How to generate random integers in Java-javaTutorial-php.cn

How to generate random integers in Java

王林

Release： 2023-05-20 09:28:28

forward

1406 people have browsed it

1. java.util.Random

This Random().nextInt(int bound) will generate a random integer from 0 (inclusive) to bound (exclusive).

(1) Code snippet

For getRandomNumberInRange(5, 10), this will generate a random integer between 5 (inclusive) and 10 (inclusive).

private static int getRandomNumberInRange(int min, int max) {
		if (min >= max) {
			throw new IllegalArgumentException("max must be greater than min");
		}
		Random r = new Random();
		return r.nextInt((max - min) + 1) + min;
	}

Copy after login

(2) What is (max – min) 1) min?

The above formula will generate a random integer between min (inclusive) and max (inclusive) .

//Random().nextInt(int bound) = Random integer from 0 (inclusive) to bound (exclusive)	
	//1. nextInt(range) = nextInt(max - min)
	new Random().nextInt(5);  // [0...4] [min = 0, max = 4]
	new Random().nextInt(6);  // [0...5]
	new Random().nextInt(7);  // [0...6]
	new Random().nextInt(8);  // [0...7]
	new Random().nextInt(9);  // [0...8]
	new Random().nextInt(10); // [0...9]			
	new Random().nextInt(11); // [0...10]	
	//2. To include the last value (max value) = (range + 1)
	new Random().nextInt(5 + 1)  // [0...5] [min = 0, max = 5]
	new Random().nextInt(6 + 1)  // [0...6]
	new Random().nextInt(7 + 1)  // [0...7]
	new Random().nextInt(8 + 1)  // [0...8]
	new Random().nextInt(9 + 1)  // [0...9]
	new Random().nextInt(10 + 1) // [0...10]			
	new Random().nextInt(11 + 1) // [0...11]	
	//3. To define a start value (min value) in a range,
	//   For example, the range should start from 10 = (range + 1) + min
	new Random().nextInt(5 + 1)  + 10 // [0...5]  + 10 = [10...15]
	new Random().nextInt(6 + 1)  + 10 // [0...6]  + 10 = [10...16]
	new Random().nextInt(7 + 1)  + 10 // [0...7]  + 10 = [10...17]
	new Random().nextInt(8 + 1)  + 10 // [0...8]  + 10 = [10...18]
	new Random().nextInt(9 + 1)  + 10 // [0...9]  + 10 = [10...19]
	new Random().nextInt(10 + 1) + 10 // [0...10] + 10 = [10...20]
	new Random().nextInt(11 + 1) + 10 // [0...11] + 10 = [10...21]	
	// Range = (max - min)
	// So, the final formula is ((max - min) + 1) + min	
	//4. Test [10...30]
	// min = 10 , max = 30, range = (max - min)
	new Random().nextInt((max - min) + 1) + min
	new Random().nextInt((30 - 10) + 1) + 10
	new Random().nextInt((20) + 1) + 10
	new Random().nextInt(21) + 10    //[0...20] + 10 = [10...30]	
	//5. Test [15...99]
	// min = 15 , max = 99, range = (max - min)
	new Random().nextInt((max - min) + 1) + min
	new Random().nextInt((99 - 15) + 1) + 15
	new Random().nextInt((84) + 1) + 15
	new Random().nextInt(85) + 15    //[0...84] + 15 = [15...99]	
	//Done, understand?

Copy after login

(3) Generate a complete example of 10 random integers in the range between 5 (inclusive) and 10 (inclusive).

package com.mkyong.example.test;
import java.util.Random;
public class TestRandom {
	public static void main(String[] args) {
		for (int i = 0; i < 10; i++) {
			System.out.println(getRandomNumberInRange(5, 10));
		}
	}
	private static int getRandomNumberInRange(int min, int max) {
		if (min >= max) {
			throw new IllegalArgumentException("max must be greater than min");
		}
		Random r = new Random();
		return r.nextInt((max - min) + 1) + min;
	}
}

Copy after login

Output

7
6
10
8
9
5
7
10
8
5

2. Math.Random

This Math.random() gives a random double value from 0.0 (inclusive) to 1.0 (exclusive) .

(1) Code snippet. Referring to 1.2, it's more or less the same formula.

(int)(Math.random() * ((max - min) 1)) min

(2) generates 16 (inclusive) to 20 (inclusive Complete example of 10 random integers in the range ).

package com.mkyong.example.test;
public class TestRandom {
	public static void main(String[] args) {
		for (int i = 0; i < 10; i++) {
			System.out.println(getRandomNumberInRange(16, 20));
		}
	}
	private static int getRandomNumberInRange(int min, int max) {
		if (min >= max) {
			throw new IllegalArgumentException("max must be greater than min");
		}
		return (int)(Math.random() * ((max - min) + 1)) + min;
	}
}

Copy after login

Output

17
16
20
19
20
20
20
17
20
16

3. Java 8 Random.ints

In Java 8, a new method java.util.Random

public IntStream ints(int randomNumberOrigin, int randomNumberBound)
	public IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound)

Copy after login

This Random. ints(int origin, int bound) or Random.ints(int min, int max) generates a random integer from origin (inclusive) to bound (exclusive).

(1) Code snippet.

private static int getRandomNumberInRange(int min, int max) {	
		Random r = new Random();
		return r.ints(min, (max + 1)).findFirst().getAsInt();
	}

Copy after login

(2) Generate a complete example of 10 random integers in the range 33 (inclusive) to 38 (inclusive).

package com.mkyong.form.test;
import java.util.Random;
public class TestRandom {
	public static void main(String[] args) {
		for (int i = 0; i < 10; i++) {
			System.out.println(getRandomNumberInRange(33, 38));
		}
	}
	private static int getRandomNumberInRange(int min, int max) {	
		Random r = new Random();
		return r.ints(min, (max + 1)).limit(1).findFirst().getAsInt();		
	}	
}

Copy after login

Output

34
35
37
33
38
37
34
35
36
37

(3) Extra, for your own reference.

Generate a random integer in the range between 33 (inclusive) and 38 (exclusive), with a stream size of 10. and print out the output with forEach.

//Java 8 only
	new Random().ints(10, 33, 38).forEach(System.out::println);

Copy after login

34
37
37
34
34
35
36
33
37
34

The above is the detailed content of How to generate random integers in Java. For more information, please follow other related articles on the PHP Chinese website!