Initial revision

Matrices.java

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+// Andrew Coleman
+// Matrices.java
+// demonstrates the use of the Matrix class
+
+import Matrix;
+
+public class Matrices	{
+	public static void main (String[] args)	{
+		int[][] matrix1 = {{1, 1, 1}, {5, 6, 4}, {0, 2, 3}};
+		int[][] matrix2 = {{0, 0, 0}, {4, 9, 2}, {1, -2, 6}};
+		Matrix m1 = new Matrix(matrix1);
+		Matrix m2 = new Matrix(matrix2);
+		System.out.println(m1 + "\n");
+		System.out.println(m2 + "\n");
+		System.out.println("Addition:");
+		System.out.println(m1.add(m2)+"\n");
+		System.out.println("Subtraction:");
+		System.out.println(m1.subtract(m2)+"\n");
+		System.out.println("Multiplication:");
+		System.out.println(m1.multiply(m2)+"\n");
+		System.out.println("scalar multiplication (m1 * 2):");
+		System.out.println(m1.scalar_multiply(2)+"\n");
+	}
+}

Matrix.java

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+//	Andrew Coleman
+//	Matrix.java
+//	Class for using a matrix of integers
+//	and a set of algorithms to perform on the matrix
+
+public class Matrix	{
+	private int rows = 0, cols = 0;
+	private int[][] matrix;
+
+	// the standard constructor
+	public Matrix (int r, int c)	{
+		rows = r;cols = c;
+		matrix = new int[rows][cols];
+	}
+
+	// constructor to use with an array
+	public Matrix (int[][] array)	{
+		rows = array.length;
+		cols = array[0].length;
+		matrix = new int[rows][cols];
+		for (int r = 0; r < rows; r++)
+			for (int c = 0; c < cols; c++)
+				matrix[r][c] = array[r][c];
+	}
+
+	public int getRows ()	{
+		return rows;
+	}
+
+	public int getColumns ()	{
+		return cols;
+	}
+
+	public int getElement (int r, int c)	{
+		if (r <= rows && c <= cols)
+			return matrix[r][c];
+		return -999;
+	}
+
+	public Matrix setElement (int r, int c, int value)	{
+		if (r <= rows && c <= cols)
+			matrix[r][c] = value;
+		return this;
+	}
+
+	// adds the totals in a row
+	public int addRow (int r)	{
+		int result = 0;
+		for (int i = 0; i < rows; i++)
+			result += matrix[r][i];
+		return result;
+	}
+
+	// adds the totals in a column
+	public int addColumn (int c)	{
+		int result = 0;
+		for (int i = 0; i < cols; i++)
+			result += matrix[i][c];
+		return result;
+	}
+
+	// adds two matrices
+	public Matrix add (Matrix m2)	{
+		if (m2.getRows() == rows && m2.getColumns() == cols)	{
+			int[][] result = new int[rows][cols];
+			for (int r = 0; r < rows; r++)
+				for (int c = 0; c < cols; c++)
+					result[r][c] = this.getElement(r, c) + m2.getElement(r, c);
+			return new Matrix(result);
+		}
+		return this;
+	}
+
+	// subtracts two matrices
+	public Matrix subtract (Matrix m2)	{
+		if (m2.getRows() == rows && m2.getColumns() == cols)	{
+			int[][] result = new int[rows][cols];
+			for (int r = 0; r < rows; r++)
+				for (int c = 0; c < cols; c++)
+					result[r][c] = this.getElement(r, c) - m2.getElement(r, c);
+			return new Matrix(result);
+		}
+		return this;
+	}
+
+	// multiplies two matricies
+	public Matrix multiply (Matrix m2)	{
+		if (m2.getRows() == cols && rows == m2.getColumns() )	{
+			int[][] result = new int[rows][m2.getColumns()];
+			for (int r = 0; r < rows; r++)
+				for (int c = 0; c < m2.getColumns(); c++)
+					result[r][c] = this.addRow(r) + m2.addColumn(c);
+			return new Matrix(result);
+		}
+		return this;
+	}
+
+	// multiplies the current matrix by a scalar value
+	public Matrix scalar_multiply (int value)	{
+		int[][] result = new int[rows][cols];
+		for (int r = 0; r < rows; r++)
+			for (int c = 0; c < cols; c++)
+				result[r][c] = matrix[r][c] * value;
+		return new Matrix(result);
+	}
+
+	// checks equality on another matrix
+	public boolean equals(Matrix m2)	{
+		boolean result = true;
+		if (rows == m2.getRows() && cols == m2.getColumns() )
+			for (int r = 0; r < rows; r++)
+				for (int c = 0; c < cols; c++)
+					if (matrix[r][c] != m2.getElement(r, c) && result)
+						result = false;
+		return result;
+	}
+
+	// overridden toString method to give you a very pretty output
+	public String toString()	{
+		String result = "";
+		for (int r = 0; r < rows; r++)	{
+			result += " [ ";
+			for (int c = 0; c < cols; c++)
+				result += (matrix[r][c] + " ");
+			result += "]\n";
+		}
+		return result;
+	}
+}