object array..... help

[sudharshiya mohan]

my program is as below and i m getting NullPointerException . how to create an array for object.



import java.io.*;
import java.util.*;
import java.lang.*;
class AccessPoint
{
public void display()throws IOException
{
int x=388,y=560;

System.out.println("accesspoint is located at ("+x+","+y+")");
}

}
class Ex
{
public static void main(String args[]) throws IOException
{

AccessPoint ap[] = new AccessPoint[5];
for(int j=0;j<5;j++)
ap[j].display();

}
}

[Nadeem Awad]

Dear sudharshiya,
You've created an array of AccessPoint object references, but the objects themselves are not created yet. You need to insert the following line in the for loop:

    
public static void main(String args[]) throws IOException {
AccessPoint ap[] = new AccessPoint[5]; 
for(int j=0;j<5;j++) {
[B]ap[j] = new AccessPoint();[/B]
ap[j].display();    
}
}

And by the way, the IOException is never thrown from the display method, so you don't need to declare it.

[marc weber]

Just to expand on what Nadeem said: When you create the array with "new AccessPoint[5]," you have an array object. But until you assign AccessPoint instances, all the reference elements within the array have a default value of null. Therefore, the problem occurs when you try to dereference one of these null values with "ap[j].display();"

[sudharshiya mohan]

thanks for your reply. it helped me alot