How to generate unique random numbers in java

• 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;
2. 
   
3. import java.util.Random;
4. import java.util.Scanner;
5. 
   
6. public class RandomNumber {
7. 
   
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);
26. 
    
27. }
28. 
    
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;
2. 
   
3. import java.util.Random;
4. import java.util.Scanner;
5. 
   
6. public class RandomNumber {
7. 
   
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);
24. 
    
25. }
26. 
    
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;
2. 
   
3. import java.util.Random;
4. import java.util.Scanner;
5. 
   
6. public class RandomNumber {
7. 
   
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. }       
21. 
    
22. }
23. 
    
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

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;
2. 
   
3. 
   
4. public class RandomNumber {
5. 
   
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. }       
21. 
    
22. }
23. 
    
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;
2. 
   
3. 
   
4. public class RandomNumber {
5. 
   
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. }
28. 
    

Output:

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