Two –Dimensional Arrays Mrs. C. Furman Java Programming November 19, 2008

Two Dimensional Arrays  rows and columns, also called a Matrix  we must specify the number of row and columns we will need when we construct the 2DArray. Similar to Arrays. Example: int [][] magicSquare = new int [4][4];

Accessing Elements in a 2D Array  Elements are indexed [row][column] magicSquare [0][0] = 3; magicSquare [1][3] = 5; int myNum = magicSquare [1][3];

Initializer List for 2D int [][]cars = {{10, 7, 12, 10, 4}, {18, 11, 15, 17, 10}, {18, 11, 15, 17, 10}, {12, 10, 9, 5, 12}, {12, 10, 9, 5, 12}, {16, 6, 13, 8, 3}}; {16, 6, 13, 8, 3}}; GM Ford Toyota BMW red brown black white gray

Getting Size .length gives us the number of rows… then when we access a specific row, we do.length to get number of columns.  int[][] list = {{1,2,3, 4}, {1}, {1, 2, 3}};  int numRows = list.length;//3  int firstCol = list[0].length;//4  int secCol = list[1].length;//1  int thirdCol = list[2].length;//3

Looping Through a 2D Array Example 3: Write a nested for loop to output all elements in the 2D array. for (int row = 0; row < list.length; row++) { for (int col = 0; col< list[row].length; col++) { System.out.print (list [row][col] + “ “); } System.out.println (); }

Multiplication Table  Write a loop that will assign a 5 x 5 2D Array to the multiplication tables of The result will look like the below 2D Array

Picture Encoding  Bitmap images: each dot or pixel is represented separately.  Pictures are 2-D arrays of pixels.  We will be dealing with.jpg (jpeg) files  Each pixel in a picture has a color  The dimension of the picture is measured in pixels.

JPEG’s  High quality pictures with smaller storage.  JPEG is a lossy compression format.  Lossy compression: it is compressed, made smaller, but not with 100% of the quality of the original.  Typically what gets thrown out is the stuff that you don’t see or notice anyway, so the quality is still considered high.

Color  RGB color model.  Pixels are encoded with three numbers, 1 st for the amount of red, 2 nd for the amount of green, and 3 rd for the amount of blue  We can make any humanly visible color by combining different amounts of red, green and blue.  Combining all 3 together to get white, remove all 3 to get black.  (0,0,0) – black; (255, 255, 255) - white

Some Color examples  (255, 0, 0) – red  (100, 0, 0) – darker red  (0, 100, 0) – dark green  (0, 0, 100) – dark blue  All 3 the same… we get gray…  (50, 50,50) – dark gray  (150, 150, 150) – lighter gray