Java - Creating 2D Array with same size as another 2D Array

Question

I have the following 2D Array:

     int[][] matrixA = { {1, 2 ,3}, {4, 5, 6} };

And I want to create another 2D Array with the same size of matrixA, my question is how do I do it with, the same way of an ordinary array, i.e, int[] arrayA = {10, 12, 33, 23}, int[] arrayB = new int[arrayA.length]

    int[][] matrixB = new int[matrixA.length][]

Can I do it like this, only alocating one array with two positions and and leaving the rest to be filled with a for loop? Or there's a more correct and flexible way to do this?

check this out.

cosh
– cosh

2018-01-31 23:42:26 +00:00
Commented Jan 31, 2018 at 23:42 — cosh
– cosh, Commented Jan 31, 2018 at 23:42

Andrey Tyukin · Accepted Answer · 2018-01-31 23:57:37Z

7

Why not just use the ordinary multidimensional array initialization syntax?

    int[][] a = {{1,2,3}, {4,5,6}};
    int[][] b = new int[a.length][a[0].length];

This seems to work perfectly well. Here is a little loop that tests that all entries are indeed present, and that we don't get any AIOOBEs:

    for (int i = 0; i < a.length; i++) {
        for (int j = 0; j < a[0].length; j++) {
          b[i][j] = a[i][j];
        }
    }

This, obviously assumes that you are dealing with rectangular matrices, that is, all rows must have the same dimensions. If you have some weird jagged arrays, you must use a loop to initialize each row separately.

answered Jan 31, 2018 at 23:57

Andrey Tyukin

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3 Comments

ramireeez Over a year ago

Hmm i see... but what does the [a[0].length] in terms of coding? I'm just trying to understand it completely, and not just copy and paste it. Thanks!

Andrey Tyukin Over a year ago

a is a two-dimensional array. a[0] is the first "row" (if you think in row-major format). a[0].length is the dimension of the first row, that is, the width of the matrix. a.length would be the height of the matrix. new MyType[h][w] is the usual way to initialize two-dimensional arrays in Java. Well "usual"... Usual in those rare contexts where you initialize arrays in Java (it doesn't happen too often, because collections, and now also the stream-api, are vastly more comfortable to use).

ramireeez Over a year ago

Ok so if, for instance, I wanted to switch the columns for the rows of a[] to intialize b[], it should be like this, `int[][] b = new int[a[0].length][a.length]?

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