How to randomly pick an element from an array

Question

I am looking for solution to pick number randomly from an integer array   For example I have an array new int   1 2 3   how can I pick a number randomly

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You can use the Random generator to generate a random index and return the element at that index     initialization Random generator   new Random    int randomIndex   generator nextInt myArray length   return myArray randomIndex

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You can also use   public static int getRandom int   array        int rnd    int  Math random   array length       return array rnd       Math random   returns an double between 0 0  inclusive  to 1 0  exclusive   Multiplying this with array length gives you a double between 0 0  inclusive  and array length  exclusive    Casting to int will round down giving you and integer between 0  inclusive  and array length-1  inclusive

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You can also try this approach    public static  lt E gt  E   pickRandom  int n E    item            List lt E gt  copy   Arrays asList item           Collections shuffle copy           if  copy size    gt  n                return  E    copy subList 0  n  toArray              else               return  E    copy toArray

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If you are going to be getting a random element multiple times  you want to make sure your random number generator is initialized only once   import java util Random   public class RandArray       private int   items   new int   1 2 3        private Random rand   new Random         public int getRandArrayElement            return items rand nextInt items length              If you are picking random array elements that need to be unpredictable  you should use java security SecureRandom rather than Random    That ensures that if somebody knows the last few picks  they won t have an advantage in guessing the next one   If you are looking to pick a random number from an Object array using generics  you could define a method for doing so  Source Avinash R in Random element from string array    import java util Random   public class RandArray       private static Random rand   new Random         private static  lt T gt  T randomFrom T    items              return items rand nextInt items length

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With Java 7  one can use ThreadLocalRandom   A random number generator isolated to the current thread  Like the global Random generator used by the Math class  a ThreadLocalRandom is initialized with an internally generated seed that may not otherwise be modified  When applicable  use of ThreadLocalRandom rather than shared Random objects in concurrent programs will typically encounter much less overhead and contention  Use of ThreadLocalRandom is particularly appropriate when multiple tasks  for example  each a ForkJoinTask  use random numbers in parallel in thread pools   public static int getRandomElement int   arr       return arr ThreadLocalRandom current   nextInt arr length         Example Usage  int   nums    1  2  3  4   int randNum   getRandomElement nums   System out println randNum    A generic version can also be written  but it will not work for primitive arrays  public static  lt T gt  T getRandomElement T   arr      return arr ThreadLocalRandom current   nextInt arr length         Example Usage  String   strs     quot aa quot    quot bb quot    quot cc quot    String randStr   getRandomElement strs   System out println randStr

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package io github baijifeilong tmp   import java util concurrent ThreadLocalRandom  import java util stream Stream          Created by BaiJiFeiLong gmail com at 2019 1 3   7 34     public class Bar       public static void main String   args            Stream generate    - gt  null  limit 10  forEach   - gt                System out println new String    hello    world   ThreadLocalRandom current   nextInt 2

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public static int getRandom int   array        int rnd   new Random   nextInt array length       return array rnd

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Use the Random class   int getRandomNumber int   arr      return arr  new Random    nextInt arr length

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use java util Random to generate a random number between 0 and array length  random number  and then use the random number to get the integer  array random number

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Since you have java 8  another solution is to use Stream API   new Random   ints 1  500  limit 500  forEach p - gt  System out println list p       Where 1 is the lowest int generated  inclusive  and 500 is the highest  exclusive   limit means that your stream will have a length of 500    int   list   new int    1 2 3 4 5 6    new Random   ints 0  list length  limit 10  forEach p - gt  System out println list p        Random is from java util package

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Take a look at this question   How do I generate random integers within a specific range in Java   You will want to generate a random number from 0 to your integers length - 1  Then simply get your int from your array   myArray myRandomNumber

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package workouts   import java util Random              author Muthu     public class RandomGenerator       public static void main String   args         for int i 0 i lt 5 i              rndFunc                       public static void rndFunc               int  a  new int   1 2 3              Random rnd  new Random               System out println a rnd nextInt a length

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Java has a Random class in the java util package  Using it you can do the following   Random rnd   new Random    int randomNumberFromArray   array rnd nextInt 3      Hope this helps

[java] How to randomly pick an element from an array

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