This week's book giveaway is in the Jobs Discussion forum.
We're giving away four copies of Java Interview Guide and have Anthony DePalma on-line!
See this thread for details.
The moose likes Programmer Certification (SCJP/OCPJP) and the fly likes Array Sizes Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login

Win a copy of Java Interview Guide this week in the Jobs Discussion forum!
JavaRanch » Java Forums » Certification » Programmer Certification (SCJP/OCPJP)
Bookmark "Array Sizes" Watch "Array Sizes" New topic

Array Sizes

Dale DeMott
Ranch Hand

Joined: Nov 02, 2000
Posts: 515
If I have something like this...
int myInt [][] = new int [3][];
What are the total number of elements in this array. It looks as if its zero. Is it possible to initialize the second array later?

By failing to prepare, you are preparing to fail.<br />Benjamin Franklin (1706 - 1790)
Valentin Crettaz
Gold Digger

Joined: Aug 26, 2001
Posts: 7610
Yup that's possible. Consider this:
int[][] iArray = new int[2][];
iArray[0] = new int[2];
iArray[1] = new int[10];
This way you can have an array of array of different lengths, which can be useful sometimes..
In this case the total number of elements is 12 (2+10)
[ February 22, 2002: Message edited by: Valentin Crettaz ]

[Blog] [Blogroll] [My Reviews] My Linked In
Brian Lugo
Ranch Hand

Joined: Nov 10, 2000
Posts: 165
To answer your first question:
When you execute this statement:
int myInt [][] = new int [3][];
You are creating a two dimensional array with the size of one dimension as 3 that contains null refrences to the other dimension, i.e. even though you are specifying one dimension as 3, this dimension of the array is not initialized with the default primitve values (0 in this case of integer) - it is initialized with null references to the second dimension.
Try out the following code to understand what I am trying to say:

So, I would say there are 3 null references in the array in your example and 5 null references in my example. I do not know if you can classify them as array elements. The array certainly does not have default integer primitive values, i.e. zeroes.
PS - I just came up with this sentence:
"In a partially constructed primitive multi dimensional array, the dimension that is fully constructed contains null references to the dimension that is not fully constructed. It does not contain default primitive values"
Feel free to correct this statement, keeping in mind my post.
[ February 22, 2002: Message edited by: Brian Lugo ]
[ February 22, 2002: Message edited by: Brian Lugo ]
Rajinder Yadav
Ranch Hand

Joined: Jan 18, 2002
Posts: 178
Here is small program I worte to show you what to expect

You may be surprised for the value you get for a.length and ch.length!
a.length = 2
a[0].length = 5
a[1].length = 5
ch.length = 2
ch[0].length = 8
ch[1].length = 12

<a href="" target="_blank" rel="nofollow">Rajinder Yadav</a><p>Each problem that I solved became a rule which served afterwards to solve other problems. --Rene Descartes
I agree. Here's the link:
subject: Array Sizes
jQuery in Action, 3rd edition