of the scope of this question

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I have created a method to get a unique integer in a given range              minNum is the minimum possible random number         maxNum is the maximum possible random number         numbersNeeded is the quantity of random number required         the give method provides you with unique random number between min  amp  max range    public static Set lt Integer gt  getUniqueRandomNumbers  int minNum   int maxNum  int numbersNeeded         if minNum  gt   maxNum          throw new IllegalArgumentException  maxNum must be greater than minNum         if    numbersNeeded  gt   maxNum - minNum   1             throw new IllegalArgumentException  numberNeeded must be greater then difference b w  max- min  1          Random rng   new Random       Ideally just create one instance globally         Note  use LinkedHashSet to maintain insertion order     Set lt Integer gt  generated   new LinkedHashSet lt Integer gt         while  generated size    lt  numbersNeeded                Integer next   rng nextInt  maxNum - minNum    1    minNum              As we re adding to a set  this will automatically do a containment check         generated add next             return generated

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Another option is just using Apache Commons    import org apache commons math random RandomData  import org apache commons math random RandomDataImpl   public void method         RandomData randomData   new RandomDataImpl        int number   randomData nextInt 5  10

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Say you want range between 0-9  0 is minimum and 9 is maximum  The below function will print anything between 0 and 9  It s the same for all ranges   public static void main String   args        int b   randomNumberRange 0  9       int d   randomNumberRange  100  200       System out println  value of b is     b       System out println  value of d is     d      public static int randomNumberRange int min  int max        int n    max   1 - min    min      return  int   Math random     n

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Note that this approach is more biased and less efficient than a nextInt approach  https   stackoverflow com a 738651 360211  One standard pattern for accomplishing this is   Min    int  Math random       Max - Min    1     The Java Math library function Math random   generates a double value in the range  0 1   Notice this range does not include the 1   In order to get a specific range of values first  you need to multiply by the magnitude of the range of values you want covered    Math random       Max - Min     This returns a value in the range  0 Max-Min   where  Max-Min  is not included   For example  if you want  5 10   you need to cover five integer values so you use  Math random     5   This would return a value in the range  0 5   where 5 is not included   Now you need to shift this range up to the range that you are targeting  You do this by adding the Min value   Min    Math random      Max - Min     You now will get a value in the range  Min Max   Following our example  that means  5 10    5    Math random      10 - 5     But  this still doesn t include Max and you are getting a double value  In order to get the Max value included  you need to add 1 to your range parameter  Max - Min  and then truncate the decimal part by casting to an int  This is accomplished via   Min    int  Math random       Max - Min    1     And there you have it  A random integer value in the range  Min Max   or per the example  5 10    5    int  Math random       10 - 5    1

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If you already use Commons Lang API 2 x or latest version then there is one class for random number generation RandomUtils   public static int nextInt int n    Returns a pseudorandom  uniformly distributed int value between 0  inclusive  and the specified value  exclusive   from the Math random   sequence   Parameters  n - the specified exclusive max-value  int random   RandomUtils nextInt 1000000     Note  In RandomUtils have many methods for random number generation

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Generate a random number for the difference of min and max by using the nextint n  method and then add min number to the result   Random rn   new Random    int result   rn nextInt max - min   1    min  System out println result

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There is a library at https   sourceforge net projects stochunit  for handling selection of ranges   StochIntegerSelector randomIntegerSelector   new StochIntegerSelector    randomIntegerSelector setMin -1   randomIntegerSelector setMax 1   Integer selectInteger   randomIntegerSelector selectInteger      It has edge inclusion preclusion

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I use this              param min - The minimum        param max - The maximum        return A random double between these numbers  inclusive the minimum and maximum          public static double getRandom double min  double max       return  Math random      max   1 - min     min       You can cast it to an Integer if you want

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I think this code will work for it  Please try this    import java util Random  public final class RandomNumber        public static final void main String    aArgs            log  Generating 10 random integers in range 1  10             int START   1          int END   10          Random randomGenerator   new Random            for  int idx 1  idx lt  10    idx                    int randomInt randomGenerator nextInt 100                  log  Generated       randomInt               showRandomInteger START END randomGenerator                     log  Done               private static void log String aMessage            System out println aMessage              private static void showRandomInteger int aStart  int aEnd  Random aRandom            if  aStart  gt  aEnd                throw new IllegalArgumentException  Start cannot exceed End                       long range    long aEnd -  long aStart   1          long fraction    long   range   aRandom nextDouble             int randomNumber    int   fraction   aStart           log  Generated    randomNumber

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I think this code will work for it  Please try this    import java util Random  public final class RandomNumber        public static final void main String    aArgs            log  Generating 10 random integers in range 1  10             int START   1          int END   10          Random randomGenerator   new Random            for  int idx 1  idx lt  10    idx                    int randomInt randomGenerator nextInt 100                  log  Generated       randomInt               showRandomInteger START END randomGenerator                     log  Done               private static void log String aMessage            System out println aMessage              private static void showRandomInteger int aStart  int aEnd  Random aRandom            if  aStart  gt  aEnd                throw new IllegalArgumentException  Start cannot exceed End                       long range    long aEnd -  long aStart   1          long fraction    long   range   aRandom nextDouble             int randomNumber    int   fraction   aStart           log  Generated    randomNumber

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The Math Random class in Java is 0-based  So  if you write something like this    Random rand   new Random    int x   rand nextInt 10     x will be between 0-9 inclusive   So  given the following array of 25 items  the code to generate a random number between 0  the base of the array  and array length would be   String   i   new String 25   Random rand   new Random    int index   0   index   rand nextInt  i length      Since i length will return 25  the nextInt  i length   will return a number between the range of 0-24  The other option is going with Math Random which works in the same way   index    int  Math floor Math random     i length     For a better understanding  check out forum post Random Intervals  archive org

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int random   minimum   Double valueOf Math random    maximum-minimum    intValue      Or take a look to RandomUtils from Apache Commons

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You could use   RandomStringUtils randomNumeric int count    method also which is from apache commons

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You can use this code snippet which will resolve your problem    Random r   new Random    int myRandomNumber   0  myRandomNumber   r nextInt maxValue-minValue 1  minValue    Use myRandomNumber  which will give you a number within a range

