java-for循环

package com.lemon.operator;

public class for_demo {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        // for循环,格式
        for(int i = 1;i<=4;i++) {
            System.out.println("******");
        }
        System.out.println("循环结束");
    }
//      test
        int[] arr = {100,200,300,400,500};
        for(int i = 0;i < arr.length;i++) {
            System.out.println(arr[i]);
        }

    
}

//结果
******
******
******
******
循环结束
100
200
300
400
500

增强for循环

package com.lemon.operator;

public class for_demo {

    public static void main(String[] args) {
        int[] arr = {100,200,300,400,500};
//      增强for循环,只能循环数组和集合
//      缺点，没有索引，只能从头遍历到尾
//      优点：代码少
//      arr数组的元素是int类型，所以是int
        for(int element:arr) {
            System.out.println(element);
        }   
        System.out.println("==============");

//      arr2数组的元素是string类型，所以for循环里是String
        String[] arr2 = {"ab","11","00"};
        for(String str :arr2) {
            System.out.println(str);
        }
            
    }

}

//结果
100
200
300
400
500
==============
ab
11
00

求和思想

package com.lemon.operator;

public class ForDemo3 {

    public static void main(String[] args) {
        //求和思想
        //求1-10的和
        int sum = 0;
        for(int i =1 ;i<= 10;i++) {
            sum += i;
            System.out.println(sum);
        }
        System.out.println(sum);
    }
}
//结果
55

while循环

package com.lemon.operator;

public class whileDemo {

    public static void main(String[] args) {
        // while 输出 1-5
        int i = 1;
        while(i < 5) {
            System.out.println(i);
            i++;
        }

    }
}

//结果
1
2
3
4