CS Awesome - Unit 8 Vocabulary

2D Arrays

2d Array

2d Array

An array that holds items in a two dimensional grid. You can think of it as storing items in rows and columns (like a bingo card or battleship game). You can access an item (element) at a given row and column index.

2d Array Declaration

To declare an array, specify the type of elements that will be stored in the array, then ([][]) to show that it is a 2d array of that type, then at least one space, and then a name for the array. Examples: int[][] seats; String[][] seatingChart;

2d Array Creation

To create a 2d array, type the name and an equals sign then use the new keyword, followed by a space, then the type, and then [numRows][numCols]. Example: seatingChart = new String[5][4];. This will have 5 rows and 4 columns.

2d Array Index

You can access and set values in a 2d array using the row and column index. The first element in an array called arr is at row 0 and column 0 arr[0][0].

2d Array Initialization

You can also initialize (set) the values in the array when you first create it. In this case you don't need to specify the size of the array, it will be determined from the number of values that you specify. Example: String[][] seatingInfo = { {"Jamal", "Maria"}, {"Jake", "Suzy"}, {"Emma", "Luke"}}; This will create a 2d array with 3 rows and 2 columns.

2d Array Number of Rows

The number of rows (or height) is the length of the outer array. For an array arr use arr.length to get the number of rows in the array.

2d Array Number of Columns

The number of columns (or width) is the length of the inner array. For an array arr use arr[0].length to get the number of columns.

nested for loop

A for loop inside of another for loop. These are used to loop through all the elements in a 2d array. One loop can work through the rows and the other the columns.

out of bounds error

This happens when a loop goes beyond the last valid index in an array. Remember that the last valid row index is arr.length - 1. The last valid column index is arr[0].length - 1.