Thread: Hey! can anyone help me . i cant find an error (beginner)

hi, i m receiving error

Please help me. and do tell me where i was wrong
Thank you in advance

Welcome to National Database
Exception in thread "main" java.lang.NullPointerException
at general.main(general.java:46)

import java.util.Scanner;
public class general {
 
	String name;
	String fname;
	int dob;
	char sex;
	public general()
	{
		this("no","no",0,'n');
	}
 
	public general(String string, String string2, int i, char c) {
		// TODO Auto-generated constructor stub
	}
 
	protected void addgeninfo()
	{
		Scanner inp = new Scanner(System.in);
 
		System.out.println("Please Enter your name:");
		name=inp.next();
 
		System.out.println("Please Enter your Father's name:");
		fname=inp.next();
 
		System.out.println("Please Enter your dob(format:DDMMYYYY):");
		dob=inp.nextInt();
 
		String temp;
		System.out.println("Please Enter your sex(m/f):");
		temp=inp.next();
		sex =temp.charAt(0);
 
	}
 
	public static void main(String[] asgc)
	{
		int totnationals=10;
		System.out.println("Welcome to National Database");
		general nationals[] = new general[totnationals];
 
 
		for( int i =0; i <10; i++)
		{
			nationals[i].addgeninfo();
		}
 
 
	}
}

In Java (unlike C++) when you "create an array of objects," it actually just creates an array of reference types for that kind of object; it doesn't actually create the objects. (That concept takes a little getting used to. At least it did for me.)

Anyhow...

Try something like the following with your original code. (The error has nothing to do with the constructor.)

        general nationals[] = new general[...whatever...];
 
        for( int i = 0; i < nationals.length; i++) //<---It's better not to hard-code the size of the array as some constant.  Use the length member
        {
            nationals[i] = new general();
            // Now you have an object to deal with
            nationals[i].addgeninfo(); // Or whatever...
.
.
.

Once you get past the problem with null pointer exception, you can go back and flesh out the constructor so that it does what I think you had in mind.



Cheers!

Z