Java How can I break a while loop under a switch statement?

Question

I have a homework to implement a simple testing application, below is my current code:

import java.util.*;

public class Test{

private static int typing;

public static void main(String argv[]){
    Scanner sc = new Scanner(System.in);
    System.out.println("Testing starts");
    while(sc.hasNextInt()){
        typing = sc.nextInt();
        switch(typing){
            case 0:
              break; //Here I want to break the while loop
            case 1:
              System.out.println("You choosed 1");
              break;
            case 2:
              System.out.println("You choosed 2");
              break;
            default:
              System.out.println("No such choice");
        }
    }
      System.out.println("Test is done");
    }
}

What I want to do now is that when 0 is pressed, it means that the user wants to quit the test, then I break the while loop and print Test is done, but it doesn't work like that, I know the reason might be that the "break" breaks the switch, how can I let it break the while loop instead?

betteroutthanin · Accepted Answer · 2014-04-02T21:38:20.983

180

You can label your while loop, and break the labeled loop, which should be like this:

loop: while(sc.hasNextInt()){
    typing = sc.nextInt();
    switch(typing){
        case 0:
          break loop; 
        case 1:
          System.out.println("You choosed 1");
          break;
        case 2:
          System.out.println("You choosed 2");
          break;
        default:
          System.out.println("No such choice");
    }
}

And the label can be any word you want, for example "loop1".

edited Apr 02 '14 at 21:38

answered Apr 02 '14 at 21:26

betteroutthanin

7,148
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41

"loop" is a poor/boring choice of label. Funnier choices include "up", "out", "stuff", "theBank" and "dance". – jakber Apr 14 '15 at 13:23
6

Jokes aside, giving the loop a slightly more informative label (in your case, perhaps `scanner`), allows the breaks to look like `break scanner` (stop scanner). – noamtm Jun 21 '16 at 06:15
@noamtm that wasn't obvious, so thanks for pointing that out. – John R Perry Apr 23 '18 at 11:41

score 14 · Answer 2 · answered Apr 02 '14 at 21:25

You need a boolean variable e.g. shouldBreak.

    boolean shouldBreak = false;
    switch(typing){
        case 0:
          shouldBreak = true;
          break; //Here I want to break the while loop
        case 1:
          System.out.println("You choosed 1");
          break;
        case 2:
          System.out.println("You choosed 2");
          break;
        default:
          System.out.println("No such choice");
    }
    if (shouldBreak) break;

score 5 · Answer 3 · edited Jul 24 '17 at 08:05

Put the while inside a function and when you press 0 instead of break just return. For example :

    import java.util.*;

public class Test{

private static int typing;

public static void main(String argv[]){
    Scanner sc = new Scanner(System.in);
    func(sc);
      System.out.println("Test is done");
    }
}

public static void func(Scanner sc) {


    System.out.println("Testing starts");
    while(sc.hasNextInt()){
        typing = sc.nextInt();
        switch(typing){
            case 0:
              return; //Here I want to break the while loop
            case 1:
              System.out.println("You choosed 1");
              break;
            case 2:
              System.out.println("You choosed 2");
              break;
            default:
              System.out.println("No such choice");
        }
    }
}

}

score 1 · Answer 4 · answered Dec 09 '17 at 17:35

How to terminate inner menu ?

Example Code :

import java.util.Scanner;

public class Example {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in); //used to get input
        int option1, option2 = 0;
        boolean loop_terminate = true; //flag used to terminate inner while loop

        //Main Menu
        while (true) {
            //Main Menu options
            System.out.println("1.Option 1");
            System.out.println("2.Option 2");
            System.out.println("3.Option 3");
            System.out.println("4.Option 4");
            System.out.println("5.Exit main menu");

            System.out.print("Please enter your choice : ");
            option1 = input.nextInt();

            switch (option1) {

                case 1:
                       //do something here    
                    break;
                case 2:
                       //do something here 
                    break;
                case 3:

                    while (loop_terminate) {
                        //Inner menu options
                        System.out.println("1.Inner Menu option 1");
                        System.out.println("2.Inner Menu option 2");
                        System.out.println("3.Inner Menu option 3");
                        System.out.println("4.Return to Main Menu");

                        System.out.print("Please enter your choice : ");
                        option2 = input.nextInt();
                        switch (option2) {

                            case 1:
                                break;
                            case 2:
                                break;
                            case 3:
                                break;
                            case 4:
                                loop_terminate = false; //this will terminate inner menu
                                break;
                            default:
                                System.out.println("Invalid option");
                                break;
                        }
                    }
                    break; //never forget to add this break statement
                case 4:
                      break;
                case 5:
                    return; //terminate outer menu

                default:
                    System.out.println("Invalid option");
            }
        }

    } 
}

Java How can I break a while loop under a switch statement?

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