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Note that this approach is more biased and less efficient than a nextInt approach  https   stackoverflow com a 738651 360211  One standard pattern for accomplishing this is   Min    int  Math random       Max - Min    1     The Java Math library function Math random   generates a double value in the range  0 1   Notice this range does not include the 1   In order to get a specific range of values first  you need to multiply by the magnitude of the range of values you want covered    Math random       Max - Min     This returns a value in the range  0 Max-Min   where  Max-Min  is not included   For example  if you want  5 10   you need to cover five integer values so you use  Math random     5   This would return a value in the range  0 5   where 5 is not included   Now you need to shift this range up to the range that you are targeting  You do this by adding the Min value   Min    Math random      Max - Min     You now will get a value in the range  Min Max   Following our example  that means  5 10    5    Math random      10 - 5     But  this still doesn t include Max and you are getting a double value  In order to get the Max value included  you need to add 1 to your range parameter  Max - Min  and then truncate the decimal part by casting to an int  This is accomplished via   Min    int  Math random       Max - Min    1     And there you have it  A random integer value in the range  Min Max   or per the example  5 10    5    int  Math random       10 - 5    1

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Random number from the range  min  max  inclusive   int randomFromMinToMaxInclusive   ThreadLocalRandom current            nextInt min  max   1

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Here is a simple sample that shows how to generate random number from closed  min  max  range  while min  lt   max is true  You can reuse it as field in hole class  also having all Random class methods in one place  Results example   RandomUtils random   new RandomUtils    random nextInt 0  0      returns 0 random nextInt 10  10      returns 10 random nextInt -10  10      returns numbers from -10 to 10  -10  -9    9  10  random nextInt 10  -10      throws assert   Sources   import junit framework Assert  import java util Random   public class RandomUtils extends Random                    param min generated value  Can t be  gt  then max         param max generated value         return values in closed range  min  max               public int nextInt int min  int max            Assert assertFalse  min can t be  gt  then max  values      min          max        min  gt  max           if  min    max                return max                     return nextInt max - min   1    min

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You could use   RandomStringUtils randomNumeric int count    method also which is from apache commons

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The Math Random class in Java is 0-based  So  if you write something like this    Random rand   new Random    int x   rand nextInt 10     x will be between 0-9 inclusive   So  given the following array of 25 items  the code to generate a random number between 0  the base of the array  and array length would be   String   i   new String 25   Random rand   new Random    int index   0   index   rand nextInt  i length      Since i length will return 25  the nextInt  i length   will return a number between the range of 0-24  The other option is going with Math Random which works in the same way   index    int  Math floor Math random     i length     For a better understanding  check out forum post Random Intervals  archive org

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It s better to use SecureRandom rather than just Random   public static int generateRandomInteger int min  int max        SecureRandom rand   new SecureRandom        rand setSeed new Date   getTime         int randomNum   rand nextInt  max - min    1    min      return randomNum

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In case of rolling a dice it would be random number between 1 to 6  not 0 to 6   so    face   1   randomNumbers nextInt 6

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You can use this code snippet which will resolve your problem    Random r   new Random    int myRandomNumber   0  myRandomNumber   r nextInt maxValue-minValue 1  minValue    Use myRandomNumber  which will give you a number within a range

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private static Random random   new Random         public static int getRandomInt int min  int max     return random nextInt max - min   1    min      OR  public static int getRandomInt Random random  int min  int max      return random nextInt max - min   1    min

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You can do something like this   import java awt    import java io    import java util    import java math     public class Test        public static void main String   args            int first  second           Scanner myScanner   new Scanner System in            System out println  Enter first integer              int numOne          numOne   myScanner nextInt            System out println  You have keyed in     numOne            System out println  Enter second integer              int numTwo          numTwo   myScanner nextInt            System out println  You have keyed in     numTwo            Random generator   new Random            int num    int  Math random   numTwo           System out println  Random number        num gt numOne  num numOne num

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here s a function that returns exactly one integer random number in a range defined by lowerBoundIncluded and upperBoundIncluded  as requested by user42155  SplittableRandom splittableRandom   new SplittableRandom     BiFunction lt Integer Integer Integer gt  randomInt    lowerBoundIncluded  upperBoundIncluded      - gt  splittableRandom nextInt  lowerBoundIncluded  upperBoundIncluded   1      randomInt apply                  gets the random number     or shorter for the one-time generation of a random number  new SplittableRandom   nextInt  lowerBoundIncluded  upperBoundIncluded   1

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A simple way to generate n random numbers between a and b e g a  90  b 100  n  20  Random r   new Random    for int i  0  i lt 20  i         System out println r ints 90  100  iterator   nextInt         r ints   returns an IntStream and has several useful methods  have look at its API

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A simple way to generate n random numbers between a and b e g a  90  b 100  n  20  Random r   new Random    for int i  0  i lt 20  i         System out println r ints 90  100  iterator   nextInt         r ints   returns an IntStream and has several useful methods  have look at its API

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public static Random RANDOM   new Random System nanoTime      public static final float random final float pMin  final float pMax        return pMin   RANDOM nextFloat      pMax - pMin

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I will simply state what is wrong with the solutions provided by the question and why the errors    Solution 1   randomNum   minimum    int  Math random   maximum      Problem  randomNum is assigned values numbers bigger than maximum   Explanation  Suppose our minimum is 5  and your maximum is 10  Any value from Math random   greater than 0 6 will make the expression evaluate to 6 or greater  and adding 5 makes it greater than 10  your maximum   The problem is you are multiplying the random number by the maximum  which generates a number almost as big as the maximum  and then adding the minimum  Unless the minimum is 1  it s not correct  You have to switch to  as mentioned in other answers  randomNum   minimum    int  Math random    maximum-minimum 1     The  1 is because Math random   will never return 1 0   Solution 2   Random rn   new Random    int n   maximum - minimum   1  int i   rn nextInt     n  randomNum    minimum   i    Your problem here is that     may return a negative number if the first term is smaller than 0  Since rn nextInt   returns negative values with  50  chance  you will also not get the expected result   This  was  however  almost perfect  You just had to look a bit further down the Javadoc  nextInt int n   With that method available  doing  Random rn   new Random    int n   maximum - minimum   1  int i   rn nextInt n   randomNum    minimum   i    Would also return the desired result

