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

[fredsilvester93]

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();
		}
 
 
	}
}

[Fubarable]

A NullPointerException (NPE) means that you are trying to use a variable that has not been initialized yet. The exception will tell you which line of your code is causing the error, and so you'll need to inspect that line, find the offending variable, search in your code and see where you think you might be initializing it but in fact are not.

Edit: I'd look at that constructor of yours where you think you might be initializing class fields, but in fact are not. You might want to fill in the body of that constructor with a little bit of code.

[fredsilvester93]

i cant find any errr when i remove array it works properly.. bt it is nt working properly whn i create array of object

[Zaphod_b]

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