Java Tutorial/Development/Random

Create two random number generators with the same seed

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] argv) throws Exception {
   Random rand = new Random();
   long seed = rand.nextLong();
   rand = new Random(seed);
   Random rand2 = new Random(seed);
 }

}</source>

Generate a random array of numbers

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] args) {
   Random r = new Random();
   // generate some random boolean values
   boolean[] booleans = new boolean[10];
   for (int i = 0; i < booleans.length; i++) {
     booleans[i] = r.nextBoolean();
   }
   for (boolean b : booleans) {
     System.out.print(b + ", ");
   }
   // generate a uniformly distributed int random numbers
   int[] integers = new int[10];
   for (int i = 0; i < integers.length; i++) {
     integers[i] = r.nextInt();
   }
   for (int i : integers) {
     System.out.print(i + ", ");
   }
   // generate a uniformly distributed float random numbers
   float[] floats = new float[10];
   for (int i = 0; i < floats.length; i++) {
     floats[i] = r.nextFloat();
   }
   for (float f : floats) {
     System.out.print(f + ", ");
   }
   // generate a Gaussian normally distributed random numbers
   double[] gaussians = new double[10];
   for (int i = 0; i < gaussians.length; i++) {
     gaussians[i] = r.nextGaussian();
   }
   for (double d : gaussians) {
     System.out.print(d + ", ");
   }
 }

}</source>

Generating Random integer Numbers

   <source lang="java">

import java.util.Random; public class MainClass {

 public static void main(String[] args) {
   Random diceValues = new Random();
   System.out.println(diceValues.nextInt(6));
   System.out.println(diceValues.nextInt(6));
 }

}</source>

5
3

Operations for random Strings

   <source lang="java">

/*

* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
* 
*      http://www.apache.org/licenses/LICENSE-2.0
* 
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

import java.util.Random; /**

* Operations for random Strings.
* Currently private high surrogate characters are ignored. 
* These are unicode characters that fall between the values 56192 (db80)
* and 56319 (dbff) as we don"t know how to handle them. 
* High and low surrogates are correctly dealt with - that is if a 
* high surrogate is randomly chosen, 55296 (d800) to 56191 (db7f) 
* then it is followed by a low surrogate. If a low surrogate is chosen, 
* 56320 (dc00) to 57343 (dfff) then it is placed after a randomly 
* chosen high surrogate. 
*
* @author 
* @author Stephen Colebourne
* @author Gary Gregory
* @author Phil Steitz
* @since 1.0
* @version $Id: RandomStringUtils.java 471626 2006-11-06 04:02:09Z bayard $
*/

public class RandomStringUtils {

   /**
    * Random object used by random method. This has to be not local
    * to the random method so as to not return the same value in the 
    * same millisecond.
    */
   private static final Random RANDOM = new Random();
   /**
    * RandomStringUtils instances should NOT be constructed in
    * standard programming. Instead, the class should be used as
    * RandomStringUtils.random(5);.
    *
    * This constructor is public to permit tools that require a JavaBean instance
    * to operate.
    */
   public RandomStringUtils() {
     super();
   }
   // Random
   //-----------------------------------------------------------------------
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of all characters.
    *
    * @param count  the length of random string to create
    * @return the random string
    */
   public static String random(int count) {
       return random(count, false, false);
   }
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of characters whose
    * ASCII value is between 32 and 126 (inclusive).
    *
    * @param count  the length of random string to create
    * @return the random string
    */
   public static String randomAscii(int count) {
       return random(count, 32, 127, false, false);
   }
   
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of alphabetic
    * characters.
    *
    * @param count  the length of random string to create
    * @return the random string
    */
   public static String randomAlphabetic(int count) {
       return random(count, true, false);
   }
   
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of alpha-numeric
    * characters.
    *
    * @param count  the length of random string to create
    * @return the random string
    */
   public static String randomAlphanumeric(int count) {
       return random(count, true, true);
   }
   
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of numeric
    * characters.
    *
    * @param count  the length of random string to create
    * @return the random string
    */
   public static String randomNumeric(int count) {
       return random(count, false, true);
   }
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of alpha-numeric
    * characters as indicated by the arguments.
    *
    * @param count  the length of random string to create
    * @param letters  if true, generated string will include
    *  alphabetic characters
    * @param numbers  if true, generated string will include
    *  numeric characters
    * @return the random string
    */
   public static String random(int count, boolean letters, boolean numbers) {
       return random(count, 0, 0, letters, numbers);
   }
   