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I just generate a random number using Math random   and multiply it by a big number  let s say 10000   So  I get a number between 0 to 10 000 and call this number i  Now  if I need numbers between  x  y   then do the following   i   x    i    y - x      So  all i s are numbers between x and y   To remove the bias as pointed out in the comments  rather than multiplying it by 10000  or the big number   multiply it by  y-x

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I am thinking to linearly normalize the generated random numbers into desired range by using the following  Let x be a random number  let a and b be the minimum and maximum range of desired normalized number   Then below is just a very simple code snipplet to test the range produced by the linear mapping   public static void main String   args        int a   100      int b   1000      int lowest   b      int highest   a      int count   100000      Random random   new Random        for  int i   0  i  lt  count  i              int nextNumber    int    Math abs random nextDouble       b - a      a          if  nextNumber  lt  a    nextNumber  gt  b                System err println  number not in range      nextNumber                     else               System out println nextNumber                     if  nextNumber  lt  lowest                lowest   nextNumber                    if  nextNumber  gt  highest                highest   nextNumber                      System out println  Produced     count     numbers from     lowest                 to     highest

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I wonder if any of the random number generating methods provided by an Apache Commons Math library would fit the bill    For example  RandomDataGenerator nextInt or RandomDataGenerator nextLong

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Random random   new Random    int max   10  int min   3  int randomNum   random nextInt max     max - min   1    min

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One of my friends had asked me this same question in university today  his requirements was to generate a random number between 1  amp  -1   So I wrote this  and it works fine so far with my testing  There are ideally a lot of ways to generate random numbers given a range  Try this    Function   private static float getRandomNumberBetween float numberOne  float numberTwo  throws Exception       if  numberOne    numberTwo           throw new Exception  Both the numbers can not be equal               float rand    float  Math random        float highRange   Math max numberOne  numberTwo       float lowRange   Math min numberOne  numberTwo        float lowRand    float  Math floor rand-1       float highRand    float  Math ceil rand 1        float genRand    highRange-lowRange    rand-lowRand   highRand-lowRand   lowRange       return genRand      Execute like this   System out println  getRandomNumberBetween 1 -1

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import java util Random    public class RandomUtil          Declare as class variable so that it is not re-seeded every call     private static Random random   new Random                    Returns a psuedo-random number between min and max  both inclusive          param min Minimim value         param max Maximim value  Must be greater than min          return Integer between min and max  both inclusive          see java util Random nextInt int              public static int nextInt int min  int max               nextInt is normally exclusive of the top value             so add 1 to make it inclusive         return random nextInt  max - min    1    min

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One of my friends had asked me this same question in university today  his requirements was to generate a random number between 1  amp  -1   So I wrote this  and it works fine so far with my testing  There are ideally a lot of ways to generate random numbers given a range  Try this    Function   private static float getRandomNumberBetween float numberOne  float numberTwo  throws Exception       if  numberOne    numberTwo           throw new Exception  Both the numbers can not be equal               float rand    float  Math random        float highRange   Math max numberOne  numberTwo       float lowRange   Math min numberOne  numberTwo        float lowRand    float  Math floor rand-1       float highRand    float  Math ceil rand 1        float genRand    highRange-lowRange    rand-lowRand   highRand-lowRand   lowRange       return genRand      Execute like this   System out println  getRandomNumberBetween 1 -1

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int random   minimum   Double valueOf Math random    maximum-minimum    intValue      Or take a look to RandomUtils from Apache Commons

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Most of above suggestion don t consider  overflow   For example  min   Integer MIN VALUE  max   100  One of correct approaches I have so far is   final long mod   max- min   1L  final int next    int   Math abs rand nextLong     mod    min

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Most of above suggestion don t consider  overflow   For example  min   Integer MIN VALUE  max   100  One of correct approaches I have so far is   final long mod   max- min   1L  final int next    int   Math abs rand nextLong     mod    min

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Just a small modification of your first solution would suffice   Random rand   new Random    randomNum   minimum   rand nextInt  maximum - minimum    1       See more here for implementation of Random

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The below code generates a random number between 100 000 and 900 000  This code will generate six digit values  I m using this code to generate a six-digit OTP   Use import java util Random to use this random method   import java util Random      Six digits random number generation for OTP Random rnd   new Random    long longregisterOTP   100000   rnd nextInt 900000   System out println longregisterOTP

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Use Apache Lang3 Commons Integer parseInt RandomStringUtils randomNumeric 6  6     Min Value 100000 to Max Value 999999

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public static Random RANDOM   new Random System nanoTime      public static final float random final float pMin  final float pMax        return pMin   RANDOM nextFloat      pMax - pMin

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This will generate Random numbers list with range  Min - Max  with no duplicate   generateRandomListNoDuplicate 1000  8000  500     Add this method   private void generateRandomListNoDuplicate int min  int max  int totalNoRequired        Random rng   new Random        Set lt Integer gt  generatedList   new LinkedHashSet lt  gt         while  generatedList size    lt  totalNoRequired            Integer radnomInt   rng nextInt max - min   1    min          generatedList add radnomInt             Hope this will help you

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The below code generates a random number between 100 000 and 900 000  This code will generate six digit values  I m using this code to generate a six-digit OTP   Use import java util Random to use this random method   import java util Random      Six digits random number generation for OTP Random rnd   new Random    long longregisterOTP   100000   rnd nextInt 900000   System out println longregisterOTP

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In case of rolling a dice it would be random number between 1 to 6  not 0 to 6   so    face   1   randomNumbers nextInt 6

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Just use the Random class    Random ran   new Random       Assumes max and min are non-negative  int randomInt   min   ran nextInt max - min   1

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int random   minimum   Double valueOf Math random    maximum-minimum    intValue      Or take a look to RandomUtils from Apache Commons

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here s a function that returns exactly one integer random number in a range defined by lowerBoundIncluded and upperBoundIncluded  as requested by user42155  SplittableRandom splittableRandom   new SplittableRandom     BiFunction lt Integer Integer Integer gt  randomInt    lowerBoundIncluded  upperBoundIncluded      - gt  splittableRandom nextInt  lowerBoundIncluded  upperBoundIncluded   1      randomInt apply                  gets the random number     or shorter for the one-time generation of a random number  new SplittableRandom   nextInt  lowerBoundIncluded  upperBoundIncluded   1

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Just use the Random class    Random ran   new Random       Assumes max and min are non-negative  int randomInt   min   ran nextInt max - min   1

