Array Of Objects

[Ajay Divakaran]

There are no compilation errors, but when i run the program I get an NullPointerException in the indicated line below. How do I rectify this?

class A
{
int i,j;
}
public class ArrayObjects
{
public static void main( String args[] )
{
A ob[]= new A[5];
for( int i=0; i<5; i++ )
{
ob[i].i=1; //NullPointerException
ob[i].j=2;
}
}
}

[Ernest Friedman-Hill]

The array is made up of five variables that can refer to A objects. Each of these five variables is null when you construct the array. If you want five objects, then you must construct each one individually and add it to the array -- i.e.,

ob[i] = new A();

Note that rather than having exposed member variables and setting them after constructing an object, it's good practice to provide a constructor to initialize the members, i.e.,

ob[i] = new A(1, 2);