选择结构

选择结构

if单选结构

package com.xw.struct;

import java.util.Scanner;

public class IfD01 {
    public static void main(String[]args){
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入内容：");
        String s = scanner.nextLine();
        //equals:判断字符串是否相等
        if (s.equals("Hello")) {//如果s等于Hello输出s
            System.out.println(s);
        }
        /*else {//否则，没有else则不论s是否为Hello都会正常输出
        System.out.println("End");//输出End
        }*/
        scanner.close();
    }
}

if双选结构

package com.xw.struct;

import java.util.Scanner;

public class D02 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入分数");
        int s = scanner.nextInt();
        if (s>=60){
            System.out.println("及格");
        }else {
            System.out.println("不及格");
        }
        scanner.close();
    }
}

if多选结构

package com.xw.struct;

import java.util.Scanner;

public class D03 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入分数");
        int i = scanner.nextInt();
        if (i==0 && i<60){
            System.out.println("不及格");
        }else if (i>=60 && i<80){
            System.out.println("及格");
        }else if (i>=80  && i<100){
            System.out.println("优秀");
        }else if (i==100){
            System.out.println("恭喜满分");
        }else {
            System.out.println("成绩不合法");
        }
        scanner.close();

    }
}

嵌套的if.......eles都是合法的可以合理相互嵌套

switch多选结构

package com.xw.struct;

public class switchD01 {
    public static void main(String[] args) {
        //case穿透  //switch 匹配一个具体的值
        char grade ='B';
        switch (grade){
            case 'A':
                System.out.println("优秀");
                break;//可选
            case 'B':
                System.out.println("良好");
                break;//可选
            case 'C':
                System.out.println("挂科");
                break;//可选
            default:
                System.out.println("报错");
                break;//可选
        }
    }
}

package com.xw.struct;

public class switchD02 {
    public static void main(String[] args) {
        String name ="小王";
        //JDK7的特性，表达式结果可以
        // 是字符串
        //字符的本质还是数字

        //反编译
        switch (name){
            case "小李":
                System.out.println("小李");
                break;
            case "小王":
                System.out.println("小王");
                break;
            default:
                System.out.println("报错");
        }
    }
}