Question

This is the scenario:

class A{
int a;
}

class B{
A objectA[]=new A[10] ;
}

class C{
B ObjectB;
public static void main(String[] args){
ObjectB.ObjectA[0].a=1;
}
}

I get a nullpointerexception in main operation. However if I declare just one object of class A, I don’t get the error. Why so? How do I rectify it?

Answer 1

calling new B() initializes an array of objects of type A, but none of the member objects. You can rectify it first initializing objectB and then calling objectA[i] = new A() for each item in the array.

class B{
    A objectA[]=new A[10] ;
    {
        for (int i = 0; i < 10; i++)
            objectA[i] = new A();
    }
}

class C{
B ObjectB = new B();
public static void main(String[] args){
ObjectB.ObjectA[0].a=1;
}
}