Cannot Figure out how to catch InputMismatchExcept

问题:

So here is my current code for catching an InputMismatchException error

int weapon = 0
   boolean selection = true;
   while(selection) {
    try {
      System.out.println("Pick number 1, 2, or 3.");
      weapon = scan.nextInt(); 
      selection = false;
    } catch(InputMismatchException e) {
        System.out.println("Choose 1,2,3");
        weapon = scan.nextInt();
      }
   }

I'm trying to make sure that an int is entered and not anything else. Scanner class as already been implemented and 'scan' will act as it for me.

Thanks for any efforts to help!

回答1:

Try this:

int weapon = 0;
   do{
       System.out.println("Pick number 1, 2, or 3.");
       if(scan.hasNextInt()){
           weapon = scan.nextInt();
           break;
       }else{
           System.out.println("Enter an integer only");
           scan.nextLine();
       }
   }while(true);

This will make sure it is an integer and it will keep asking until it gets it.

回答2:

In the first place, you already have a loop with which to prompt for and scan the desired int. You do not need to duplicate that behavior in your exception handler. What you do need to do, however, is discard the mismatching token from the scanner in order to allow a new one to be scanned.

As a secondary matter, your selection variable appears to be redundant.

It looks like this might do what you're after:

int weapon = 0
while(weapon < 1 || weapon > 3) {
    try {
        System.out.println("Pick number 1, 2, or 3.");
        weapon = scan.nextInt(); 
    } catch(InputMismatchException e) {
        //discard the mismatching token
        scan.next();
    }
}