Thread: Scanner Problem

Hello guys,

I wrote a code from thomas wu book (OOP java, 5 edition).
But I got an error in scanner statement like this

debug:
Your Age : 
Exception in thread "main" java.lang.NullPointerException
	at ProgrammerDefinedException.AgeInput5.getAge(AgeInput5.java:41)
	at ProgrammerDefinedException.Ch8TestAgeInput5.main(Ch8TestAgeInput5.java:11)
Java Result: 1
BUILD SUCCESSFUL (total time: 3 seconds)

there's my code (I have given a mark where the error)

/*
 * Buku Thomas Wu, Bab Programmer Defined Exception
 * Self Independent Declaration Modified Class
 */
package ProgrammerDefinedException;
import java.util.Scanner;
import java.util.InputMismatchException;
 
public class AgeInput5 {
    private static final String DEFAULT_MESSAGE = "Your Age : ";
    private static final int DEFAULT_TEPI_BAWAH = 0;
    private static final int DEFAULT_TEPI_ATAS = 99;
 
    private int tepiBawah;
    private int tepiAtas;
 
    private Scanner scanner;
 
    /***Constractor***/
    public AgeInput5(int low,int high)  {
        init(DEFAULT_TEPI_BAWAH,DEFAULT_TEPI_ATAS);
    }
 
    public AgeInput5(String msg,int low,int high) throws IllegalArgumentException{  //Throwing Exception
        if(low>high)
            throw new IllegalArgumentException("tepi bawah "+low+" lebih besar dari tepi atas "+high);
        else
            init(low,high);
        }
 
    /***Methode***/
    public int getAge() throws AgeInputException{
        return getAge(DEFAULT_MESSAGE);
    }
 
    public int getAge(String msg) throws AgeInputException{
        int umur;
        while(true){
          System.out.println(msg);
          try{
              umur = scanner.nextInt(); <=========================================THIS IS AN ERRROR
              if(umur<tepiBawah||umur>tepiAtas)
                  throw new AgeInputException(tepiBawah,tepiAtas,umur);
              return umur;
          }
          catch(InputMismatchException e){
              scanner.next();
              System.out.println("Input is invalid \n" + "Please enter digit Only");
 
          }
        }
    }
 
    private void init(int low,int high){
        tepiBawah=low;
        tepiAtas=high;
    }
}

Are you guys know where's my mistake?
thanks btw.

Hi

I know it's umur, so what should I do? assign the value of var umur before I scan it?

Thanks

I see..
this is a statement at line 41

umur = scanner.nextInt()


thanks

ohh,, scanner is an object on that line and scanner doesn't have any value before.
so scanner have NULL value and umur take NULL value from it right?
so how should I do for solve it, I mean I want umur have a value from user input.

Thansk Norm I got it fixed.
like you said we just need scanner have the addres, so we initialize .
scanner= new Scanner(System.in);