Summary
2D Arrays Summary: 8.3.0
- You learned about
two dimensional arrays
- Stores objects in a 2D table
- Creates an array of arrays
- Learned how to declare, create, and access 2D arrays and their elements
- Array elements are accessed using row and column indices
- First element is at [0][0]
Concept Summary: 8.3.1
- 2D array
- An array which holds items in a 2d grid
- you can access an item using a row and column index
- 2D Array declaration
- You can declare an array by specifying the type, then
[][]
, then a name int[][] seats;
String[][] seatingChart;
- You can declare an array by specifying the type, then
- 2D array creation
- Create a 2D array by typing the name and an equals sign
- use
new
keyword, then the type, and the number of rows and columns seatingChart = new String[5][4];
- 2D Array Index
- You can access and set values in a 2D array using a row and column index
arr[0][0]
- 2D Array Initialization
- You can initialize a 2D Array when you create it
- The size is automagically determined
int[][] myInt = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}};
- 2D array number of rows
- The length of the outer array
arr.length
- 2D array number of columns
- The length of an inner array
arr[0].length
- nested for loop
- A for loop inside another for loop
- out of bounds error
- when a loop goes beyond the last valid index in an array
- the last valid row is arr.length - 1!
- when a loop goes beyond the last valid index in an array
Common Mistakes: 8.3.3
- Forgetting to create an array; only declaring it
- Using 1 as the first index
- is 0
- using
array[0].length
as the last valid column- not
array[0].length - 1
- not
- using
array.length()
instead ofarray.length
- going out of bounds when looping through an array
- Throws an
ArrayIndexOutOfBoundsException
!
- Throws an
- Jumping out of a loop using a return statement before the end of the loop
- using the incorrect starting or ending indices
- using
array.length
for both rows and columns- use
array[0].length
for columns
- use
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
This was adapted from the CS Awesome curriculum, which was created by
Barbara Ericson, Beryl Hoffman, and many other CS Awesome contributors. All rights reserved.
CS Awesome is licensed under CC BY-NC-SA 4.0.