不能使String等于方法，并且不能将Strings转换为Numbers。

Question

It is a Java beginner question. The program is not complicated, it just asks the user input grade and then finish it when the user input "y" , and then calculate max, min,average, and total.

My trouble is that I can't stop the loop when I type y. Thank you so much, if anyone can help me out. I have tried many approaches to figure that.

    do
       { 
        System.out.println("please go on");
        input = keyboard.next();                    
        grade = Integer.parseInt(input);
        InputTimes++;
        if (grade>Maxgrade)
        {   
            Maxgrade = grade;       
         }

        if(Mingrade>grade)
        {
            Mingrade= grade;            
        }

        if (input.equals("y"))
        {   
            GameOver = true;
            System.out.println("yyyyyyy");
            break;
        }   
        else 
        {
            GameOver = false;
            System.out.println("nnnnnn");   
        }   
        totalgradeNoF = grade+totalgradeNoF;

    }while(GameOver==false);

Answer 1

Scanner keyboard = new Scanner(System.in);
int Maxgrade = 0, Mingrade = 0, InputTimes = 0, grade = 0, totalgradeNoF = 0;
boolean GameOver = false;
String input = "";
do {
    System.out.println("Please go on : ('y' to stop)");
    input = keyboard.nextLine();
    if (input.equals("y")) {
        GameOver = true;
    } else {
        grade = Integer.parseInt(input);
        InputTimes++;

        if (grade > Maxgrade) {
             Maxgrade = grade;
        }
        if (Mingrade > grade) {
             Mingrade = grade;
        }

        totalgradeNoF = grade + totalgradeNoF;
   }
} while (!GameOver);

Some things to change :

• You need to check the "y" BEFORE and if it is not a "y" so you can cast to int
• You don"t need to use break so
• You may use !GameoOver instead of GameOver==false
• Don't need to set Gameover=false at each iteration, just at the initialisation

Answer 2

当您输入“ y”时，NumberFormatException即将到来，因此您需要处理此异常，然后在键入“ y”后可以退出循环。

Answer 3

Use for Scanner methods nextInt() and nextLine() for reading input.

EX:-

Scanner scan = new Scanner(System.in);

then we can use scan.nextInt() for get int

and we can use scan.nextLine() for get Strings

https://www.tutorialspoint.com/java/util/scanner_next.htm
this link may be help for you.

sorry for my english.