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of alpha-numeric
    * characters as indicated by the arguments.
    *
    * @param count  the length of random string to create
    * @param start  the position in set of chars to start at
    * @param end  the position in set of chars to end before
    * @param letters  if true, generated string will include
    *  alphabetic characters
    * @param numbers  if true, generated string will include
    *  numeric characters
    * @return the random string
    */
   public static String random(int count, int start, int end, boolean letters, boolean numbers) {
       return random(count, start, end, letters, numbers, null, RANDOM);
   }
   /**
    * Creates a random string based on a variety of options, using
    * default source of randomness.
    *
    * This method has exactly the same semantics as
    * {@link #random(int,int,int,boolean,boolean,char[],Random)}, but
    * instead of using an externally supplied source of randomness, it uses
    * the internal static {@link Random} instance.
    *
    * @param count  the length of random string to create
    * @param start  the position in set of chars to start at
    * @param end  the position in set of chars to end before
    * @param letters  only allow letters?
    * @param numbers  only allow numbers?
    * @param chars  the set of chars to choose randoms from.
    *  If null, then it will use the set of all chars.
    * @return the random string
    * @throws ArrayIndexOutOfBoundsException if there are not
    *  (end - start) + 1 characters in the set array.
    */
   public static String random(int count, int start, int end, boolean letters, boolean numbers, char[] chars) {
       return random(count, start, end, letters, numbers, chars, RANDOM);
   }
   /**
    * Creates a random string based on a variety of options, using
    * supplied source of randomness.
    *
    * If start and end are both 0, start and end are set
    * to " " and "z", the ASCII printable
    * characters, will be used, unless letters and numbers are both
    * false, in which case, start and end are set to
    * 0 and Integer.MAX_VALUE.
    *
    * If set is not null, characters between start and
    * end are chosen.
    *
    * This method accepts a user-supplied {@link Random}
    * instance to use as a source of randomness. By seeding a single 
    * {@link Random} instance with a fixed seed and using it for each call,
    * the same random sequence of strings can be generated repeatedly
    * and predictably.
    *
    * @param count  the length of random string to create
    * @param start  the position in set of chars to start at
    * @param end  the position in set of chars to end before
    * @param letters  only allow letters?
    * @param numbers  only allow numbers?
    * @param chars  the set of chars to choose randoms from.
    *  If null, then it will use the set of all chars.
    * @param random  a source of randomness.
    * @return the random string
    * @throws ArrayIndexOutOfBoundsException if there are not
    *  (end - start) + 1 characters in the set array.
    * @throws IllegalArgumentException if count < 0.
    * @since 2.0
    */
   public static String random(int count, int start, int end, boolean letters, boolean numbers,
                               char[] chars, Random random) {
       if (count == 0) {
           return "";
       } else if (count < 0) {
           throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
       }
       if ((start == 0) && (end == 0)) {
           end = "z" + 1;
           start = " ";
           if (!letters && !numbers) {
               start = 0;
               end = Integer.MAX_VALUE;
           }
       }
       char[] buffer = new char[count];
       int gap = end - start;
       while (count-- != 0) {
           char ch;
           if (chars == null) {
               ch = (char) (random.nextInt(gap) + start);
           } else {
               ch = chars[random.nextInt(gap) + start];
           }
           if ((letters && Character.isLetter(ch))
               || (numbers && Character.isDigit(ch))
               || (!letters && !numbers)) 
           {
               if(ch >= 56320 && ch <= 57343) {
                   if(count == 0) {
                       count++;
                   } else {
                       // low surrogate, insert high surrogate after putting it in
                       buffer[count] = ch;
                       count--;
                       buffer[count] = (char) (55296 + random.nextInt(128));
                   }
               } else if(ch >= 55296 && ch <= 56191) {
                   if(count == 0) {
                       count++;
                   } else {
                       // high surrogate, insert low surrogate before putting it in
                       buffer[count] = (char) (56320 + random.nextInt(128));
                       count--;
                       buffer[count] = ch;
                   }
               } else if(ch >= 56192 && ch <= 56319) {
                   // private high surrogate, no effing clue, so skip it
                   count++;
               } else {
                   buffer[count] = ch;
               }
           } else {
               count++;
           }
       }
       return new String(buffer);
   }
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of characters
    * specified.
    *
    * @param count  the length of random string to create
    * @param chars  the String containing the set of characters to use,
    *  may be null
    * @return the random string
    * @throws IllegalArgumentException if count < 0.
    */
   public static String random(int count, String chars) {
       if (chars == null) {
           return random(count, 0, 0, false, false, null, RANDOM);
       }
       return random(count, chars.toCharArray());
   }
   /**
    * Creates a random string whose length is the number of characters
    * specified.
    *
    * Characters will be chosen from the set of characters specified.
    *
    * @param count  the length of random string to create
    * @param chars  the character array containing the set of characters to use,
    *  may be null
    * @return the random string
    * @throws IllegalArgumentException if count < 0.
    */
   public static String random(int count, char[] chars) {
       if (chars == null) {
           return random(count, 0, 0, false, false, null, RANDOM);
       }
       return random(count, 0, chars.length, false, false, chars, RANDOM);
   }
   

