Homework Answers

Write a method called isIdentityMatrix which will take a two-dimensional integer

array as argument, and returns true if the array is an identity matrix, or false otherwise.

You may use the following header for this method:

static boolean isIdentityMatrix(int[][] array)

A matrix is an identity matrix if it is a square matrix, and all its elements at the left

diagonal are ones, and all other elements are zeroes.

For example, the following matrix is an identity matrix and the method should return true

if we pass it to the isIdentityMatrix matrix as two-dimensional:

1 0 0 0 0

0 1 0 0 0

0 0 1 0 0

0 0 0 1 0

0 0 0 0 1

For the following two-dimensional array, the method should return false because there

are some non-zero elements in the matrix.

1 0 0 5 0

0 1 0 2 0

0 3 1 0 0

0 0 0 1 5

0 5 0 0 1

Similarly, for the following two-dimensional array, the method should return false

because some elements at left diagonal are not ones.

1 0 0 0 0

0 0 0 0 0

0 0 0 0 0

0 0 0 1 0

0 0 0 0 1

Write a method called addMatrices which will take two matrices (two-dimensional

integer arrays) as argument, and returns the addition of these two matrices as a two-

dimensional integer array.

You may use the following header for this method:

static int[][] addMatrices(int[][] firstMatrix,

int[][] secondMatrix)

For example, if we pass the following two two-dimensional arrays to the method:

5 7 9 4 3 7 3 2 1 5

2 3 9 7 6 3 9 4 0 3

3 6 8 7 9 6 2 8 9 4

1 9 7 5 6 5 0 3 8 7

3 8 7 9 2 1 6 8 4 3

Then the method should return the following two-dimensional array:

12 10 11 5 8

5 12 13 7 9

9 8 16 16 13

6 9 10 13 13

4 14 15 13 5

2. Write a method called printArray that takes a two-dimensional integer array as

argument and prints all elements of array. The method should print each row line by line.

You may use the following header for this method:

static void printArray(int[][] array)

In the main method:

 Declare and initialize two two-dimensional arrays.

 Pass these two-dimensional arrays to addMatrices()method..

In this task, you are being asked to write methods that manipulate arrays in Java.

1. Write a method called swapFirstAndLastRow which will take a two-dimensional

integer array as argument and swap all the values of first row and last row with each

other.

You may use the following header for this method:

static void swapFirstAndLastRow(int[][] array)

For example, if we pass the following two-dimensional array to this method:

5 7 9 4 3 1

2 4 9 7 6 5

3 6 8 7 9 4

1 9 7 5 6 3

Then the array will become:

1 9 7 5 6 3

2 4 9 7 6 5

3 6 8 7 9 4

5 7 9 4 3 1

2. Write a third method called printArray which will take a two-dimensional integer

array as argument and prints all elements of array. The method should print each row line

by line.

You may use the following header for this method:

static void printArray (int[][] array)

Take two numbers from the user as the size of rows and columns of the array and call the

methods in the following order:

 printArray()

 swapFirstAndLastRow()

 printArray