Java while循环和分支

叁歲伎倆 2023-10-12 20:27 2阅读 0赞

#### while循环和分支 ####

*   *  while 循环
     *  while 循环案例
     *  do-while
     *  if分支
     *  switch
     *  switch 注意事项
     *  for 循环

### while 循环 ###

package com.ithema.spedkey;
    
    public class demo6241 {
        
        public static void main(String[] args) {
        
            // 理解while
            int i = 0;
            while (i < 5){
        
                System.out.println("Hello word");
                i++;
            }
        }
    }

![在这里插入图片描述][f68c03a01e584cf48a20a944b1c0ac8a.png]  
![在这里插入图片描述][5db5121eaa384f648eb7ebbb7a3644ee.png]

### while 循环案例 ###

![在这里插入图片描述][ca6f939f4f9b4f779bc781b78dbd0e66.png]

package com.ithema.loop;
    
    public class test {
        
        public static void main(String[] args) {
        
            // 使用while
            double peak = 8848860;
            double paper = 0.1;
    
            int i = 0;
            while (paper < peak){
        
    
                paper *= 2;
                i++;
            }
            System.out.println("纸张折叠了"+i+"次");
            System.out.println(paper);
        }
    }

### do-while ###

![在这里插入图片描述][f677530a5fdd41d6b919fafe1430aee9.png]

package com.ithema.loop;
    
    public class test {
        
        public static void main(String[] args) {
        
            // 使用do-while
           int i = 0;
           do{
        
               System.out.println("Hello world");
               i++;
           } while (i < 3);
        }
    }

![在这里插入图片描述][71b08657576048f99fc52d9ce3f0a20c.png]

先执行 后判断

package com.ithema.loop;
    
    public class test {
        
        public static void main(String[] args) {
        
            // 使用do-while
    
           int i = 0;
           do{
        
               System.out.println("Hello world");
               i++;
           } while (i < 3);
    
            // 先执行 后判断
           do{
        
               System.out.println("heheheheheheh");
           } while(false);
        }
    }

![在这里插入图片描述][6304148cc5f442e399f8a9151cf019fc.png]

package com.ithema.loop;
    
    public class test {
        
        public static void main(String[] args) {
        
            for (int i = 0; i < 3; i++) {
        
                System.out.println("hello");
            }
            // 不能识别i
        }
    }

### if分支 ###

![在这里插入图片描述][65eadfb805d74dcb9c161e2e0a98ddf8.png]

package com.ithema.loop;
    
    public class test {
        
        public static void main(String[] args) {
        
            double t = 38.9;
            if (t > 37){
        
                System.out.println("大于37");
            }
    
            double money = 90;
            if (money > 99){
        
                System.out.println("够了");
            }
            else{
        
                System.out.println("不够");
            }
    
            int score = 40;
            if (score >= 90){
        
                System.out.println("优秀");
            }
            else if (score >= 80){
        
                System.out.println("良好");
            }
            else if (score >= 60){
        
                System.out.println("及格");
            }
            else{
        
                System.out.println("不及格");
            }
    
            // 一种情况
            int a = 17;
            if (a < 30) System.out.println("haha");
    
        }
    }

输出

大于37
    不够
    不及格
    haha

### switch ###

![在这里插入图片描述][234e64d4f63c4da3940b77352bcc9f00.png]

package com.ithema.loop;
    
    public class demo241 {
        
        public static void main(String[] args) {
        
            String week = "周三";
            switch (week) {
        
                case "周一":
                    System.out.println("周一啊");
                    break;
                case "周二":
                    System.out.println("周二啊");
                    break;
                default:
                    System.out.println("咋回事儿？");
            }
        }
    }

输出

咋回事儿？

### switch 注意事项 ###

![在这里插入图片描述][e365536ae11245ca9497d2fa9b9b5903.png]

package com.ithema.loop;
    
    public class demo241 {
        
        public static void main(String[] args) {
        
            // 支持：byte、short、int、char、string等
            // 不支持double、float、long
            int a = 10;
            switch (a) {
        
                case 10:
                    System.out.println(10);
    