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Making the following change in Attempt 1 should do the work -   randomNum   minimum    int  Math random      maximum - minimum       Check this for working code

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Try using org apache commons lang RandomStringUtils class  Yes  it sometimes give a  repeated number adjacently  but it will give the value between 5 and 15       while  true                int abc   Integer valueOf RandomStringUtils randomNumeric 1            int cd   Integer valueOf RandomStringUtils randomNumeric 2            if   cd-abc   gt   5  amp  amp   cd-abc   lt   15                        System out println cd-abc               break

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Use   minimum   rn nextInt maxValue - minvalue   1

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Use   Random ran   new Random    int x   ran nextInt 6    5    The integer x is now the random number that has a possible outcome of 5-10

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I have created a method to get a unique integer in a given range              minNum is the minimum possible random number         maxNum is the maximum possible random number         numbersNeeded is the quantity of random number required         the give method provides you with unique random number between min  amp  max range    public static Set lt Integer gt  getUniqueRandomNumbers  int minNum   int maxNum  int numbersNeeded         if minNum  gt   maxNum          throw new IllegalArgumentException  maxNum must be greater than minNum         if    numbersNeeded  gt   maxNum - minNum   1             throw new IllegalArgumentException  numberNeeded must be greater then difference b w  max- min  1          Random rng   new Random       Ideally just create one instance globally         Note  use LinkedHashSet to maintain insertion order     Set lt Integer gt  generated   new LinkedHashSet lt Integer gt         while  generated size    lt  numbersNeeded                Integer next   rng nextInt  maxNum - minNum    1    minNum              As we re adding to a set  this will automatically do a containment check         generated add next             return generated

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I wonder if any of the random number generating methods provided by an Apache Commons Math library would fit the bill    For example  RandomDataGenerator nextInt or RandomDataGenerator nextLong

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rand nextInt  max 1  - min    min    This is working fine

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It can be done by simply doing the statement   Randomizer generate 0 10     min of zero  max of ten   Below is its source-code  Randomizer java  public class Randomizer       public static int generate int min int max            return min    int  Math random       max - min    1              It is just clean and simple

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You can do something like this   import java awt    import java io    import java util    import java math     public class Test        public static void main String   args            int first  second           Scanner myScanner   new Scanner System in            System out println  Enter first integer              int numOne          numOne   myScanner nextInt            System out println  You have keyed in     numOne            System out println  Enter second integer              int numTwo          numTwo   myScanner nextInt            System out println  You have keyed in     numTwo            Random generator   new Random            int num    int  Math random   numTwo           System out println  Random number        num gt numOne  num numOne num

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In Java 1 7 or later  the standard way to do this is as follows   import java util concurrent ThreadLocalRandom      nextInt is normally exclusive of the top value     so add 1 to make it inclusive int randomNum   ThreadLocalRandom current   nextInt min  max   1     See the relevant JavaDoc   This approach has the advantage of not needing to explicitly initialize a java util Random instance  which can be a source of confusion and error if used inappropriately   However  conversely there is no way to explicitly set the seed so it can be difficult to reproduce results in situations where that is useful such as testing or saving game states or similar   In those situations  the pre-Java 1 7 technique shown below can be used   Before Java 1 7  the standard way to do this is as follows   import java util Random          Returns a pseudo-random number between min and max  inclusive     The difference between min and max can be at most     lt code gt Integer MAX VALUE - 1 lt  code gt          param min Minimum value     param max Maximum value   Must be greater than min      return Integer between min and max  inclusive      see java util Random nextInt int      public static int randInt int min  int max            NOTE  This will  intentionally  not run as written so that folks        copy-pasting have to think about how to initialize their        Random instance   Initialization of the Random instance is outside        the main scope of the question  but some decent options are to have        a field that is initialized once and then re-used as needed or to        use ThreadLocalRandom  if using at least Java 1 7                  In particular  do NOT do  Random rand   new Random    here or you        will get not very good   not very random results      Random rand          nextInt is normally exclusive of the top value         so add 1 to make it inclusive     int randomNum   rand nextInt  max - min    1    min       return randomNum      See the relevant JavaDoc   In practice  the java util Random class is often preferable to java lang Math random     In particular  there is no need to reinvent the random integer generation wheel when there is a straightforward API within the standard library to accomplish the task

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Use Apache Lang3 Commons Integer parseInt RandomStringUtils randomNumeric 6  6     Min Value 100000 to Max Value 999999

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Note that this approach is more biased and less efficient than a nextInt approach  https   stackoverflow com a 738651 360211  One standard pattern for accomplishing this is   Min    int  Math random       Max - Min    1     The Java Math library function Math random   generates a double value in the range  0 1   Notice this range does not include the 1   In order to get a specific range of values first  you need to multiply by the magnitude of the range of values you want covered    Math random       Max - Min     This returns a value in the range  0 Max-Min   where  Max-Min  is not included   For example  if you want  5 10   you need to cover five integer values so you use  Math random     5   This would return a value in the range  0 5   where 5 is not included   Now you need to shift this range up to the range that you are targeting  You do this by adding the Min value   Min    Math random      Max - Min     You now will get a value in the range  Min Max   Following our example  that means  5 10    5    Math random      10 - 5     But  this still doesn t include Max and you are getting a double value  In order to get the Max value included  you need to add 1 to your range parameter  Max - Min  and then truncate the decimal part by casting to an int  This is accomplished via   Min    int  Math random       Max - Min    1     And there you have it  A random integer value in the range  Min Max   or per the example  5 10    5    int  Math random       10 - 5    1

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You can edit your second code example to   Random rn   new Random    int range   maximum - minimum   1  int randomNum    rn nextInt range    minimum

