Thread: Loop using Scanner with try/catch

Hello all

I haven't used Java in years been pursuing a Black Belt in a traditional martial art and received an injury and have had a 'lot' of free time recently so I decided to play around with some Java programming again and it's changed a lot.

When I last used Java receiving user input wasn't handled with a scanner and there were no try/catch options. So I have used these things trying to get user input, and make sure a user enters a number, if not create a loop to go back and ask the user to enter again.

Now, if the user enters a number all good, but, I just can't figure why the code goes into an infinite loop if the user enters anything else. It doesn't stop and ask the user to enter a number again?!? It just repeats the catch message. Any help would be greatly appreciated.

And I used the following code: excuse the formatting I am coding in notepad and its not exactly the most readable:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
import java.util.Scanner;
 
//needed for the InputMismatchError
import java.util.* ;
 
public class First {
 
    public static void main(String args[]) {
        System.out.println(" You have just run HelloWorld !");
	//BufferedReader br = new BufferedReader();
	Scanner numberScan=new Scanner(System.in);
 
	System.out.println("\nEnter a number");
 
	//create system to ask for user input if entry is wrong
	boolean entryWrong = true;
 
	//get user input
	//this is totally weird;
	int userInt;
 
	//try/catch pairing exception error if user doesn't enter a number,ie int
	//in this case
 
	//while(userEntry==true){
	while(true){
	try{
		userInt = numberScan.nextInt();
		System.out.println("You Entered a number: "+ userInt);	
		break;
		//userEntry = false;
		}
	catch (InputMismatchException e){
		System.out.print("\nPlease enter a number");
		//userEntry = true;
	}//end try catch
 
	}//end while repeat
 
	System.out.println("End Main");
    }//end main
 
 
}//end class

You need to add numberScan.next(); after line System.out.print("\nPlease enter a number"); in catch block. You can find more info from here https://stackoverflow.com/questions/...ext-or-nextfoo

Is a common mistake made by most of the beginner