How do I create a jagged 2d array in Java?

Question

Our homework assignment asks us to use a jagged array to store the values of a two dimensional boolean matrix. Is there a built in java class for the jagged array or am I going to have to manually create it with an Array of ArrayLists?

NPE · Accepted Answer · 2012-04-22 19:54:44Z

16

In Java, a 2D array is an array of 1D array objects. Each 1D array can have different length, which means that you get jagged arrays out of the box.

For example, the following is perfectly valid Java, and prints out 3 5 3 4:

    int x[][] = {{0,1,2,3,4},{0,1,2},{0,1,2,3}};
    System.out.println(x.length);
    System.out.println(x[0].length);
    System.out.println(x[1].length);
    System.out.println(x[2].length);

answered Apr 22, 2012 at 19:54

NPE

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2 Comments

Lilluda 5 Over a year ago

So if i need to add more elements to these indiviuals arrays i would have to resize x[1] for example instead of just x?

NPE Over a year ago

@Chris: Yes. For example x[1] = Arrays.copyOf(x[1], newLength);

Community · Accepted Answer · 2017-05-23 12:33:51Z

0

It actually sounds like you might want a sparse matrix implementation. You can get much better performance out of it if you are having to modify the matrix. Array copy operations are pretty expensive. Sparse matrices / arrays in Java

edited May 23, 2017 at 12:33

CommunityBot

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answered Apr 22, 2012 at 20:21

Jason Clawson

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