Computer Science 252
Problem Solving with Java
Spring 2015, The College of Saint Rose
Matrix2D BlueJ Project
Click here to download a BlueJ project for Matrix2D.
Matrix2D Source Code
The Java source code for Matrix2D is below. Click on a file name to download it.
/*
* Example Matrix2D
*
* A class representing a 2D square matrix with some methods to manipulate
* such matrices.
*
* Jim Teresco, The College of Saint Rose, CSC 252, Fall 2013
*
* $Id: Matrix2D.java 2268 2013-11-30 22:37:49Z terescoj $
*/
import java.util.Random;
public class Matrix2D {
// the actual matrix data storage, space to be allocated by the constructor
private double [][] data;
// a basic constructor to allocate but not otherwise initialize a matrix, so
// by the rules of Java, all entries are initially 0.0.
public Matrix2D(int size) {
data = new double[size][size];
}
// initialize the entries randomly within a range
public void randomInit(double low, double high) {
Random r = new Random();
for (int row = 0; row < data.length; row++) {
for (int col = 0; col < data.length; col++) {
data[row][col] = r.nextDouble() * (high-low) + low;
}
}
}
// make this the identity matrix
public void setToIdentity() {
for (int row = 0; row < data.length; row++) {
for (int col = 0; col < data.length; col++) {
if (row == col) {
data[row][col] = 1.0;
}
else {
data[row][col] = 0.0;
}
}
}
}
// element mutator, will throw an exception of the row or column is not
// within the correct range.
public void set(int row, int col, double value)
throws Matrix2DIndexOutOfBoundsException {
if (row < 0 || row >= data.length) {
throw new Matrix2DIndexOutOfBoundsException("Row", row, data.length);
}
if (col < 0 || col >= data.length) {
throw new Matrix2DIndexOutOfBoundsException("Column", col, data.length);
}
data[row][col] = value;
}
// element accessor, again will throw an exception if bad values are passed for
// row/col.
public double get(int row, int col)
throws Matrix2DIndexOutOfBoundsException {
if (row < 0 || row >= data.length) {
throw new Matrix2DIndexOutOfBoundsException("Row", row, data.length);
}
if (col < 0 || col >= data.length) {
throw new Matrix2DIndexOutOfBoundsException("Column", col, data.length);
}
return data[row][col];
}
// compare two matrices for equality -- must be the same size then elementwise equal.
// note that we must take a parameter of type Object to override the builtin equals method.
public boolean equals(Object other) {
Matrix2D o = (Matrix2D) other;
if (data.length != o.data.length) return false;
for (int row = 0; row < data.length; row++) {
for (int col = 0; col < data.length; col++) {
if (data[row][col] != o.data[row][col]) return false;
}
}
return true;
}
// print the matrix in a nice format
public String toString() {
// use a StringBuffer to build up an answer more efficiently
StringBuffer sb = new StringBuffer();
for (int row = 0; row < data.length; row++) {
for (int col = 0; col < data.length; col++) {
sb.append(data[row][col]);
if (col != data.length-1) sb.append(" ");
}
sb.append("\n");
}
return sb.toString();
}
// nondestructive matrix-matrix add, which will throw an exception
// if the sizes do not match up (making the addition impossible).
// if all is well, we do an elementwise addition to create and return
// a brand new Matrix2D object that contains the sum of this and other.
public Matrix2D add(Matrix2D other) throws Matrix2DSizeMismatchException {
if (data.length != other.data.length) {
throw new Matrix2DSizeMismatchException(data.length, other.data.length);
}
Matrix2D result = new Matrix2D(data.length);
for (int row = 0; row < data.length; row++) {
for (int col = 0; col < data.length; col++) {
result.data[row][col] = data[row][col] + other.data[row][col];
}
}
return result;
}
// a main method that tries out some of the matrix operations here
public static void main(String[] args) throws Matrix2DSizeMismatchException,
Matrix2DIndexOutOfBoundsException {
Matrix2D a = new Matrix2D(4);
System.out.println("Uninitialized 4x4 matrix a");
System.out.println(a);
a.randomInit(0, 10);
System.out.println("4x4 matrix a after random initialization 0-10");
System.out.println(a);
// set a value in a
try {
a.set(2, 2, 0);
}
catch (Exception e) {
System.err.println(e);
}
System.out.println("4x4 matrix a after a[2][2] is set to 0");
System.out.println(a);
// try to get a value out of range
try {
double x = a.get(7, 2);
}
catch (Exception e) {
System.err.println(e);
}
Matrix2D ident = new Matrix2D(3);
ident.setToIdentity();
System.out.println("3x3 identity matrix");
System.out.println(ident);
System.out.println("Checking if a.equals(a): " + a.equals(a));
System.out.println("Checking if a.equals(ident): " + a.equals(ident));
Matrix2D b = new Matrix2D(4);
b.randomInit(-100, 100);
System.out.println("4x4 matrix b after random initialization -100 to 100");
System.out.println(b);
Matrix2D c = a.add(b);
System.out.println("4x4 matrix c=a+b");
System.out.println(c);
// finally, we'll try a mismatched size add and not catch the exception
Matrix2D d = c.add(ident);
}
}
/**
* An exception to indicate that two Matrix2D objects are not the same size when
* that is required.
*
* @author Jim Teresco
*
* $Id: Matrix2DSizeMismatchException.java 2268 2013-11-30 22:37:49Z terescoj $
*/
public class Matrix2DSizeMismatchException extends Exception
{
public Matrix2DSizeMismatchException(int size1, int size2) {
super("Matrix2D size mismatch: " + size1 + "!=" + size2);
}
}
/**
* An exception to be thrown by Matrix2D methods when a row or column
* index is specified out of range.
*
* @author Jim Teresco
*
* $Id: Matrix2DIndexOutOfBoundsException.java 2268 2013-11-30 22:37:49Z terescoj $
*/
public class Matrix2DIndexOutOfBoundsException extends Exception
{
public Matrix2DIndexOutOfBoundsException(String rowCol, int number, int size) {
super("Matrix2D " + rowCol + " " + number + " must be in range 0-" + (size-1));
}
}