How do I allocate an array of arrays in Java?

Question

I want to dynamically allocate memory for an array of arrays, knowing that the number of rows is going to be n, but I don't want to allocate more memory for each row than needed, which is going to be i = 1:n, number of elements = i for each row, and I know this in advance.

    int [] a = new int[n];
    for (int i=0; i<n; i++)

I have just started to learn Java, and I'm new to this. As far as I know, the first line will allocate memory for n elements (number of rows), and what I want to do is create a new array of i elements at each iteration.

You should prefer using ArrayList if you need dynamism in size, although arrays perform better than ArrayList — Pushpesh Kumar Rajwanshi
– Pushpesh Kumar Rajwanshi, Commented Oct 12, 2018 at 6:51
Possible duplicate of How to make an array of arrays in Java — teppic
– teppic, Commented Oct 12, 2018 at 7:24

dehasi · Accepted Answer · 2018-10-12 06:52:36Z

5

You can declare a two-dimensional array and allocate the first dimensional

  int [][] a = new int[n][];

And then, inside a loop, you can allocate the second one

 for (int i=0; i<n; i++)
   a[i] = new int[necessary_length];

But if you know the size in advance you obviously can declare it in the beginning

  int [][] a = new int[n][n];

answered Oct 12, 2018 at 6:52

dehasi

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