Chapter 8 Multidimensional Arrays

Question 1

What is the syntax for declaring an array reference variable:

Answer 1

dataType[][] refVar;

[][] is the # of dimensions you want

Question 2

Create an arrayand assign its reference to variable

Answer 2

refVar = new dataType[10][10];

Question 3

Combine declaration and creation in one statement (row = 10, col = 10):

Answer 3

dataType[][] refVar = new dataType[10][10];

Question 4

Declaring variables of two dimensional arrays[10][10] and creating two dimensional arrays syntax

Answer 4

int[][] matrix = new int[10][10];
or
int matrix [] [] = new int[10][10];

Question 5

Access an element of a 2D array:

Answer 5

matrix[0][0] = 3;

Question 6

Assign each element of the array a random number:

Answer 6

for (int i = 0; i < matrix.length; i++){
for (int j = 0; j < matrix[i].length; j++){
matrix[i][j]; = (int)(Math.random() * 1000);

Question 7

Declare, initialize, and create a two dimensional array with 3 rows and 3 columns with values ascending from 1-12.

Answer 7

int[][] array = {
{1,2,3}
{4,5,6}
{7,8,9}
{10,11,12}
}
;

Question 8

How would you express a two dimensional array with 3 rows and 4 columns

Answer 8

int[][] x = new int[column][row];

ex.
int[][] x = new int[3][4]

Question 9

Array start at array[0].length. Calling beyond the index causes:

Answer 9

ArrayIndexOutOfBoundsException

Question 10

Ragged arrays definition

Answer 10

Each row in a two dimensional array is itself an array, so each row can have different lengths.

Not a solid block, like an increasing or decreasing triangle

Question 11

Declare and initialize a random array syntax with 5– rows and 4 cols with values {1,2,3,4,5}, {2,3,4,5}, {3,4,5}, {4,5}, [5}.

Answer 11

int[][] matrix = {
{1,2,3,4,5}
{2,3,4,5}
{3,4,5}
{4,5}
{5}
}
};

Question 12

7 ways of processing arrays

Answer 12

1. Initializing arrays with input values
2. Printing arrays
3. Summing all elements
4. Summing all elements by column
5. Which has the largest sum
6. Finding the smallest index of the largest column
7. Random Shuffling

Question 13

Initializing arrays with input values:

Answer 13

import java.util.Scanner;

Scanner input = new Scanner(System.in);

System.out.println(“Enter “ + matrix.length + “ rows and “ + matrix[0].length + “columns: “);

for (int row = 0; row < matrix.length; row++){
for (int col = 0; col < matrix[row].length; col++){
matrix[row][col] = input.nextInt();
}
}

Question 14

Printing arrays

Answer 14

for (int row = 0; row < matrix.length; row++){
for(int col= 0; col < matrix[row].length; col++){
System.out.print(matrix[row][col] + “ “);
}
System.out.println();
}

Question 15

Summing all elements

Answer 15

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

Question 16

Summing elements by column:

Answer 16

for (int col = 0; col < matrix[0].length; col++){
int total = 0;
for(int row = 0; row < matrix.length; row++){
total += matrix[row][col];
System.out.println(“Sum for column “ + col + “ is “ + total);
}

Question 17

Random Shuffling

Answer 17

for (int i = 0; i < matrix.length; i++){
for(int j = 0; j < matrix[i].length; j++){
int i1 = (int)(Math.random() * matrix.length);
int j1 = (int)(Math.random() * matrix[i].length);

// Swap matrix [i][j] with matrix [i1][j1]
int temp = matrix[i][j];
matrix[i][j] = matrix[i1][j1];
matrix[i1][j1] = temp;
}
}

Question 18

A two dimensional array can be used to store a:

Answer 18

table

Question 19

A variable for two dimensional arrays can be declared using the syntax:

Answer 19

elementType[][] arrayVar =

Question 20

Each element in a two dimensional array is represented using the syntax:

Answer 20

array-Var[rowIndex][columnIndex];

Question 21

You can create and initialize a two-dimensional array
using an array initializer withthe syntax: (shorthand notation)

Answer 21

elementType[][] arrayVar = {{row values}, . . ., {row values}}.

Question 22

You can use arrays of arrays to form multidimensional arrays. For example, a variable for three-dimensional arrays can be declared as

Answer 22

elementType[][][] arrayVar and a three-dimensional array can be created using new elementType[size1][size2] [size3].

Question 23

//create your first 2 dimensional array of
// 5 rows of values holding 5 values each

//access length of the array

// Find out how many elements are in each of those arrays

Answer 23

int[][] my2DArray = new int[5][5];

System.out.println(my2DArray.length); //prints 5

System.out.println(my2DArray[0].length); // prints 4

Question 24

//use a nested for loop to print the value of the indeces?

Answer 24

for(int row = 0; row < array.length; row++){
for( int col = 0; col < array[row].length; col++){
System.out.print(array[row][col] + “ “);
}
System.out.println();
}

Question 25

//create and initialize a 2D array with a length of 2 and col length 3

//use values 1-12

Answer 25

int[][] array = {
{1, 2, 3 },
{4, 5, 6 },
{7, 8, 9 },
{10,11,12}};