Below is some code that is currently working (with a class and interface, which are seperated and labeled), but I am not sure if it is immutable. If it is, can someone explain to me why or, if not, can someone show me how to make it immutable? Thanks!

//Copyable Code:

Matrix.java

public interface Matrix { /** * Returns the element at particular point in the matrix. * * @param y * y position * @param x * x position * @return element */ public double getElement(int y, int x);

/** * Returns the number of rows in the matrix. * * @return rows */ public int getRows();

/** * Returns the number of columns in the matrix. * * @return columns */ public int getColumns();

/** * Returns this matrix scaled by a factor. That is, computes kA where k is a * constant and A is a matrix (this object). * * @param scalar * scalar * @return matrix */ public Matrix scale(int scalar);

/** * Returns this matrix added with another matrix. That is, computes A+B * where A and B are matrices (this object, and another respectively). * * @param other * addend * @return matrix * @throws RuntimeException * if matrices do not have matching dimensions. */ public Matrix plus(Matrix other);

/** * Returns this matrix subtracted by another matrix. That is, computes A-B * where A and B are matrices (this object, and another respectively). * * @param other * subtrahend * @return matrix * @throws RuntimeException * if matrices do not have matching dimensions. */ public Matrix minus(Matrix other);

/** * Returns true if this matrix matches another matrix. * * @param other * another matrix * @return equality */ @Override public boolean equals(Object other);

/** * Returns a string representation of this matrix. A new line character will * separate each row, while a space will separate each column. * * @return string representation */ @Override public String toString(); }

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ser222_01_02_hw02_base.java

public class ser222_01_02_hw02_base implements Matrix { private double[][] newMatrix; private int rowvalue = 0; private int columnvalue = 0;

public ser222_01_02_hw02_base(double[][] matrix) { if (matrix.length == 0) { rowvalue = 0; columnvalue = 0; } else { rowvalue = matrix.length; columnvalue = matrix[0].length;

} newMatrix = new double[rowvalue][columnvalue]; newMatrix = matrix; }

public ser222_01_02_hw02_base(int x, int y) { rowvalue = x; columnvalue = y; newMatrix = new double[x][y]; }

public double[][] getMatrix() { return newMatrix; }

@Override public double getElement(int y, int x) { // TODO Auto-generated method stub return newMatrix[y][x]; }

@Override public int getRows() { // TODO Auto-generated method stub return rowvalue; }

@Override public int getColumns() { // TODO Auto-generated method stub return columnvalue; }

@Override public Matrix scale(int scalar) { // TODO Auto-generated method stub double newval = 0; int i, j; ser222_01_02_hw02_base mat1 = new ser222_01_02_hw02_base(getRows(), getColumns()); for (i = 0; i < rowvalue; i++) { for (j = 0; j < columnvalue; j++) { newval = (getElement(i, j) * scalar); mat1.setElement(i, j, newval); } } return mat1; }

@Override public Matrix plus(Matrix other) { // TODO Auto-generated method stub double sum = 0; int i, j; if ((getRows() == other.getRows()) && (getColumns() == other.getColumns())) { ser222_01_02_hw02_base mat2 = new ser222_01_02_hw02_base(other.getRows(), getColumns()); for (i = 0; i < other.getRows(); i++) { for (j = 0; j < other.getColumns(); j++) { sum = (getElement(i, j) + other.getElement(i, j)); mat2.setElement(i, j, sum); }

} return mat2; } else return new ser222_01_02_hw02_base(0, 0); }

@Override public Matrix minus(Matrix other) { // TODO Auto-generated method stub double diff = 0; int i, j; if ((getRows() == other.getRows()) && (getColumns() == other.getColumns())) { ser222_01_02_hw02_base mat3 = new ser222_01_02_hw02_base(other.getRows(), getColumns()); for (i = 0; i < other.getRows(); i++) { for (j = 0; j < other.getColumns(); j++) { diff = (getElement(i, j) - other.getElement(i, j)); mat3.setElement(i, j, diff); } } return mat3; } else return new ser222_01_02_hw02_base(0, 0); }

public void setElement(int i, int j, double val) { newMatrix[i][j] = val; }

public boolean equals(Object other) { if (other == this) { return true; } else return false; }

public String toString() { StringBuffer sb = new StringBuffer("["); for (int i = 0; i < rowvalue; i++) { sb.append("["); for (int j = 0; j < columnvalue; j++) sb.append(" " + newMatrix[i][j] + " "); sb.append("]"); } return sb + "]"; }

public static void main(String[] args) { double[][] data1 = new double[0][0]; double[][] data2 = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } }; double[][] data3 = { { 1, 4, 7 }, { 2, 5, 8 }, { 3, 6, 9 } };

ser222_01_02_hw02_base m1 = new ser222_01_02_hw02_base(data1); ser222_01_02_hw02_base m2 = new ser222_01_02_hw02_base(data2); ser222_01_02_hw02_base m3 = new ser222_01_02_hw02_base(data3);

System.out.println("m1 --> Rows: " + m1.getRows() + " Columns: " + m1.getColumns()); System.out.println("m2 --> Rows: " + m2.getRows() + " Columns: " + m2.getColumns()); System.out.println("m3 --> Rows: " + m3.getRows() + " Columns: " + m3.getColumns());

// check for reference issues System.out.println("m2 --> " + m2); data2[1][1] = 101; System.out.println("m2 --> " + m2);

// test equals System.out.println("m2==null: " + m2.equals(null)); // false System.out.println("m3==\"MATRIX\": " + m2.equals("MATRIX")); // false System.out.println("m2==m1: " + m2.equals(m1)); // false System.out.println("m2==m2: " + m2.equals(m2)); // true System.out.println("m2==m3: " + m2.equals(m3)); // false

// test operations (valid) System.out.println("2 * m2: " + m2.scale(2)); System.out.println("m2 + m3: " + m2.plus(m3)); System.out.println("m2 - m3: " + m2.minus(m3)); } }