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To avoid repeating what have been said multiple times  I am showing an alternative for those that need a cryptographically stronger pseudo-random number generator by using the SecureRandom class  which extends the class Random   From source one can read   This class provides a cryptographically strong random number generator  RNG   A cryptographically strong random number minimally complies with the statistical random number generator tests specified in FIPS 140-2  Security Requirements for Cryptographic Modules  section 4 9 1  Additionally  SecureRandom must produce non-deterministic output  Therefore any seed material passed to a SecureRandom object must be unpredictable  and all SecureRandom output sequences must be cryptographically strong  as described in RFC 1750  Randomness Recommendations for Security  A caller obtains a SecureRandom instance via the no-argument constructor or one of the getInstance methods    SecureRandom random   new SecureRandom       Many SecureRandom implementations are in the form of a pseudo-random number generator  PRNG   which means they use a deterministic algorithm to produce a pseudo-random sequence from a true random seed  Other implementations may produce true random numbers  and yet others may use a combination of both techniques   To generate a random number between a min and max values inclusive  public static int generate SecureRandom secureRandom  int min  int max            return min   secureRandom nextInt  max - min    1      for a given a min  inclusive  and max  exclusive  values  return min   secureRandom nextInt  max - min     A running code example  public class Main        public static int generate SecureRandom secureRandom  int min  int max            return min   secureRandom nextInt  max - min    1              public static void main String   arg            SecureRandom random   new SecureRandom            System out println generate random  0  2              Source such as stackoverflow  baeldung  geeksforgeeks provide comparisons between Random and SecureRandom classes  From baeldung one can read   The most common way of using SecureRandom is to generate int  long  float  double or boolean values  int randomInt   secureRandom nextInt     long randomLong   secureRandom nextLong      float randomFloat   secureRandom nextFloat      double randomDouble   secureRandom nextDouble      boolean randomBoolean   secureRandom nextBoolean      For generating int values we can pass an upper bound as a parameter  int randomInt   secureRandom nextInt upperBound    In addition  we can generate a stream of values for int  double and long  IntStream randomIntStream   secureRandom ints     LongStream randomLongStream   secureRandom longs     DoubleStream randomDoubleStream   secureRandom doubles     For all streams we can explicitly set the stream size  IntStream intStream   secureRandom ints streamSize    This class offers several other options  e g   choosing the underlying random number generator  that are out of the scope of this question

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If you already use Commons Lang API 2 x or latest version then there is one class for random number generation RandomUtils   public static int nextInt int n    Returns a pseudorandom  uniformly distributed int value between 0  inclusive  and the specified value  exclusive   from the Math random   sequence   Parameters  n - the specified exclusive max-value  int random   RandomUtils nextInt 1000000     Note  In RandomUtils have many methods for random number generation

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The Math Random class in Java is 0-based  So  if you write something like this    Random rand   new Random    int x   rand nextInt 10     x will be between 0-9 inclusive   So  given the following array of 25 items  the code to generate a random number between 0  the base of the array  and array length would be   String   i   new String 25   Random rand   new Random    int index   0   index   rand nextInt  i length      Since i length will return 25  the nextInt  i length   will return a number between the range of 0-24  The other option is going with Math Random which works in the same way   index    int  Math floor Math random     i length     For a better understanding  check out forum post Random Intervals  archive org

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A different approach using Java 8 IntStream and Collections shuffle  import java util stream IntStream  import java util ArrayList  import java util Collections   public class Main        public static void main String   args             IntStream range   IntStream rangeClosed 5 10           ArrayList lt Integer gt  ls    new ArrayList lt Integer gt                populate the ArrayList         range forEach i - gt  ls add new Integer i                 perform a random shuffle  using the Collections Fisher-Yates shuffle         Collections shuffle ls           System out println ls             The equivalent in Scala  import scala util Random  object RandomRange extends App    val x    Random shuffle 5 to 10      println x

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In Java 1 7 or later  the standard way to do this is as follows   import java util concurrent ThreadLocalRandom      nextInt is normally exclusive of the top value     so add 1 to make it inclusive int randomNum   ThreadLocalRandom current   nextInt min  max   1     See the relevant JavaDoc   This approach has the advantage of not needing to explicitly initialize a java util Random instance  which can be a source of confusion and error if used inappropriately   However  conversely there is no way to explicitly set the seed so it can be difficult to reproduce results in situations where that is useful such as testing or saving game states or similar   In those situations  the pre-Java 1 7 technique shown below can be used   Before Java 1 7  the standard way to do this is as follows   import java util Random          Returns a pseudo-random number between min and max  inclusive     The difference between min and max can be at most     lt code gt Integer MAX VALUE - 1 lt  code gt          param min Minimum value     param max Maximum value   Must be greater than min      return Integer between min and max  inclusive      see java util Random nextInt int      public static int randInt int min  int max            NOTE  This will  intentionally  not run as written so that folks        copy-pasting have to think about how to initialize their        Random instance   Initialization of the Random instance is outside        the main scope of the question  but some decent options are to have        a field that is initialized once and then re-used as needed or to        use ThreadLocalRandom  if using at least Java 1 7                  In particular  do NOT do  Random rand   new Random    here or you        will get not very good   not very random results      Random rand          nextInt is normally exclusive of the top value         so add 1 to make it inclusive     int randomNum   rand nextInt  max - min    1    min       return randomNum      See the relevant JavaDoc   In practice  the java util Random class is often preferable to java lang Math random     In particular  there is no need to reinvent the random integer generation wheel when there is a straightforward API within the standard library to accomplish the task

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int func int max  int min          int range   max - min   1                  Math random   function will return a random no between  0 0 1 0         int res    int    Math random   range  min         return res

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Random random   new Random    int max   10  int min   3  int randomNum   random nextInt max     max - min   1    min

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You can use following way to do that int range   10  int min   5 Random r   new Random    int    r nextInt range    min

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Forgive me for being fastidious  but the solution suggested by the majority  i e   min   rng nextInt max - min   1    seems perilous due to the fact that    rng nextInt n  cannot reach Integer MAX VALUE   max - min  may cause overflow when min is negative    A foolproof solution would return correct results for any min  lt   max within  Integer MIN VALUE  Integer MAX VALUE   Consider the following naive implementation   int nextIntInRange int min  int max  Random rng       if  min  gt  max          throw new IllegalArgumentException  Cannot draw random int from invalid range      min          max                  int diff   max - min     if  diff  gt   0  amp  amp  diff    Integer MAX VALUE          return  min   rng nextInt diff   1            int i     do         i   rng nextInt         while  i  lt  min    i  gt  max      return i      Although inefficient  note that the probability of success in the while loop will always be 50  or higher

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Use   minimum   rn nextInt maxValue - minvalue   1

