Subtle errors can happen in a try..catch

[Harry Kar]

That one i found it the hard way so  i put it here for others to take vision and possibly avoid

Assume you call that method from some other method in your project where you had setup a Scanner object for user's input
Method's logic is simple iterate on input's stream till you get a valid integer. In case of invalid user's input i.e. when nextInt() can’t convert input's string to an integer,
throw an InputMismatchException

What you get if you run the following method's code?  an infinite loop right? but why? ...

   public static int GetAnInteger() {
        while (true) {
            try {
                return sc.nextInt();
            }
            catch (InputMismatchException e) {               
                System.out.print("That's not an integer. Try again: ");
            } 
        } // while 
    } // GetAnInteger()

... because from API documentation

...When a scanner throws an InputMismatchException, the scanner will not pass the token that caused the exception, so that it may be retrieved or skipped via some other method...

So got you the trick?
nextInt() was leaving the invalid user input into the stream(I instead thought had to move on) and after catch's return in subsequent while's iterations nextInt() clearly read the same invalid character(and not the fresh one that should be provided by the user in the new iteration) throw his exception(ever leaving the same  invalid user input into stream)  and so on ad infinitum.

Ok found the culprit how to resolve?
It's trivially enough a  sc.next() between lines 6 and 7; that consume(gets rid) the invalid character and so now nextInt() can read correctly the fresh user's input

[Campbell Ritchie]

But there is no need ever to catch such en Exception. You use a loop to avoid that exception.
That is only an infinite loop if there is an error. It is actually a precondition on the reading; if the precondition is not fulfilled, the reading is allowed never to terminate.
input ∈ {String.valueOf(ℤ) | return sc.nextInt();

[Harry Kar]

Campbell Ritchie wrote:But there is no need ever to catch such en Exception. You use a loop to avoid that exception.
That is only an infinite loop if there is an error. It is actually a precondition on the reading; ...

Yeah i know all that . Put it exemplified and death clear as in my earlier post seems trivial but  if you put it into some thousands lines of code I can assure you it's not at all
The code  is not mine i only reviewed it and wanted share that possible subtle situation.

For who follow the discussion what CR refers in

But there is no need ever to catch such en Exception. You use a loop to avoid that exception.

mean that is more natural instead of the code in my earlier post write the following:  

public static int GetAnInteger() {
    while (!sc.hasNextInt()) { // repeat the following steps as long as hasNextInt() returns false 
                             // -indicating that the next value is not a valid integer-
                            //  The loop ends only when you give good data in the input stream

        sc.nextLine();              // discard the bad data
        System.out.print("That's not an integer. Try again: ");   // display an error message
   } // while

  return sc.nextInt(); // nextInt() is called only on good data ; the bad data are consumed in while

} // GetAnInteger()

[Campbell Ritchie]

Harry Kar wrote:. . .

public static int GetAnInteger() {
    while (!sc.hasNextInt()) { // repeat the following steps as long as hasNextInt() returns false 
                                           // -indicating that the next value is not a valid integer-
                                          //  The loop ends only when you give good data in the input stream

        sc.nextLine();              // discard the bad data
        System.out.print("That's not an integer. Try again: ");   // display an error message
   } // while

  return sc.nextInt(); // nextInt() is called only on good data ; the bad data are consumed in while

} // GetAnInteger()

Please check whether that code is correct; calling nextLine() may have unwanted side‑effects.

[Harry Kar]

Campbell Ritchie wrote:

Harry Kar wrote:. . .

public static int GetAnInteger() {
    while (!sc.hasNextInt()) { // repeat the following steps as long as hasNextInt() returns false 
                                           // -indicating that the next value is not a valid integer-
                                          //  The loop ends only when you give good data in the input stream

        sc.nextLine();              // discard the bad data
        System.out.print("That's not an integer. Try again: ");   // display an error message
   } // while

  return sc.nextInt(); // nextInt() is called only on good data ; the bad data are consumed in while

} // GetAnInteger()

Please check whether that code is correct; calling nextLine() may have unwanted side‑effects.

Please explain better

[Campbell Ritchie]

What if the user has entered a number, realised there was an error and tried to correct it?

The User of the input wrote:123x 124

. . . adding the x to 123 because it was incorrect.