Array length in a multidimensional array java

Question

I'm having difficulties understanding why once i declare a multidimensional array like :

int t2[][] = new int[5][10] ;

I can still change the length of the arrays like so :

t2[0] = new int[12];

I thought once we declare the array to be a certain length we can't change it. So how is it possible here ?

You can do this with a single dimension too: int[] t = new int[5]; t = new int[12];. — Oliver Charlesworth
– Oliver Charlesworth, Commented Nov 18, 2017 at 12:55
You're simply not changing the array. Instead, you are creating a new array, with a new length. — Marco13
– Marco13, Commented Nov 18, 2017 at 12:56

Joe C · Accepted Answer · 2017-11-18 12:58:09Z

5

Fundamentally speaking, a two-dimensional array is nothing more than an array of arrays. So this:

int t2[][] = new int[5][10] ;

is really doing this:

int t2[][] = new int[5][];
for (int i = 0; i < t2.length; i++)
{
    t2[i] = new int[10];
}

Thus in reality, you can assign t2[x] in the same way as you're assigning any other array element.

NOTE: You are not extending the length of the array by saying t2[0] = new int[12]. You are creating a new one, which means that if you have done any assignments to t2[0][x], then they will be lost unless you copy them over yourself.

answered Nov 18, 2017 at 12:58

Joe C

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