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This methods might be convenient to use   This method will return a random number between the provided min and max value   public static int getRandomNumberBetween int min  int max        Random foo   new Random        int randomNumber   foo nextInt max - min    min      if  randomNumber    min               Since the random number is between the min and max values  simply add 1         return min   1        else           return randomNumber            and this method will return a random number from the provided min and max value  so the generated number could also be the min or max number    public static int getRandomNumberFrom int min  int max        Random foo   new Random        int randomNumber   foo nextInt  max   1  - min    min       return randomNumber

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import java util Random   public class RandomSSNTest        public static void main String args              generateDummySSNNumber                  831-33-6049     public static void generateDummySSNNumber             Random random   new Random             int id1   random nextInt 1000    3         int id2   random nextInt 100    2         int id3   random nextInt 10000    4          System out print  id1  -  id2  -  id3               You can also use   import java util concurrent ThreadLocalRandom  Random random   ThreadLocalRandom current      However  this class doesn   t perform well in a multi-threaded environment

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This is the easy way to do this   import java util Random  class Example      public static void main String args               -To test-         for int i   1  i lt 20   i                 System out print randomnumber                                       int randomnumber   randomnumber                public static int randomnumber            Random rand   new Random            int randomNum   rand nextInt 6    5           return randomNum            In there 5 is the starting point of random numbers  6 is the range including number 5

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Try using org apache commons lang RandomStringUtils class  Yes  it sometimes give a  repeated number adjacently  but it will give the value between 5 and 15       while  true                int abc   Integer valueOf RandomStringUtils randomNumeric 1            int cd   Integer valueOf RandomStringUtils randomNumeric 2            if   cd-abc   gt   5  amp  amp   cd-abc   lt   15                        System out println cd-abc               break

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A different approach using Java 8 IntStream and Collections shuffle  import java util stream IntStream  import java util ArrayList  import java util Collections   public class Main        public static void main String   args             IntStream range   IntStream rangeClosed 5 10           ArrayList lt Integer gt  ls    new ArrayList lt Integer gt                populate the ArrayList         range forEach i - gt  ls add new Integer i                 perform a random shuffle  using the Collections Fisher-Yates shuffle         Collections shuffle ls           System out println ls             The equivalent in Scala  import scala util Random  object RandomRange extends App    val x    Random shuffle 5 to 10      println x

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You can edit your second code example to   Random rn   new Random    int range   maximum - minimum   1  int randomNum    rn nextInt range    minimum

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rand nextInt  max 1  - min    min

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I found this example Generate random numbers       This example generates random integers in a specific range    import java util Random       Generate random integers in a certain range     public final class RandomRange      public static final void main String    aArgs       log  Generating random integers in the range 1  10          int START   1      int END   10      Random random   new Random        for  int idx   1  idx  lt   10    idx         showRandomInteger START  END  random              log  Done            private static void showRandomInteger int aStart  int aEnd  Random aRandom       if   aStart  gt  aEnd           throw new IllegalArgumentException  Start cannot exceed End                 get the range  casting to long to avoid overflow problems     long range    long aEnd -  long aStart   1         compute a fraction of the range  0  lt   frac  lt  range     long fraction    long  range   aRandom nextDouble         int randomNumber     int  fraction   aStart           log  Generated       randomNumber          private static void log String aMessage       System out println aMessage            An example run of this class    Generating random integers in the range 1  10  Generated   9 Generated   3 Generated   3 Generated   9 Generated   4 Generated   1 Generated   3 Generated   9 Generated   10 Generated   10 Done

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Random number from the range  min  max  inclusive   int randomFromMinToMaxInclusive   ThreadLocalRandom current            nextInt min  max   1

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In Java 1 7 or later  the standard way to do this is as follows   import java util concurrent ThreadLocalRandom      nextInt is normally exclusive of the top value     so add 1 to make it inclusive int randomNum   ThreadLocalRandom current   nextInt min  max   1     See the relevant JavaDoc   This approach has the advantage of not needing to explicitly initialize a java util Random instance  which can be a source of confusion and error if used inappropriately   However  conversely there is no way to explicitly set the seed so it can be difficult to reproduce results in situations where that is useful such as testing or saving game states or similar   In those situations  the pre-Java 1 7 technique shown below can be used   Before Java 1 7  the standard way to do this is as follows   import java util Random          Returns a pseudo-random number between min and max  inclusive     The difference between min and max can be at most     lt code gt Integer MAX VALUE - 1 lt  code gt          param min Minimum value     param max Maximum value   Must be greater than min      return Integer between min and max  inclusive      see java util Random nextInt int      public static int randInt int min  int max            NOTE  This will  intentionally  not run as written so that folks        copy-pasting have to think about how to initialize their        Random instance   Initialization of the Random instance is outside        the main scope of the question  but some decent options are to have        a field that is initialized once and then re-used as needed or to        use ThreadLocalRandom  if using at least Java 1 7                  In particular  do NOT do  Random rand   new Random    here or you        will get not very good   not very random results      Random rand          nextInt is normally exclusive of the top value         so add 1 to make it inclusive     int randomNum   rand nextInt  max - min    1    min       return randomNum      See the relevant JavaDoc   In practice  the java util Random class is often preferable to java lang Math random     In particular  there is no need to reinvent the random integer generation wheel when there is a straightforward API within the standard library to accomplish the task

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Use   minimum   rn nextInt maxValue - minvalue   1

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This is the easy way to do this   import java util Random  class Example      public static void main String args               -To test-         for int i   1  i lt 20   i                 System out print randomnumber                                       int randomnumber   randomnumber                public static int randomnumber            Random rand   new Random            int randomNum   rand nextInt 6    5           return randomNum            In there 5 is the starting point of random numbers  6 is the range including number 5

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ThreadLocalRandom equivalent of class java util Random for multithreaded environment  Generating a random number is carried out locally in each of the threads  So we have a better performance by reducing the conflicts    int rand   ThreadLocalRandom current   nextInt x y     x y - intervals e g   1 10

