选择结构

选择结构

1. 单if选择结构

import java.util.Scanner;

//单if选择结构
public class IfDemo01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();

        if (str.equals("hello")){
            System.out.println("执行了if里面");
        }

        System.out.println("if外面");

        scanner.close();
    }
}

2. if双分支结构

public class IfDemo02 {
    //if双选择结构
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();

        if (str.equals("a")){
            System.out.println("成功");
        }else {
            System.out.println("失败");
        }

        scanner.close();
    }
}

3. if多选择结构

public class IfDemo03 {
    //if多选择结构
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入你的成绩：");
        int score = scanner.nextInt();

        /**
         * 语句至多有一个else语句，并且在所有else if之后
         * 一旦else if为true，其他else if和else都将跳过
         */

        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("不合格");
        }else {
            System.out.println("成绩不合法！");
        }

        scanner.close();
    }
}

4. switch匹配一个具体的值

public class SwitchDemo01 {

    static String grade = "A";

    public static void main(String[] args) {
        /**
         *  switch匹配一个具体的值
         */

        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("不及格");
                break;
            default:
                System.out.println("输入不合法！");
                break;
        }
    }

}

5. JDK1.7以后，switch支持string

public class SwitchDemo02 {
    //JDK1.7以后，switch支持string
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();

        switch (str) {
            case "中国":
                System.out.println("加油！");
                break;
            case "武汉":
                System.out.println("必胜！");
                break;
            default:
                System.out.println("输入错误");
                break;
        }
    }
}