Java学习----反复做某件事情

 for循环:

public class TestFor{
    public static void main(String[] args){
       for(int x = 1; x < 3; x++) {
          System.out.println(x);
       }
    }
}

计算1+2+3...+100的值

public class TestFor{
    public static void main(String[] args){
       int sum = 0;

       // 计算1+2+.....+100的值
       for(int x = 1; x <= 100; x++) {
           sum = sum + x; // sum += x
       }
       System.out.println(sum);
    }
}

while循环：

public class TestWhile{
    public static void main(String[] args){
       int x = 1;
       /*
       while (x <= 3) {
          System.out.println(x);
          if (x == 1) {
             continue;//死循环1
          }
          x++;
          if (x == 2) {
             break;//终止循环
          }
       } */

       do {
          System.out.println(x);
          x++;
       }while(x <= 3);
       System.out.println("循环结束");
    }
}