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I will simply state what is wrong with the solutions provided by the question and why the errors    Solution 1   randomNum   minimum    int  Math random   maximum      Problem  randomNum is assigned values numbers bigger than maximum   Explanation  Suppose our minimum is 5  and your maximum is 10  Any value from Math random   greater than 0 6 will make the expression evaluate to 6 or greater  and adding 5 makes it greater than 10  your maximum   The problem is you are multiplying the random number by the maximum  which generates a number almost as big as the maximum  and then adding the minimum  Unless the minimum is 1  it s not correct  You have to switch to  as mentioned in other answers  randomNum   minimum    int  Math random    maximum-minimum 1     The  1 is because Math random   will never return 1 0   Solution 2   Random rn   new Random    int n   maximum - minimum   1  int i   rn nextInt     n  randomNum    minimum   i    Your problem here is that     may return a negative number if the first term is smaller than 0  Since rn nextInt   returns negative values with  50  chance  you will also not get the expected result   This  was  however  almost perfect  You just had to look a bit further down the Javadoc  nextInt int n   With that method available  doing  Random rn   new Random    int n   maximum - minimum   1  int i   rn nextInt n   randomNum    minimum   i    Would also return the desired result

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Let us take an example   Suppose I wish to generate a number between 5-10   int max   10  int min   5  int diff   max - min  Random rn   new Random    int i   rn nextInt diff   1   i    min  System out print  The Random Number is     i     Let us understand this             Initialize max with highest value and min with the lowest value            Now  we need to determine how many possible values can be obtained  For this example  it would be                  5  6  7  8  9  10               So  count of this would be max - min   1                   i e  10 - 5   1   6               The random number will generate a number between 0-5                   i e  0  1  2  3  4  5               Adding the min value to the random number would produce                  5  6  7  8  9  10                     Hence we obtain the desired range

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I am thinking to linearly normalize the generated random numbers into desired range by using the following  Let x be a random number  let a and b be the minimum and maximum range of desired normalized number   Then below is just a very simple code snipplet to test the range produced by the linear mapping   public static void main String   args        int a   100      int b   1000      int lowest   b      int highest   a      int count   100000      Random random   new Random        for  int i   0  i  lt  count  i              int nextNumber    int    Math abs random nextDouble       b - a      a          if  nextNumber  lt  a    nextNumber  gt  b                System err println  number not in range      nextNumber                     else               System out println nextNumber                     if  nextNumber  lt  lowest                lowest   nextNumber                    if  nextNumber  gt  highest                highest   nextNumber                      System out println  Produced     count     numbers from     lowest                 to     highest

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You can either use the Random class to generate a random number and then use the  nextInt maxNumber  to generate a random number  The maxNumber is the number that you want the maximum when generating a random number  Please remember though  that the Random class gives you the numbers 0 through maxNumber-1     Random r   new Random    int i   r nextInt      Another way to do this is to use the Math Random   class which many classes in schools require you to use because it is more efficient and you don t have to declare a new Random object  To get a random number using Math Random   you type in   Math random      max - min    min

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I wonder if any of the random number generating methods provided by an Apache Commons Math library would fit the bill    For example  RandomDataGenerator nextInt or RandomDataGenerator nextLong

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Here s a helpful class to generate random ints in a range with any combination of inclusive exclusive bounds   import java util Random   public class RandomRange extends Random       public int nextIncInc int min  int max            return nextInt max - min   1    min             public int nextExcInc int min  int max            return nextInt max - min    1   min             public int nextExcExc int min  int max            return nextInt max - min - 1    1   min             public int nextIncExc int min  int max            return nextInt max - min    min

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ThreadLocalRandom equivalent of class java util Random for multithreaded environment  Generating a random number is carried out locally in each of the threads  So we have a better performance by reducing the conflicts    int rand   ThreadLocalRandom current   nextInt x y     x y - intervals e g   1 10

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Use java util for Random for general use   You can define your minimum and maximum range to get those results   Random rand new Random    rand nextInt  max 1  - min    min

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Making the following change in Attempt 1 should do the work -   randomNum   minimum    int  Math random      maximum - minimum       Check this for working code

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I found this example Generate random numbers       This example generates random integers in a specific range    import java util Random       Generate random integers in a certain range     public final class RandomRange      public static final void main String    aArgs       log  Generating random integers in the range 1  10          int START   1      int END   10      Random random   new Random        for  int idx   1  idx  lt   10    idx         showRandomInteger START  END  random              log  Done            private static void showRandomInteger int aStart  int aEnd  Random aRandom       if   aStart  gt  aEnd           throw new IllegalArgumentException  Start cannot exceed End                 get the range  casting to long to avoid overflow problems     long range    long aEnd -  long aStart   1         compute a fraction of the range  0  lt   frac  lt  range     long fraction    long  range   aRandom nextDouble         int randomNumber     int  fraction   aStart           log  Generated       randomNumber          private static void log String aMessage       System out println aMessage            An example run of this class    Generating random integers in the range 1  10  Generated   9 Generated   3 Generated   3 Generated   9 Generated   4 Generated   1 Generated   3 Generated   9 Generated   10 Generated   10 Done

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With java-8 they introduced the method ints int randomNumberOrigin  int randomNumberBound  in the Random class    For example if you want to generate five random integers  or a single one  in the range  0  10   just do   Random r   new Random    int   fiveRandomNumbers   r ints 5  0  11  toArray    int randomNumber   r ints 1  0  11  findFirst   getAsInt      The first parameter indicates just the size of the IntStream generated  which is the overloaded method of the one that produces an unlimited IntStream    If you need to do multiple separate calls  you can create an infinite primitive iterator from the stream   public final class IntRandomNumberGenerator        private PrimitiveIterator OfInt randomIterator                  Initialize a new random number generator that generates        random numbers in the range  min  max          param min - the min value  inclusive          param max - the max value  inclusive              public IntRandomNumberGenerator int min  int max            randomIterator   new Random   ints min  max   1  iterator                          Returns a random number in the range  min  max          return a random number in the range  min  max              public int nextInt             return randomIterator nextInt              You can also do it for double and long values  I hope it helps

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Say you want range between 0-9  0 is minimum and 9 is maximum  The below function will print anything between 0 and 9  It s the same for all ranges   public static void main String   args        int b   randomNumberRange 0  9       int d   randomNumberRange  100  200       System out println  value of b is     b       System out println  value of d is     d      public static int randomNumberRange int min  int max        int n    max   1 - min    min      return  int   Math random     n

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You can edit your second code example to   Random rn   new Random    int range   maximum - minimum   1  int randomNum    rn nextInt range    minimum

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You can do as below  import java util Random  public class RandomTestClass        public static void main String   args            Random r   new Random            int max  min          Scanner scanner   new Scanner System in           System out println  quot Enter maximum value    quot            max   scanner nextInt            System out println  quot Enter minimum value    quot            min   scanner nextInt            int randomNum          randomNum   r nextInt max    min          System out println  quot Random Number    quot    randomNum

