If 选择结构

package zaiyang.struct;

import java.util.Scanner;

public class ifDemo01 {
    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("不对，请重新输入！");
        scanner.close();
    }
}

package zaiyang.struct;

import java.util.Scanner;

public class IfDemo02 {
    public static void main(String[] args) {
        //考试分数大于60分就是及格，小于60分就不及格。

        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩：");
        Double score = scanner.nextDouble();

        if (score>60){
            System.out.println("及格");
        }else{
            System.out.println("不及格");
        }


        scanner.close();
    }
}

package zaiyang.struct;

import java.util.Scanner;

public class IfDemo03 {
    public static void main(String[] args) {
        //考试分数大于60分就是及格，小于60分就不及格。

        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩：");
        Double score = scanner.nextDouble();

        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();
}
}