}</source>

Random boolean

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] argv) throws Exception {
   Random rand = new Random();
   boolean b = rand.nextBoolean();
   long l = rand.nextLong();
   float f = rand.nextFloat(); // 0.0 <= f < 1.0
   double d = rand.nextDouble(); // 0.0 <= d < 1.0
 }

}</source>

Random bytes

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] argv) throws Exception {
   Random rand = new Random();
   byte[] bytes = new byte[5];
   rand.nextBytes(bytes);
 }

}</source>

Random double type number

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] argv) throws Exception {
   Random rand = new Random();
   boolean b = rand.nextBoolean();
   long l = rand.nextLong();
   float f = rand.nextFloat(); // 0.0 <= f < 1.0
   double d = rand.nextDouble(); // 0.0 <= d < 1.0
 }

}</source>

Random float type number

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] argv) throws Exception {
   Random rand = new Random();
   boolean b = rand.nextBoolean();
   long l = rand.nextLong();
   float f = rand.nextFloat(); // 0.0 <= f < 1.0
   double d = rand.nextDouble(); // 0.0 <= d < 1.0
 }

}</source>

Random Gaussian values.

   <source lang="java">

import java.util.Random; class RandDemo {

 public static void main(String args[]) {
   Random r = new Random();
   double val;
   double sum = 0;
   int bell[] = new int[10];
   for (int i = 0; i < 100; i++) {
     val = r.nextGaussian();
     sum += val;
     double t = -2;
     for (int x = 0; x < 10; x++, t += 0.5)
       if (val < t) {
         bell[x]++;
         break;
       }
   }
   System.out.println("Average of values: " + (sum / 100));
   for (int i = 0; i < 10; i++) {
     for (int x = bell[i]; x > 0; x--)
       System.out.print("*");
     System.out.println();
   }
 }

}</source>

Random integers that range from from 0 to n

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] argv) throws Exception {
   Random rand = new Random();
   int n = 10;
   int i = rand.nextInt(n + 1);
   System.out.println(i);
 }

}</source>

Random long type number

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] argv) throws Exception {
   Random rand = new Random();
   boolean b = rand.nextBoolean();
   long l = rand.nextLong();
   float f = rand.nextFloat(); // 0.0 <= f < 1.0
   double d = rand.nextDouble(); // 0.0 <= d < 1.0
 }

}</source>

Random.nextInt(n) returns a distributed int value between 0 (inclusive) and n (exclusive).

   <source lang="java">

// random number between 0 AND 10 import java.util.Random; public class Main {

 public static void main(String[] argv) {
   Random r = new Random();
   int randint = r.nextInt(10);
   System.out.println(randint);
 }

}</source>

Random number between 0 AND 10

   <source lang="java">

import java.util.Random; public class Main {

 public static void main(String[] argv) {
   Random r = new Random();
   int randint = Math.abs(r.nextInt()) % 11;
   System.out.println(randint);
 }

}</source>

Random numbers between 0.0 and 1.0

   <source lang="java">

public class Main {

 public static void main(String[] args) {
   
   for (int i = 0; i < 5; i++){
     System.out.println("Random Number [" + (i + 1) + "] : " + Math.random());
   }
 }

}</source>

Roll a six-sided die imes

   <source lang="java">

import java.util.Random; public class MainClass {

  public static void main( String args[] )
  {
     Random randomNumbers = new Random(); // random number generator
     int frequency1 = 0; // count of 1s rolled
     int frequency2 = 0; // count of 2s rolled
     int frequency3 = 0; // count of 3s rolled
     int frequency4 = 0; // count of 4s rolled
     int frequency5 = 0; // count of 5s rolled
     int frequency6 = 0; // count of 6s rolled
     int face; // stores most recently rolled value
  
     // summarize results of 6000 rolls of a die
     for ( int roll = 1; roll <= 6000; roll++ ) 
     {
        face = 1 + randomNumbers.nextInt( 6 ); // number from 1 to 6
  
        // determine roll value 1-6 and increment appropriate counter
        switch ( face ) 
        {   
           case 1:
              ++frequency1; // increment the 1s counter
              break; 
           case 2:
              ++frequency2; // increment the 2s counter
              break;
           case 3:
              ++frequency3; // increment the 3s counter
              break;
           case 4:
              ++frequency4; // increment the 4s counter
              break;
           case 5:
              ++frequency5; // increment the 5s counter
              break;
           case 6:
              ++frequency6; // increment the 6s counter
              break; // optional at end of switch
        }
     }
     System.out.println( "Face\tFrequency" ); // output headers
     System.out.printf( "1\t%d\n2\t%d\n3\t%d\n4\t%d\n5\t%d\n6\t%d\n",
        frequency1, frequency2, frequency3, frequency4,
        frequency5, frequency6 );
  }

}</source>

Face  Frequency
1 1005
2 1028
3 1027
4 989
5 994
6 957