順序控制

按著順序一個一個執行

選擇結構

1. if單選結構

   package com.zhaowei.example.struct;
   ​
   import java.util.Scanner;
   ​
   //if  單選結構
   public class Demo1 {
      public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        System.out.println("請輸入內容：");
        String str=scanner.nextLine();
        //equals判斷字串是否相等
        if(str.equals("Hello")){
          System.out.println(str);
        }
        System.out.println("End");
        scanner.close();
      }
   }
   ​
    
   

2. if 雙選擇結構

   package com.zhaowei.example.struct;
   ​
   import java.util.Scanner;
   ​
   public class Demo2 {
      public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        System.out.println("請輸入成績：");
        int score=scanner.nextInt();
        if(score>60){
          System.out.println("及格");
        }
        else{
          System.out.println("不及格");
        }
        scanner.close();
      }
   }
   ​
    
   

3. if多選擇結構

   package com.zhaowei.example.struct;
   ​
   import java.util.Scanner;
   ​
   public class Demo3 {
      public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        System.out.println("請輸入成績：");
        int score=scanner.nextInt();
        if(score==100){
          System.out.println("恭喜滿分");
        }
        else if(score<100 &&score>=90){
          System.out.println("A級");
        }
        else if(score<90 &&score>=80){
          System.out.println("B級");
        }else if(score<80&&score>=70){
          System.out.println("C級");
        }
        else if(score<70 &&score>=60){
          System.out.println("D級");
        }
        else if(score<60){
          System.out.println("不及格");
        }
        else{
          System.out.println("成績不合法");
        }
      }
   }
   ​
    
   

   4. 巢狀的if結構

      package com.zhaowei.example.struct;
      ​
      import java.util.Scanner;
      ​
      public class Demo4 {
         public static void main(String[] args) {
           Scanner scanner=new  Scanner(System.in);
      ​
           int guess=(int)(Math.random()*100+1);
           System.out.println("請輸入一個數："+guess);
           while(true){
             int num=scanner.nextInt();
             if(num<guess){
               System.out.println("小了");
      ​
             }
             else  if(num>guess){
               System.out.println("大了");
             }
             else{
               System.out.println("猜對了");
             }
           }
      ​
         }
      }
      ​

   5. switch多選擇結構

      package com.zhaowei.example.struct;
      ​
      public class Demo5 {
         public static void main(String[] args) {
           //
           char grade='C';
           switch (grade){
             case 'A':
               System.out.println("優秀");
               break;
             case 'B':
               System.out.println("良好");
               break;
             case 'C':
               System.out.println("及格");
               break;
             case  'E':
               System.out.println("不及格");
             default:
               System.out.println("成績等級不知道");
               break;
           }
         }
      }
      //jdk7以後可以用表示字串！！！
      ​
      package com.zhaowei.example.struct;
      ​
      public class Demo6 {
         public static void main(String[] args) {
           String name="zhao";
           switch (name){
             case "zhao":
               System.out.println("zhao");
               break;
             case "zw":
               System.out.println("zw");
               break;
             default:
               System.out.println("不知道");
               break;
           }
         }
      }