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1

2D Arrays

Arrays that have rows and columns, forming a grid-like structure.

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2

Array of Arrays

A 2D array

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3

Rows length

The number of rows in a 2D array, accessed using arrayName.length.

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4

Columns length

The length of the first column in a 2D array, accessed using arrayName[0].length.

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5

Indexes

Positions in a 2D array

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6

Initialize a 2D array by elements

`int[][] numbers = {{1,2,3,4},{5,6,7,8}};`

This would create the two-dimensional array with first row as array [1, 2, 3, 4] and second row as array [5, 6, 7, 8].

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7

Initialize a 2D array by size

`int[][] numbers = new int[2][2];`

numbers[0][0] = 0;

//...

This would create the two dimensional array with 2 rows and 2 columns. Then you can set the values of individual elements using the row and column index.

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8

How do you access an element of a 2D array?

Use the row index (r), then the column index (c), as shown.

Example: Access element in second row, first column. This would print “5”.

`int[][] numbers = {{1,2,3,4},{5,6,7,8}};`

System.out.print(numbers[1][0]);

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9

What index does any array start at?

0

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10

What index does an array end at?

array.length - 1

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