Array Declaration

[Arijit Ghosh]

A very simple and elementary doubt, but I guess very important for the Certification--
1. int[] i;
2. int[] i = new int[3];
3. Car[] i;
4. Car[] i = new Car[3];
System.out.println(i[0]);
What will be the output in each case ?
In which one is the Array DEFINED ?
In which one is the Array DECLARED ?
In which one is the Array INITILAIZED ?

[Ron Newman]

I may sound a bit like a broken record, but ... have you tried compiling and running a program with each of these alternatives?

[Arijit Ghosh]

Yes, I have and find that in case 1 and 3, compilation error is shown....
While in the other 2 cases, the default value is PRINTED.
In case 2, it is 0 and in case 4 it is null, as it should be.
I read that whether an array is declared or initialized, in both the cases, the array elements are initialized to default values.
So assuming Case 1 and 3 are DECLARATION cases, so when I try to print the element values, it should show the default values as in case 2 and 4.
Am I missing something ?

[Ron Newman]

Local variables in methods are NOT initialized by default.

[Arijit Ghosh]

What happens if it is not local variable but is a member variable ? I can create a non-static member variable and then try to print an element of that array as shown...

package ch01;
class ArrayInstanceVariable {
int[] j;
public static void main(String args[]) {
ArrayInstanceVariable aiv = new ArrayInstanceVariable();
int[] i = new int[2];
System.out.println("i[0] >> "+i[0]);
System.out.println("j[0] >> "+aiv.j[0]);
}
}

It gives Null Pointer exception... Why ?
[ November 25, 2002: Message edited by: Arijit Ghosh ]

[Anup Katariya]

if u write your member variable as
int j[] = new int[3];
then it wont give any errors.
You are confused between array reference and array elements.

[Ron Newman]

int[] j; // is initialized to a null reference
Unless and until you assign something to j, any reference to j[0] will cause a NullPointerException.

[Jose Botella]

Arijit, this is the problem:

I read that whether an array is declared or initialized, in both the cases, the array elements are initialized to default values.

The variable declared as an array follows the same path regarding intialization as any reference variable. It would be initialized to null if it was declared as a field of the object. Being a local variable it will not be initialized by its mere declaration. However the elements of the array are another story. Whenever the array is created, either as a member or local to a method, its elements will be initialized to its corresponding default value.

[Arijit Ghosh]

Thanks everyone...