为什么这段代码不起作用（基本）

Question

它不允许我输入我的选择是否要进入另一个年级，它应该允许我选择是或否，如果我输入是，它应该允许我进入另一个年级，除了它只是拒绝接受用户输入？

import java.util.Scanner;

public class ExaminationGrades {

    public static void main(String[] args) {
        Scanner scan = new Scanner (System.in);
        double grade;
        String ch;

        do {
            System.out.println("Enter your grade: ");
            grade = scan.nextDouble();

            if (grade <40) {
                System.out.println("you failed");
            } else if (grade >=40 && grade <50) {
                System.out.println("Pass");
            } else if (grade >=50 && grade <60) {
                System.out.println("2:2");
            } else if (grade >=60 && grade <70){
                System.out.println("2:1");
            } else if (grade >=70 && grade <=100){
                System.out.println("1:1");
            } else
                System.out.println("invalid entry");

            System.out.println("Would you like to enter another?");
            ch = scan.nextLine();

        } while(ch =="no");

        scan.close();
    }

}

Answer 1

更改

while(ch =="no");

到

while(ch.equals("yes"))

修改

public static void main(String[] args) {
    Scanner scan = new Scanner (System.in);
    double grade;
    String ch;

    do {
        System.out.println("Enter your grade: ");
        grade = scan.nextDouble();
        scan.nextLine(); //Consume the newline character generated by hitting enter

        if (grade <40) {
            System.out.println("you failed");
        }else if (grade >=40 && grade <50) {
            System.out.println("Pass");
        }else if (grade >=50 && grade <60) {
            System.out.println("2:2");
        }else if (grade >=60 && grade <70){
            System.out.println("2:1");
        }else if (grade >=70 && grade <=100){
            System.out.println("1:1");
        }else
            System.out.println("invalid entry");

        System.out.println("Would you like to enter another?");
        ch = scan.nextLine();

    }while(ch.equals("yes")); //Correctly compare strings

    scan.close();
}