1.for循环

public class ForDemo1 {
    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            System.out.println("HelloWorld");
        }
        System.out.println("--------------------------------------------");
        for (int i = 1; i <=10 ; i++) {
            System.out.println("HelloWorld1");
        }
        System.out.println("--------------------------------------------");
        for (int i = 1; i <=10 ; i+=2) {
            System.out.println("HelloWorld2");
        }
    }
}

public class ForDemo2 {
    public static void main(String[] args) {
        // 目标：打印输出1-100的数据，求1-100的和
        for (int i = 1; i < 101; i++) {
            System.out.println(i);
        }
        int sum = 0;
        System.out.println("---------------------------------------");
        for (int i = 1; i <= 100 ; i++) {
            sum += i;
        }
        System.out.println(sum);
        System.out.println("----------------------------------------");
        /**
         * 计算1-100之间的奇数和
         */
        int sum1 = 0;
        for (int i = 0; i < 100; i++) {
            if (i % 2 == 1){
                sum1 += i;
            }
        }
        System.out.println(sum1);
    }
}

 2.while循环

// while循环
public class WhileDemo3 {
    public static void main(String[] args) {
        int i = 0;
        while (i < 5){
            System.out.println("HelloWorld");
            i++;
        }
    }
}

 3.do-while循环

public class DoWhileDemo5 {
    public static void main(String[] args) {
        int i = 0;
        do {
            System.out.println("HelloWorld");
        }while (i < 0);
        // while循环中的变量可以在while外部使用
        System.out.println(i);

        // 而for中定义的变量只能在for循环中使用，不能在外部使用
        for (int j = 0;j < 4;j++){
            System.out.println(j);
        }
        // System.out.println(j);  报错
    }
}

 4.死循环

public class EndLessLoopDemo6 {
    public static void main(String[] args) {
        // 死循环的三种写法
        /*for (; ;) {
            System.out.println("HelloWorld");
        }*/
      /*  while (true){
            System.out.println("HelloWorld1");
        }*/
  /*      do {
            System.out.println("HelloWorld");
        }while (true);*/
    }
}

5.嵌套循环 

public class LoopNestedDemo7 {
    public static void main(String[] args) {
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 5; j++) {
                System.out.println("抽死你");
            }
            System.out.println("----------------------------------");
        }
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 4; j++) {
                System.out.print("*");
            }
            System.out.println();   // 换行
        }
    }
}

6.跳转关键字 

public class BreakAndContinueDemo8 {
    public static void main(String[] args) {
        // 目标：掌握break和continue的执行
        // 1.break:跳出并结束当前所在循环
        for (int i = 1; i <= 5; i++) {
            System.out.println("。。。");
            if (i == 3) {
                break;
            }
        }
        for (int i = 0; i < 5; i++) {
            System.out.println("。。。");
            if (i == 2) {
                break;
            }
        }
        for (int i = 0; i < 5; i++) {
            if (i == 3) {
                break;
            }
            System.out.println("。。。");
        }
        // 2.continue:提出本次循环，执行下一次循环
        // 第一天干活，第二天干活，第三天休息，第四天干活
        for (int i = 1; i <= 4; i++) {
            if (i == 3){
                System.out.println("第"+i+"天休息");
                continue;
            }else {
                System.out.println("第"+i+"天干活");
            }
        }
    }
}