选择结构

选择结构

if单选择结构

package ifDemo;

import java.util.Scanner;

public class ifDemo1 {
    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")) {
            System.out.println(s);
        }
        System.out.println("End");
        scanner.close();
    }
}

if双选择结构

package struct;

import java.util.Scanner;

public class ifDemo2 {
    public static void main(String[] args) {
        //考试分数大于等于60就是及格，小于60就不及格
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩：");
        int score = scanner.nextInt();
        if (score >= 60) {
            System.out.println("及格");
        } else {
            System.out.println("不及格");
        }
        scanner.close();
    }
}

if多选择结构

package struct;

import java.util.Scanner;

public class ifDemo3 {
    public static void main(String[] args) {
        //考试分数大于60就是及格，小于60分就是不及格
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩（数值）：");
        int score = scanner.nextInt();
        if (score == 100) {
            System.out.println("恭喜满分");
        } else if (score < 100 && score >= 90) {
            System.out.println("A级");
        } else if (score < 90 && score >= 80) {
            System.out.println("B级");
        } else if (score < 80 && score >= 70) {
            System.out.println("C级");
        } else if (score < 70 && score >= 60) {
            System.out.println("D级");
        } else if (score < 60 && score >= 0) {
            System.out.println("不及格");
        } else {
            System.out.println("成绩不合法");
        }
        scanner.close();
    }
}

嵌套的if结构

switch多选择结构

package struct;

public class SwitchDemo1 {
    public static void main(String[] args) {
        //case穿透  //switch匹配一个具体的值
        char grade = 'C';
        switch (grade) {
            case 'A':
                System.out.println("优秀");
                break;
            case 'B':
                System.out.println("良好");
                break;
            case 'C':
                System.out.println("及格");
                break;
            case 'D':
                System.out.println("再接再厉");
                break;
            case 'E':
                System.out.println("挂科");
                break;
            default:
                System.out.println("未知等级");
        }
    }
}