CMSC 150MULTI-DIMENSIONAL ARRAYS

CS 150: Mon 27 Feb 2012

Motivation

A digital image is a two-dimensional collection of pixels (picture elements)

Each pixel has an associated color (green, brown, pink, yellow)

Taken collectively, the pixels form the image

Motivation

Motivationpixel

2D Array can be primitive or class type

Syntax: type[][] variableName; type[][] variableName = new type[numRows]

[numCols];

Examples:Color[][] pixels = new Color[100][256];boolean[][] missingTeeth = new boolean[2][16];String[][] firstLastNames = new String[NUM_STUDENTS][2];

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

In Memory myArray null

In Memory 0x12AB79

[0][0][0][1]

[0][2]

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[1][0][1][1]

[1][2]

In Memory 0x12AB79

[0][0][0][1]

[0][2]

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[1][0][1][1]

[1][2]

row 0

row 1

In Memory 0x12AB79

77

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

In Memory 0x12AB79

77

42

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

In Memory 0x12AB79

77

42

101

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

In Memory 0x12AB79

77

42

101

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

154

In Memory 0x12AB79

77

42

101

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

154

84

In Memory 0x12AB79

77

42

101

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

154

84

202

In Memory 0x12AB79

77

42

101

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

154

84

202

myArray[0]

myArray is an int[][]

myArray[0] is an int[]

myArray[0][0] is an int

In Memory 0x12AB79

77

42

101

public class 2DArrayExample{

public static void main(String[] args)

{int[][] myArray;

myArray = new int[2][3];

myArray[0][0] = 77;myArray[0][1] = 42;myArray[0][2] = 101;

myArray[1][0] = 77 + 77;myArray[1][1] = 42 + 42;myArray[1][2] = 101 + 101;

}}

myArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

154

84

202

myArray[1]

myArray is an int[][]

myArray[1] is an int[]

myArray[1][0] is an int

In Memory 0x12AB79

public class 2DArrayExample{ public static void main(String[] args) { String[][] strArray;

strArray = new String[2][3];

for (int i = 0; i < strArray.length; i++) { for (int j = 0; j < strArray[i].length; j++) { strArray[i][j] = new String((i+1) + “ and “); }

}}

strArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

0x33DB26

0x33DC01

0x33DD25

0x33DE04

0x33DE29

0x33DF22

In Memory 0x12AB79

public class 2DArrayExample{ public static void main(String[] args) { String[][] strArray;

strArray = new String[2][3];

for (int i = 0; i < strArray.length; i++) { for (int j = 0; j < strArray[i].length; j++) { strArray[i][j] = new String((i+1) + “ and “); }

}}

strArray

[0][0][0][1]

[0][2]

[1][0][1][1]

[1][2]

0x33DB26

0x33DC01

0x33DD25

0x33DE04

0x33DE29

0x33DF22

# rows

# cols

Managing 2D Arrays Typically use nested for loops:int[][] randomNumbers = int[1024][2048];

for (int i = 0; i < randomNumbers.length; i++){ for (int j = 0; j < randomNumbers[i].length; j++) { randomNumbers[i][j] = generator.nextInt(10000); }}

Managing 2D Arrays Typically use nested for loops:int[][] randomNumbers = int[1024][2048];

for (int i = 0; i < randomNumbers.length; i++){ for (int j = 0; j < randomNumbers[i].length; j++) { randomNumbers[i][j] = generator.nextInt(10000); }}

int numberOfOdds = 0;for (int i = 0; i < randomNumbers.length; i++){ for (int j = 0; j < randomNumbers[i].length; j++) {

if ( randomNumbers[i][j] % 2 != 0 ) { numberOfOdds++; } }}

Let’s Try Some…

Photo by Gary Mueller, from www.allaboutbirds.org (Cornell Laboratory of Ornithology)