Get random boolean in Java

Question

Okay  I implemented this SO question to my code  Return True or False Randomly  But  I have strange behavior  I need to run ten instances simultaneously  where every instance returns true or false just once per run  And surprisingly  no matter what I do  every time i get just false  Is there something to improve the method so I can have at least roughly 50  chance to get true     To make it more understandable  I have my application builded to JAR file which is then run via batch command   java -jar my-program jar  pause   Content of the program - to make it as simple as possible   public class myProgram       public static boolean getRandomBoolean             return Math random    lt  0 5             I tried another approaches here  still the same result            public static void main String   args            System out println getRandomBoolean                 If I open 10 command lines and run it  I get false as result every time

User · Answer

You could also try nextBoolean  -Method Here is an example  http   www tutorialspoint com java util random nextboolean htm

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you could get your clock   value and check if it is odd or even  I dont know if it is  50 of true  And you can custom-create your random function   static double  s System nanoTime     in the instantiating of main applet public static double randoom      s  double    555555555  s  444444  100000   double 100000         return s      numbers 55555   and 444   are the big numbers to get a wide range function please ignore that skype icon  D

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Why not use the Random class  which has a method nextBoolean   import java util Random       Generate 10 random booleans     public final class MyProgram      public static final void main String    args        Random randomGenerator   new Random        for  int idx   1  idx  lt   10    idx         boolean randomBool   randomGenerator nextBoolean          System out println  Generated       randomBool

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You can also make two random integers and verify if they are the same  this gives you more control over the probabilities   Random rand   new Random      Declare a range to manage random probability  In this example  there is a 50  chance of being true   int range   2    Generate 2 random integers   int a   rand nextInt range   int b   rand nextInt range     Then simply compare return the value   return a    b     I also have a class you can use  RandomRange java

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Words in a text are always a source of randomness  Given a certain word  nothing can be inferred about the next word  For each word  we can take the ASCII codes of its letters  add those codes to form a number  The parity of this number is a good candidate for a random boolean   Possible drawbacks    this strategy is based upon using a text file as a source for the words  At some point   the end of the file will be reached  However  you can estimate how many times you are expected to call the randomBoolean   function from your app  If you will need to call it about 1 million times  then a text file with 1 million words will be enough   As a correction  you can use a stream of data from a live source like an online newspaper  using some statistical analysis of the common phrases and idioms in a language  one can estimate the next word in a phrase   given the first words of the phrase  with some degree of accuracy  But statistically  these cases are rare  when we can accuratelly  predict the next word  So  in most cases  the next word is independent on the previous words   package p01   import java io File  import java nio file Files  import java nio file Paths   public class Main    String words    int currentIndex 0   public static String readFileAsString  throws Exception           String data            File file   new File  the comedy of errors          System out println file exists         data   new String Files readAllBytes Paths get file getName            return data         public void init   throws Exception       String data   readFileAsString         words   data split    t             r   n         public String getNextWord   throws Exception       if currentIndex gt words length-1          throw new Exception  out of words  reached end of file         String currentWord   words currentIndex       currentIndex         while currentWord isEmpty                  currentWord   words currentIndex           currentIndex               return currentWord     public boolean getNextRandom   throws Exception       String nextWord   getNextWord        int asciiSum   0       for  int i   0  i  lt  nextWord length    i             char c   nextWord charAt i                   asciiSum   asciiSum    int  c             System out println nextWord  -  asciiSum        return  asciiSum 2  1       public static void main String args    throws Exception       Main m   new Main        m init        while true                System out println m getNextRandom             Thread sleep 100                 In Eclipse  in the root of my project  there is a file called  the comedy of errors   no extension  - created with  File  New   File   where I pasted some content from here  http   shakespeare mit edu comedy errors comedy errors 1 1 html

User · Answer

I recommend using Random nextBoolean    That being said  Math random    lt  0 5 as you have used works too  Here s the behavior on my machine     cat myProgram java  public class myProgram      public static boolean getRandomBoolean            return Math random    lt  0 5           I tried another approaches here  still the same result          public static void main String   args           System out println getRandomBoolean                 javac myProgram java   java myProgram   java myProgram  java myProgram  java myProgram true false false true   Needless to say  there are no guarantees for getting different values each time  In your case however  I suspect that  A  you re not working with the code you think you are   like editing the wrong file   B  you havn t compiled your different attempts when testing  or  C  you re working with some non-standard broken implementation

User · Answer

You can use the following for an unbiased result   Random random   new Random      For 50  chance of true boolean chance50oftrue    random nextInt 2     0    true   false    Note  random nextInt 2  means that the number 2 is the bound  the counting starts at 0  So we have 2 possible numbers  0 and 1  and hence the probability is 50    If you want to give more probability to your result to be true  or false  you can adjust the above as following    Random random   new Random       For 50  chance of true boolean chance50oftrue    random nextInt 2     0    true   false     For 25  chance of true boolean chance25oftrue    random nextInt 4     0    true   false     For 40  chance of true boolean chance40oftrue    random nextInt 5   lt  2    true   false

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Java 8  Use random generator isolated to the current thread  ThreadLocalRandom nextBoolean       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    java util concurrent ThreadLocalRandom current   nextBoolean

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The easiest way to initialize a random number generator is to use the parameterless constructor  for example  Random generator   new Random      However  in using this constructor you should recognize that algorithmic random number generators are not truly random  they are really algorithms that generate a fixed but random-looking sequence of numbers   You can make it appear more  random  by giving the Random constructor the  seed  parameter  which you can dynamically built by for example using system time in milliseconds  which will always be different

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Have you tried looking at the Java Documentation      Returns the next pseudorandom  uniformly distributed boolean value from this random number generator s sequence     the values true and false are produced with  approximately  equal probability    For example   import java util Random   Random random   new Random    random nextBoolean

[java] Get random boolean in Java

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