Java Algorithms How to - Generate a random number between multiple ranges

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Question

We would like to know how to generate a random number between multiple ranges.

Answer

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
// www. java2  s  .c o  m
public class Main {
  public static void main(String[] args) {
    RandomInRanges rir = new RandomInRanges(1, 10);
    rir.addRange(50, 60);
    System.out.println(rir.getRandom());
  }
}

class RandomInRanges {
  private final List<Integer> range = new ArrayList<>();

  RandomInRanges(int min, int max) {
    this.addRange(min, max);
  }

  final void addRange(int min, int max) {
    for (int i = min; i <= max; i++) {
      this.range.add(i);
    }
  }

  int getRandom() {
    return this.range.get(new Random().nextInt(this.range.size()));
  }

}

The code above generates the following result.

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