我如何使程序保持循环，直到用户输入了整数

Question

i am trying to modify my program so that even when the user has entered a string instead of the program crashing it should keep looping and asking for the user to enter the exam grade which needs to be an integer, only when the user has entered an integer should the program terminate. I am referring to the code in the do-while block

import java.util.InputMismatchException;
import java.util.Scanner;


public class CatchingException {

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int score;
    String choice;


    try {
    System.out.println("Enter your percentage mark: ");
    score = scan.nextInt();


    do {
        if(score <40) {
            System.out.println("You FAILED");
        }else if(score >=40 && score <50){
            System.out.println("Your grade: PASS MARK");
        }else if(score >=50 && score <60) {
            System.out.println("Your grade: 2:2");
        }else if (score >=60 && score <70) {
            System.out.println("Your grade: 2:1");
        }else {
            System.out.println("Your grade: 1:1");
        }

        System.out.println("Do you want to enter another grade: ");
        choice = scan.next();
        if(choice.equalsIgnoreCase("yes")) {
            System.out.println("Enter your percentage mark: ");
                score = scan.nextInt();
                System.err.println("Incorrect Input");
            }
    }while();

    }catch(InputMismatchException e) {
        System.err.println("Incorrect Input ");
    }

    System.out.println("program terminated");
    scan.close();

}

  }

Answer 1

Use a boolean variable to keep track of whether or not to keep looping. For example:

boolean loop = true;
do {
    // set loop to false when you want to end
} while(loop);

Answer 2

so you could do:

int score = null;
boolean isInt = false;

do {
    System.out.println("Enter your percentage mark:");

    try {
        score = scan.nextInt();
        isInt = true;
    } catch (InputMismatchException e) {
        //Not An Integer
        isInt = false;
    }
} while(false)

//Do you if statements here if it gets out of the while loop which means the user entered an int

Answer 3

Instead of assuming the number inputed is an int , you can input it as a String and loop until that string represents an int :

int intScore;
String score;
boolean gotInt = false;
while (!gotInt) {
    score = scan.next();
    try {
        intScore = Integer.valueOf(score);
        gotInt = true;
    } catch (NumberFormatException e) {
        // output some warning
    }
}

Answer 4

Did you consider using JOptionPane to get an input from the user? It is able to display a little window with a text field and a OK and Cancel button which would fit your needs perfectly.

Here is the documentation for JOptionPane#showInputDialog:

static String showInputDialog(Component parentComponent, Object message, String title, int messageType) 

Shows a dialog requesting input from the user parented to parentComponent with the dialog having the title title and message type messageType.