            }
            // case 给出的值不允许重复，只能是字面量，不能是变量
            // 不要忘记写break，否则会出现穿透
    
            
        }
    }

![在这里插入图片描述][f4b1acb6a65a4963b320148d8c1699c0.png]

package com.ithema.loop;
    
    public class demo241 {
        
        public static void main(String[] args) {
        
            // 周一打游戏
            // 周二打游戏
            // 周三打游戏
            // 周四做饭
            // 周五做饭
            // 周六什么
            // 周七啥
    
            String week = "周三";
            switch (week){
        
                case "周一":
                case "周二":
                case "周三":
                    System.out.println("打游戏");
                    break;
                case "周四":
                case "周五":
                    System.out.println("做饭");
                    break;
                case "周六":
                    System.out.println("什么");
                    break;
                case "周天":
                    System.out.println("啥");
                    break;
                default:
                    System.out.println("none");
            }
        }
    }

### for 循环 ###

快捷键：`fori + tab`

![在这里插入图片描述][7f0d27000fb348909c3f65d1e21767df.png]

package com.ithema.loop;
    
    public class demo241 {
        
        public static void main(String[] args) {
        
            for (int i = 0; i < 5; i++) {
        
                System.out.println("hello world"+i);
            }
    
            System.out.println("-------------------------");
    
            for (int i = 2; i < 5; i++) {
        
                System.out.println("hello world"+i);
            }
    
            System.out.println("-------------------------");
    
            for (int i = 1; i < 15; i+=2) {
        
                System.out.println("hello world"+i);
            }
    
            System.out.println("-------------------------");
    
            for (int i = 1; i < 10; i+=2) {
        
                System.out.println("hello world"+i);
                i-=1;
            }
    
        }
    }

输出

hello world0
    hello world1
    hello world2
    hello world3
    hello world4
    -------------------------
    hello world2
    hello world3
    hello world4
    -------------------------
    hello world1
    hello world3
    hello world5
    hello world7
    hello world9
    hello world11
    hello world13
    -------------------------
    hello world1
    hello world2
    hello world3
    hello world4
    hello world5
    hello world6
    hello world7
    hello world8
    hello world9

> 前五整数求和

package com.ithema.loop;
    
    public class demo241 {
        
        public static void main(String[] args) {
        
            int count = 0;
            for (int i = 1; i <= 5 ; i++) {
        
                count += i;
            }
            System.out.println(count);
        }
    }

[f68c03a01e584cf48a20a944b1c0ac8a.png]: https://img-blog.csdnimg.cn/f68c03a01e584cf48a20a944b1c0ac8a.png
[5db5121eaa384f648eb7ebbb7a3644ee.png]: https://img-blog.csdnimg.cn/5db5121eaa384f648eb7ebbb7a3644ee.png
[ca6f939f4f9b4f779bc781b78dbd0e66.png]: https://img-blog.csdnimg.cn/ca6f939f4f9b4f779bc781b78dbd0e66.png
[f677530a5fdd41d6b919fafe1430aee9.png]: https://img-blog.csdnimg.cn/f677530a5fdd41d6b919fafe1430aee9.png
[71b08657576048f99fc52d9ce3f0a20c.png]: https://img-blog.csdnimg.cn/71b08657576048f99fc52d9ce3f0a20c.png
[6304148cc5f442e399f8a9151cf019fc.png]: https://img-blog.csdnimg.cn/6304148cc5f442e399f8a9151cf019fc.png
[65eadfb805d74dcb9c161e2e0a98ddf8.png]: https://img-blog.csdnimg.cn/65eadfb805d74dcb9c161e2e0a98ddf8.png
[234e64d4f63c4da3940b77352bcc9f00.png]: https://img-blog.csdnimg.cn/234e64d4f63c4da3940b77352bcc9f00.png
[e365536ae11245ca9497d2fa9b9b5903.png]: https://img-blog.csdnimg.cn/e365536ae11245ca9497d2fa9b9b5903.png
[f4b1acb6a65a4963b320148d8c1699c0.png]: https://img-blog.csdnimg.cn/f4b1acb6a65a4963b320148d8c1699c0.png
[7f0d27000fb348909c3f65d1e21767df.png]: https://img-blog.csdnimg.cn/7f0d27000fb348909c3f65d1e21767df.png