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Generate a random number for the difference of min and max by using the nextint n  method and then add min number to the result   Random rn   new Random    int result   rn nextInt max - min   1    min  System out println result

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This will generate Random numbers list with range  Min - Max  with no duplicate   generateRandomListNoDuplicate 1000  8000  500     Add this method   private void generateRandomListNoDuplicate int min  int max  int totalNoRequired        Random rng   new Random        Set lt Integer gt  generatedList   new LinkedHashSet lt  gt         while  generatedList size    lt  totalNoRequired            Integer radnomInt   rng nextInt max - min   1    min          generatedList add radnomInt             Hope this will help you

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I wonder if any of the random number generating methods provided by an Apache Commons Math library would fit the bill    For example  RandomDataGenerator nextInt or RandomDataGenerator nextLong

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I use this              param min - The minimum        param max - The maximum        return A random double between these numbers  inclusive the minimum and maximum          public static double getRandom double min  double max       return  Math random      max   1 - min     min       You can cast it to an Integer if you want

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With java-8 they introduced the method ints int randomNumberOrigin  int randomNumberBound  in the Random class    For example if you want to generate five random integers  or a single one  in the range  0  10   just do   Random r   new Random    int   fiveRandomNumbers   r ints 5  0  11  toArray    int randomNumber   r ints 1  0  11  findFirst   getAsInt      The first parameter indicates just the size of the IntStream generated  which is the overloaded method of the one that produces an unlimited IntStream    If you need to do multiple separate calls  you can create an infinite primitive iterator from the stream   public final class IntRandomNumberGenerator        private PrimitiveIterator OfInt randomIterator                  Initialize a new random number generator that generates        random numbers in the range  min  max          param min - the min value  inclusive          param max - the max value  inclusive              public IntRandomNumberGenerator int min  int max            randomIterator   new Random   ints min  max   1  iterator                          Returns a random number in the range  min  max          return a random number in the range  min  max              public int nextInt             return randomIterator nextInt              You can also do it for double and long values  I hope it helps

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As of Java 7  you should no longer use Random  For most uses  the   random number generator of choice is now   ThreadLocalRandom For fork join pools and parallel   streams  use SplittableRandom    Joshua Bloch  Effective Java  Third Edition   Starting from Java 8  For fork join pools and parallel streams  use SplittableRandom that is usually faster  has a better statistical independence and uniformity properties in comparison with Random   To generate a random int in the range  0  1 000    int n   new SplittableRandom   nextInt 0  1 001     To generate a random int 100  array of values in the range  0  1 000    int   a   new SplittableRandom   ints 100  0  1 001  parallel   toArray      To return a Stream of random values   IntStream stream   new SplittableRandom   ints 100  0  1 001

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Note that this approach is more biased and less efficient than a nextInt approach  https   stackoverflow com a 738651 360211  One standard pattern for accomplishing this is   Min    int  Math random       Max - Min    1     The Java Math library function Math random   generates a double value in the range  0 1   Notice this range does not include the 1   In order to get a specific range of values first  you need to multiply by the magnitude of the range of values you want covered    Math random       Max - Min     This returns a value in the range  0 Max-Min   where  Max-Min  is not included   For example  if you want  5 10   you need to cover five integer values so you use  Math random     5   This would return a value in the range  0 5   where 5 is not included   Now you need to shift this range up to the range that you are targeting  You do this by adding the Min value   Min    Math random      Max - Min     You now will get a value in the range  Min Max   Following our example  that means  5 10    5    Math random      10 - 5     But  this still doesn t include Max and you are getting a double value  In order to get the Max value included  you need to add 1 to your range parameter  Max - Min  and then truncate the decimal part by casting to an int  This is accomplished via   Min    int  Math random       Max - Min    1     And there you have it  A random integer value in the range  Min Max   or per the example  5 10    5    int  Math random       10 - 5    1

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As of Java 7  you should no longer use Random  For most uses  the   random number generator of choice is now   ThreadLocalRandom For fork join pools and parallel   streams  use SplittableRandom    Joshua Bloch  Effective Java  Third Edition   Starting from Java 8  For fork join pools and parallel streams  use SplittableRandom that is usually faster  has a better statistical independence and uniformity properties in comparison with Random   To generate a random int in the range  0  1 000    int n   new SplittableRandom   nextInt 0  1 001     To generate a random int 100  array of values in the range  0  1 000    int   a   new SplittableRandom   ints 100  0  1 001  parallel   toArray      To return a Stream of random values   IntStream stream   new SplittableRandom   ints 100  0  1 001

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You can do as below  import java util Random  public class RandomTestClass        public static void main String   args            Random r   new Random            int max  min          Scanner scanner   new Scanner System in           System out println  quot Enter maximum value    quot            max   scanner nextInt            System out println  quot Enter minimum value    quot            min   scanner nextInt            int randomNum          randomNum   r nextInt max    min          System out println  quot Random Number    quot    randomNum

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private static Random random   new Random         public static int getRandomInt int min  int max     return random nextInt max - min   1    min      OR  public static int getRandomInt Random random  int min  int max      return random nextInt max - min   1    min

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You can either use the Random class to generate a random number and then use the  nextInt maxNumber  to generate a random number  The maxNumber is the number that you want the maximum when generating a random number  Please remember though  that the Random class gives you the numbers 0 through maxNumber-1     Random r   new Random    int i   r nextInt      Another way to do this is to use the Math Random   class which many classes in schools require you to use because it is more efficient and you don t have to declare a new Random object  To get a random number using Math Random   you type in   Math random      max - min    min

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Use   minimum   rn nextInt maxValue - minvalue   1

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rand nextInt  max 1  - min    min

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The following snippet will give a random value between 0 and 10000   import java util Random  public class Main       public static void main String   args            Random rand   new Random            System out printf   04d n   rand nextInt 10000

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It can be done by simply doing the statement   Randomizer generate 0 10     min of zero  max of ten   Below is its source-code  Randomizer java  public class Randomizer       public static int generate int min int max            return min    int  Math random       max - min    1              It is just clean and simple

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You can edit your second code example to   Random rn   new Random    int range   maximum - minimum   1  int randomNum    rn nextInt range    minimum

[java] How do I generate random integers within a specific range in Java?

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