// ParseIntException.java
// Class demo by THC to show a simple exception.

import java.util.Scanner;

public class ParseIntException {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    
    while (true) {
      System.out.print("Enter a number: ");
      String s;
      s = input.nextLine();
      int i = 0;

      // The following line just lets the default NumberCaughtException
      // occur if s contains non-digits.
      // i = Integer.parseInt(s);

      // The following lines catch the exception.
      try {
        i = parseInt(s); // remove Integer. to call the method below
      }
      catch (NumberFormatException e) {
        System.out.println("Caught exception: " + e.getMessage());
      }

      System.out.println("You entered " + i);
    }
  }

  // We could write parseInt ourselves.
  public static int parseInt(String s) {
    int value = 0; // integer value to be returned

    // Go through each character of s.
    for (int i = 0; i < s.length(); i++) {
      char c = s.charAt(i);
      if (c >= '0' && c <= '9') // do we have a digit?
        value = (value * 10) + (c - '0'); // yes, so update value
      else
        throw new NumberFormatException(s); // no, so throw exception
    }

    return value;
  }
}