Question

Test all of the methods in the code below:

Instantiate several Matrix objects of different sizes.

Make a Matrix copy from an excisting Matrix

Test the equals method to show one matrix being equal and one matrix not being equal

display 2 matrices using a toString method

display a mtrix object before and after multiplying by a scalar after

display a matrix object before and after multiplying by 0

test the matrix by matrix multiplication with at least 3 different matrix objects that test different outcomes of the method including the exception

Source Code:

public class Matrix {
    private int rows, columns;
    private int[][] data;

    public Matrix(int r, int c) {
        data = new int[r][c];
        rows = r;
        columns = c;
    }

    public Matrix copyMatrix() {
        Matrix m = new Matrix(rows, columns);
        for(int i = 0; i < rows; i++)
            for(int j = 0; j < columns; j++)
                m.data[i][j] = data[i][j];

        return m;
    }

    public boolean equals(Matrix m) {
        if(rows == m.rows && columns == m.columns) {
            for(int i = 0; i < rows; i++) {
                for(int j = 0; j < columns; j++) {
                    if(m.data[i][j] != data[i][j])
                        return false;
                }
            }
            return true;
        }
        else
            return false;
    }

    public String toString() {
        String s = "";
        for(int i = 0; i < rows; i++) {
            for(int j = 0; j < columns; j++) {
                s += String.format("%5d ", data[i][j]);
            }
            s += "\n";
        }

        return s;
    }

    public void scalarMultiply(int k) {
        for(int i = 0; i < rows; i++)
            for(int j = 0; j < columns; j++)
                data[i][j] *= k;
    }


    public Matrix multiply(Matrix m) {
        if(columns != m.rows) //can't perform multiplication
            return null;

        Matrix A = new Matrix(rows, m.columns);
        for(int i = 0; i < rows; i++) {
            for(int j = 0; j < m.columns; j++) {
                for(int k = 0; k < columns; k++)
                    A.data[i][j] += data[i][k] * m.data[k][j];
            }
        }

        return A;
    }

    public void set(int r, int c, int val) {
        if(r >= 0 && r < rows && c >= 0 && c < columns)
            data[r][c] = val;
    }
}

Answer 1

TestMain.java

public class TestMain {
//static method which creates matrix object using two dimensional Array
   public static void createMatrixObject(Matrix matObject,int[][] X,int r,int c)
   {
       for(int i=0;i<r;i++)
           for(int j=0;j<c;j++)
               matObject.set(i, j, X[i][j]);
   }
  
   public static void main(String[] args) {
   //initialize various two dimensional Arrays  
   int[][] A= {{4,3,2},{5,3,1},{3,7,9}};
   int[][] B= { {2,5},{6,8}};
   int[][] C= { {8,9,7},{4,5,6},{1,5,3}};
   int[][] D= { {1,0,0},{0,1,0},{0,0,1}};
   int[][] E= { {5,2},{6,3},{2,7}};
  
//creating Matrix objects
   Matrix matObjA = new Matrix(3,3);
   createMatrixObject(matObjA,A,3,3);
   Matrix matObjB = new Matrix(2,2);
   createMatrixObject(matObjB,B,2,2);
   Matrix matObjC = new Matrix(3,3);
   createMatrixObject(matObjC,C,3,3);
   Matrix matObjD = new Matrix(3,3);
   createMatrixObject(matObjD,D,3,3);
   Matrix matObjE = new Matrix(3,2);
   createMatrixObject(matObjE,E,3,2);
  
   //copying one matrix object into another
   System.out.println("\n Copy Matrix A into another Matrix :");
   Matrix matACopy = matObjA.copyMatrix();
  
   //comapring two matrix objects
   System.out.println("\n Comparing Matrices matObjA and matACopy :"+matObjA.equals(matACopy));
   System.out.println("\n Comapring Matrices matObjA and matObjC :"+matObjA.equals(matObjC));
  
   //displaying two matrix object using toString() method
   System.out.println("\n Displaying Matrix A:\n"+matObjA.toString());
   System.out.println("\n Displaying Matrix E:\n"+matObjE.toString());
  
   //multiplying matrix object with scalar 10
   System.out.println("\n Displaying matObjB before multiplying with a scalar :\n"+matObjB.toString());
   matObjB.scalarMultiply(10);
   System.out.println("\n Displaying matObjB after multiplying with a scalar 10 :\n"+matObjB.toString());
     
   //multiplying matrix object with scalar 0
   System.out.println("\n Displaying matObjE before multiplying with a scalar :\n"+matObjE.toString());
   matObjE.scalarMultiply(0);
   System.out.println("\n Displaying matObjE after multiplying with a scalar 0 :\n"+matObjE.toString());
  
   //multiplying matrix object with another matrix object
   Matrix resMatObj=matObjA.multiply(matObjB);
   System.out.println("\n Multiplying matrix objects A and B :");
   if(resMatObj==null)
       System.out.println("\n Matix multiplication not possible");
   resMatObj=matObjA.multiply(matObjC);
   if(resMatObj!=null)
       System.out.println("\n Multiplying matrix objects A and C :\n"+resMatObj.toString());
   resMatObj=matObjC.multiply(matObjD);
   if(resMatObj!=null)
       System.out.println("\n Multiplying matrix objects C and D :\n"+resMatObj.toString());
   }
}

OUTPUT :