生成随机数

[0,20)

[10,20)

[10,50]

import javax.swing.JOptionPane;
import java.util.*;
class Main {
  public static void main(String[] args){
    int number = (int)(Math.random() * 100) % 20;
    System.out.println(number);
    
    number = 10 + (int)(Math.random() * 100) % 10;
    System.out.println(number);

    number = 10 + (int)(Math.random() * 100) % 41;
    System.out.println(number);
  }

}