java random generator number in range code example

Example 1: how to get random number in java in range

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;
    }


    //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?

Example 2: how to generate random numbers in java within range

import java.util.Random;

Random rand = new Random();
int random_integer = rand.nextInt(upperbound-lowerbound) + lowerbound;