Why does next() method stop infinite loop?

Question

Let's say I have this code:

 public static void main(String[] args) 
 {  
      Scanner key01 = new Scanner(System.in);
    int input;

    System.out.println("Please enter a int.");
      while (key01.hasNext()) 
      {
       if(key01.hasNextInt())
        {
         input = key01.nextInt();
         System.out.println("Thanks for input!");
        }
       else
       {
        System.out.println("You must enter an Int");
        key01.next(); //Why does this statement prevent an infinite loop?  
        //That statement prevents 
        //the program from constantly printing "you must enter an int"
       }
    }
}

How does key01.next() prevent the console from constantly printing out the error message?

Answer 1

Your loop is on the condition Scanner.hasNext() ; but your if checks if it specifically has an int . Without the call to next() in the else , when the pending token is not an int nothing would consume it; thus causing an infinite loop. Your key01.next() simply consumes the pending token.

Answer 2

If you implement an infinite loop ( while(true) ), Scanner.next() will throw an NoSuchElementException, when your scanner does not have additional elements. This exception would prevent an endless loop.

Elliot's answer explainswhy next() consumes the pending token; and then if you don't have additional tokens in your (not infinite, because it has a condition that gets false) loop. But this isn't what you've asked in your inline comments...