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How to generate unique random numbers in java

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instanceof java

Posts: 576
Nickname: instanceof
Registered: Jan, 2015

instanceof java is a java related one.
How to generate unique random numbers in java Posted: Aug 24, 2016 11:54 AM
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This post originated from an RSS feed registered with Java Buzz by instanceof java.
Original Post: How to generate unique random numbers in java
Feed Title: Instance Of Java
Feed URL: http://feeds.feedburner.com/blogspot/TXghwE
Feed Description: Instance of Java. A place where you can learn java in simple way each and every topic covered with many points and sample programs. 		Latest Java Buzz Posts
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  • In java we can generate random number in two ways 
  • By using Random class
  • By using Math.random



Program #1:  Java Example program to generate random numbers using random class within  the range of 1 to 10

  • First we need to create object of java.util.Random class.
  • After creating object of java.util.Random class then we need call nextInt() method by passing range
  • int range = maximum - minimum + 1;
  • int randomNum =  rn.nextInt(range) + minimum;

  1. package com.randomnumbergenerator;

  3. import java.util.Random;
  4. import java.util.Scanner;

  6. public class RandomNumber {

  8. /**
  9. * @Website: www.instanceofjava.com
  10. * @category: how to generate random numbers in java within range
  11. */
  12. public static void main(String[] args) {
  14. Scanner in = new Scanner(System.in);
  15. System.out.println("Enter minimum number");
  16. int minimum=in.nextInt();
  18. System.out.println("Enter maximum number");
  19. int maximum=in.nextInt();
  21. Random rn = new Random();
  22. int range = maximum - minimum + 1;
  23. int randomNum =  rn.nextInt(range) + minimum;
  25. System.out.println("Random Number= "+randomNum);

  27. }

  29. }

Output:

  1. Enter minimum number
  2. 1
  3. Enter maximum number
  4. 10
  5. Random Number= 4


Program #2:  Java Example program to generate random numbers using Math.random  within  the range of 1 to 10

  • By using Math.random() method also we can generate random number in java
  • int randomNum = minimum + (int)(Math.random() * maximum);

  1. package com.randomnumbergenerator;

  3. import java.util.Random;
  4. import java.util.Scanner;

  6. public class RandomNumber {

  8. /**
  9. * @Website: www.instanceofjava.com
  10. * @category: how to generate random numbers in java within range
  11. */
  12. public static void main(String[] args) {
  14. Scanner in = new Scanner(System.in);
  15. System.out.println("Enter minimum number");
  16. int minimum=in.nextInt();
  18. System.out.println("Enter maximum number");
  19. int maximum=in.nextInt();
  20.   
  21.   int randomNum = minimum + (int)(Math.random() * maximum);
  23. System.out.println("Random Number= "+randomNum);

  25. }

  27. }

Output:

  1. Enter minimum number
  2. 1
  3. Enter maximum number
  4. 10
  5. Random Number=5


Program #3:  Java Example program to generate 10 random numbers using Random class  within  the range of 1 to 100 using for loop.

  1. package com.randomnumbergenerator;

  3. import java.util.Random;
  4. import java.util.Scanner;

  6. public class RandomNumber {

  8. /**
  9. * @Website: www.instanceofjava.com
  10. * @category: how to generate random numbers in java within range
  11. */
  12. public static void main(String[] args) {
  14. Random randomNumGenerator = new Random();
  15.  
  16.            for (int idx = 1; idx <= 10; ++idx){
  17.               int randomInt = randomNumGenerator.nextInt(100);
  18.               System.out.println("Random Number= "+randomInt);
  19.  
  20. }       

  22. }

  24. }

Output:

  1. Random Number= 17
  2. Random Number= 3
  3. Random Number= 74
  4. Random Number= 59
  5. Random Number= 81
  6. Random Number= 90
  7. Random Number= 2
  8. Random Number= 32
  9. Random Number= 11
  10. Random Number= 75


random number generator java




How to generate random numbers in java without repetitions

  • lets see how to generate unique random numbers in java
  • By using Collections.shuffle();


Program #4:  Java Example program to generate 4 random numbers using Random class  within  the range of 1 to 100 without duplicate / java generate unique random number between 1 and 100


  1. package com.randomnumbergenerator;


  4. public class RandomNumber {

  6. /**
  7. * @Website: www.instanceofjava.com
  8. * @category: how to generate random numbers in java within range
  9. */
  10. public static void main(String[] args) {
  12.   ArrayList<Integer> list = new ArrayList<Integer>();
  13.             for (int i=1; i<10; i++) {
  14.                 list.add(new Integer(i));
  15.             }
  16.             Collections.shuffle(list);
  17.             for (int i=0; i<4; i++) {
  18.                 System.out.println("Random Number= "+(list.get(i)));
  19.             }
  20. }       

  22. }

  24. }

Output:

  1. Random Number= 7
  2. Random Number= 3
  3. Random Number= 2
  4. Random Number= 9

Program #5:  Java Example program to generate 10 random numbers. random number generator that doesn't repeat java

  1. package com.randomnumbergenerator;


  4. public class RandomNumber {

  6. /**
  7. * @Website: www.instanceofjava.com
  8. * @category: how to generate 10 random numbers in java within range
  9. */
  10.  
  11. public static final int SET_SIZE_REQUIRED = 10;
  12.  public static final int NUMBER_RANGE = 100;
  13.  
  14.  public static void main(String[] args) {
  15.  
  16.             Random random = new Random();
  17.  
  18.             Set set = new HashSet<Integer>(SET_SIZE_REQUIRED);
  19.  
  20.             while(set.size()< SET_SIZE_REQUIRED) {
  21.                 while (set.add(random.nextInt(NUMBER_RANGE)) != true)
  22.                     ;
  23.             }
  24.             assert set.size() == SET_SIZE_REQUIRED;
  25.             System.out.println(set);
  26.         }
  27. }


Output:

  1. [48, 99, 24, 58, 44, 77, 14, 95, 31, 79]

Read: How to generate unique random numbers in java

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