Declare Two-Dimensional Array - Clarification

Question

I am currently taking Java lessons, and the course is explaining two-dimensional arrays. The first method to declaring that type of variable would be to create a constant as arguments for how many rows and columns will be in my two-dimensional array. Then, I just used a nested for-loop to give random numbers to those particular rows, and columns.

The second method to declare AND initialize a two-dimensional array would be "int[][] nums" line below. I know that it has 3 rows. It's basically similar to putting a list in a bigger list, but how many columns are in the "nums" array? There may be a simple answer, but I am a little confused right now. Thank you for the assistance.

import java.util.Random; //Importing Class from Package

public class Chap15Part4
{
    public static void main(String[] args)
    {
        final int rows = 5; //Constant
        final int cols = 5; //Constant
        int[][] numbers = new int[rows][cols]; //Declaring 2-D Array with       constants as arguments
        Random rand = new Random(System.currentTimeMillis()); //Seeding Random Number Generator
        for(int r = 0; r < rows; ++r) //Nested for-loop to assign numbers to elements
            for (int c = 0; c < cols; ++c)
                numbers[r][c] = rand.nextInt(101); 

        int[][] nums = {{10,20,30,40}, {20,30,40,50}, {30,40,50,60}}; //Declaring & Initializing 2-D Array
    }

}

There are "four columns" in nums. However, keep in mind that a 2-dimensional array is simply an array where every element of that array is itself another array. So the structure need not be square. That is, nums[0] may be an array of size 3, but nums[1] may be an array of size 4 — Kon
– Kon, Commented Jun 10, 2015 at 16:07
4 columns...as every list as 4 elements. You can keep these small lists stacked and see it like {10,20,30,40} {20,30,40,50} {30,40,50,60} — Ouney
– Ouney, Commented Jun 10, 2015 at 16:08
Thank you for the help! I would say that you should read more about how nested for-loops work in order to better understand the first method, too. — Jeff Sours
– Jeff Sours, Commented Jun 10, 2015 at 17:02

haley · Accepted Answer · 2015-06-10 16:08:36Z

3

There are four columns. The matrix will look like this, so you can count the columns easily:

{{10, 20, 30, 40},
 {20, 30, 40, 50},
 {30, 40, 50, 60}}

answered Jun 10, 2015 at 16:08

haley

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Jeff Sours Over a year ago

Thank you! The way you typed it out makes a lot more sense.

River · Accepted Answer · 2015-06-10 16:08:45Z

1

There will be 4 columns as each sub-array item has 4 items.

Imagine stacking each item in brackets on top of the next so that the final array will look like:

10 20 30 40
20 30 40 50
30 40 50 60

answered Jun 10, 2015 at 16:08

River

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Jeff Sours Over a year ago

This was also very helpful. Thank you!

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