Chapter 8 Arrays and the arraylist class 3

Chapter 8 Chapter 8 Arrays and the ArrayList Class Multi Dimensional Arrays 2 Contents I Two Dimensional Arrays II Arrays with Three or More Dimensions 3 I Two Dimensional Arrays 1 Creating a Two Dime.

Chapter 8

Arrays and the ArrayList Class

Multi-Dimensional Arrays

Contents

I Two-Dimensional Arrays

II Arrays with Three or More Dimensions

I Two-Dimensional Arrays

1 Creating a Two-Dimensional Array

2 Initializing a Two-Dimensional Array

3 The length Field in a Two-Dimensional Array

4 Displaying All the Elements of a

Two-Dimensional Arrays

5 Summing All the Elements of a

Two-Dimensional Array

6 Summing the Rows of a Two-Dimensional

Array

I Two-Dimensional Arrays

7 Summing the Columns of a Two-Dimensional Array

8 Passing Two-Dimensional Arrays to Methods

9 Ragged Arrays

I.1 Creating a Two-Dimensional

Array

Two-dimensional array, which are sometimes

called 2D arrays, is an array of arrays

It has rows and columns of elements

Row 0 Row 1 Row 2

Column

0 Column 1 Column 2 Column 3

I.1 Creating a Two-Dimensional

Array

To declare a two-dimensional array:

double[][] scores = new double[3][4];

Two set of brackets

Two size declarators

The first one is for the number of rows: 3

The second one is for the number of columns: 4

Two sets of brackets

indicate

a two-dimensional

array

Number of rows

Number of columns

I.1 Creating a Two-Dimensional

Array

In the scores array:

The elements in row 0:

 The elements in row 1:

 The elements in row 2:

I.1 Creating a Two-Dimensional

Array

scores[0][0] scores[0][1] scores[0][2] scores[0][3] scores[1][0] scores[1][1] scores[1][2] scores[1][3] scores[2][0] scores[2][1] scores[2][2] scores[2][3]

Row 0 Row 1 Row 2

Column

address

The scores

variable

I.1 Creating a Two-Dimensional

Array

Programs that process two-dimensional arrays

can do so with nested loops

final int ROWS = 3;

final int COLS = 4;

double[][] scores = new double[ROWS][COLS];

for(int row = 0; row < ROWS; row++) {

for(int col = 0; col < COLS; col ++) {

System.out.print(“Enter a score: “);

scores[row][col] = keyboard.nextDouble();

}

}

I.2 Initializing a Two-Dimensional

Array

Enclose each row's initialization list in its own set

of braces:

int[][] numbers = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} };

I.3 The length Field in a

Two-Dimensional Array

A two-dimensional array can be considered as an array of one-dimensional arrays

int[][] numbers = new int[3][4];

addres s addres s addres s

numbers[1][1] numbers[1][2] numbers[1][3] numbers[1][0]

numbers[0][1] numbers[0][2] numbers[0][3] numbers[0][0]

numbers[2][1] numbers[2][2] numbers[2][3] numbers[2][0]

numbers[

0]

numbers[

1]

numbers[

2]

address

The numbers

variable numbers.length 3

numbers[0].length 4

numbers[1].length 4

numbers[2].length 4

I.3 Displaying All the Elements of

a Two-Dimensional Array

int[][] numbers = { {1, 2, 3, 4},

{4, 5, 6, 8}, {9, 10, 11, 12} };

//Display all the elements in the array

for(int row = 0; row < 3; row++) {

for(int col = 0; col < 4; col++)

System.out.println(numbers[row][col]);

}

//A better approach to display all elements in the array

for(int row = 0; row < numbers.length; row++) {

for(int col = 0; col < numbers[row].length; col++)

System.out.println(numbers[row][col]);

}

I.4 Summing All the Elements of

a Two-Dimensional Array

int[][] numbers = { {1, 2, 3, 4},

{4, 5, 6, 8}, {9, 10, 11, 12} };

int acc = 0; //Accumulator, set to 0

//Sum the array elements

for(int row = 0; row < numbers.length; row++) {

for(int col = 0; col < numbers[row].length; col++)

acc += numbers[row][col];

}

//Display the sum

System.out.println(“The total is ” + acc);

I.5 Summing the Rows of a

Two-Dimensional Array

Calculate the sum of each row in a

two-dimensional array:

int[][] numbers = { {1, 2, 3, 4},

{4, 5, 6, 8}, {9, 10, 11, 12} };

int acc; //Accumulator

for(int row = 0; row < numbers.length; row++) {

//Set the accumulator to 0

acc = 0;

//Sum a row

for(int col = 0; col < numbers[row].length; col++)

acc += numbers[row][col];

//Display the sum

System.out.println(“The total of row is ” + acc);

}

I.6 Summing the Column of a

Two-Dimensional Array

The outer loop controls the column subscript and the inner loop controls the row subscript

int[][] numbers = { {1, 2, 3, 4},

{4, 5, 6, 8}, {9, 10, 11, 12} };

int acc; //Accumulator

for(int col = 0; col < numbers[0].length; col++) {

//Set the accumulator to 0

acc = 0;

//Sum a column

for(int row = 0; row < numbers.length; row++)

acc += numbers[row][col];

//Display the sum

System.out.println(“The total of column is ” + acc);

}

I.7 Passing Two-Dimensional

Arrays to Methods

When a two-dimensional array is passed to a

method, the parameter must be declared as a

reference to a two-dimensional array

public static void showArray(int[][] array)

The method's parameter, array, is declared as

a reference to a two-dimensional array.

I.8 Ragged Arrays

When the rows of a two-dimensional array are of different lengths, the array is known as a ragged array

Creating a ragged array:

//Creating a two-dimensional array, the array has

four

//rows, but the rows have not yet been created.

int[][] ragged = new int[4][];

//Creat the individual rows

ragged[0] = new int[3]; //row 0 has 3 elements

ragged[1] = new int[4]; //row 1 has 4 elements

ragged[2] = new int[5]; //row 2 has 5 elements

ragged[3] = new int[6]; //row 3 has 6 elements

I.8 Ragged Arrays

Processing elements of a ragged array:

for(int row = 0; row < ragged.length; row++)

{

for(int col = 0; col < ragged[row].length; col++) {

// Processing the element ragged[row][col]

//

}

}

II Arrays with Three or More

Dimensions

Java does not limit the number of dimensions that

an array may have

A three-dimensional array declaration:

double[][][] array = new double[3][5][7];

This array can be though of as three sets of five rows

Each row contains seven elements