Exception in thread "main" java.util.InputMismatchException

[W Wilson]

So I'm having a bit of an issue, I'm quite stuck.

So, I have this program. The first method gets the input of an integer from the user and then passes it to another method which checks it to be in a range. That works fine. The problem is that if they enter something other than an int such as a double or a string, it causes an exception and the program crashes. Now, I need to handle this, as simple of just making it say what the issue was and then calling the method that requires them to enter the integer again, but I just can't remember how to handle this exception and unfortunately, my searches on google, here, and through my textbook have not been very helpful.

Please enter your age: notint
Exception in thread "main" java.util.InputMismatchException
	at java.util.Scanner.throwFor(Scanner.java:864)
	at java.util.Scanner.next(Scanner.java:1485)
	at java.util.Scanner.nextInt(Scanner.java:2117)
	at java.util.Scanner.nextInt(Scanner.java:2076)
	at Ch2ProgLabWilson.getAge(Ch2ProgLabWilson.java:21)
	at Ch2ProgLabWilson.main(Ch2ProgLabWilson.java:14)

public static int getAge()
     {
      Scanner keyboard = new Scanner(System.in);
      System.out.print("Please enter your age: ");
      int a = keyboard.nextInt();
      verifyAge(a);
      return a;
     }
     
     // 
     public static boolean verifyAge (int a)
         {
            if (a >= 0 && a <= 122)
            {
               System.out.println("The age you entered, " + a + ", is valid.");
               return true;
            }
            else
            {
               System.out.println("The age must be from 0 to 122, cannot be negative, and has to be an integer.");
               getAge();
               return false;
            }   
         }

[Steve Kedzie]

Maybe this will help point you in the right direction:

http://docs.oracle.com/javase/tutorial/essential/exceptions/

You may also want to consult the API documentation. When you click on say, java.lang, you will also find a list of exception classes.

Steve

[W Wilson]

Right, so after looking into it, I get to a point where I can compile, except my exception handling isn't seeming to be working. It doesn't seem to be catching the exception and just returning it to JVM.

Exception in thread "main" java.util.InputMismatchException
	at java.util.Scanner.throwFor(Scanner.java:864)
	at java.util.Scanner.next(Scanner.java:1485)
	at java.util.Scanner.nextInt(Scanner.java:2117)
	at java.util.Scanner.nextInt(Scanner.java:2076)
	at Ch2ProgLabWilson.getAge(Ch2ProgLabWilson.java:22)
	at Ch2ProgLabWilson.main(Ch2ProgLabWilson.java:15)

public static int getAge()
     {
      Scanner keyboard = new Scanner(System.in);
      System.out.print("Please enter your age: ");
      int a = keyboard.nextInt();
      verifyAge(a);
      
      
      try
         {
            System.out.print("Please enter your age: ");
            a = keyboard.nextInt();
            verifyAge(a);
            return a;
         }   
      catch (InputMismatchException e)
         {
            System.out.println("You may only enter integers as an age. Try again.");
            getAge();
         }
         
       return a;
       }

[Campbell Ritchie]

Welcome to the Ranch

You are requesting the same input twice. Once before the try once inside it.

Never try handling an InputMismatchException (IME). The right way (in my opinion) to use a Scanner pointing to System.in is inside a utility class. You would have to write your own utility class. You can create a method something like

public static int getIntFromKeyboard(Sring message)
{
   System.out.print(message);
   while (myScanner.hasNextInt())
   {
      myScanner.next();
      System.err.print("Incorrect format for number: please try again: ");
   }
   return myScanner.nextInt();
}

Now, a long time ago, Rob Spoor taught me that you can always avoid an IME when you use the keyboard by getting the program to ask for a new input and showed me something very similar to the above. A few more suggestions can be found in my old posts if you search them for Scanner nextInt hasNextInt and utility class.

If you create yourself a utility class, you can overload that method to return a value in a certain range only. Use something like while (i < min || i > max) …, and remember you will get a nice infinite loop if you pass max less than min

If you do that, you can be certain to avoid the IME for int inputs, but remember that technique does not work at all well if you are reading from a file. It would need locking if used in a multithreaded environment.