Having Problems with Hashmap

Question

Hi, I'm currently creating a sparsematrix for my assignment using a hash map however i've come across a problem with how i can set an element and returning using key objects
My setElement method is
public void setElement(int nrow, int ncol, float value) throws
MatrixException {
data.put(new SparseNode(nrow,ncol), value);
and my get element is
public float getElement(int row, int col) throws MatrixException {
SparseNode node = new SparseNode(row, col);
          if (!data.containsKey(node)) {
          return 0;
return (Float) data.get(node);
where data is the map and node would be the key. The problem comes when i set the value where i give a key and this is set into the hashmap. unfortunatly the key is lost when the method exits so using the getElement method by creating a sparsenode with same characteristics as the original key won't work simply because it's not the original key. Is there another way to get around this? or some way to store the key.

Answer 1

ok well i changed to to not include the SparseNode. Now it works but very very slow. I also noticed another post with a user with the same problem but it didn't really explain how to fix it properly. Any suggestions to make this code faster?
import java.io.*;
import java.util.*;
public class SparseMatrix implements Matrix{
    private HashMap data; // non zero elements
     private int rows;
     private int columns;
    public SparseMatrix(int row, int columns) {
        data = new HashMap(row*columns);
        this.rows=row;
        this.columns=columns;
    public float getElement(int row, int col) throws MatrixException {
            if (row < 0 || col < 0 || row > this.getNumRows() || col > this.getNumCols()) {
            throw new MatrixException("Row or Column Number Beyond Dimension");
                 if (!data.containsKey((row*this.getNumCols()+col))) {
                    return 0;
        return (Float) data.get((row*this.getNumCols()+col));
    public void setElement(int nrow, int ncol, float value) throws MatrixException {
//        if (row > this.row || col > this.col) {
//           throw new MatrixException("Matrix index out of range");
        data.put((nrow*this.getNumCols()+ncol), new Float(value));
    public boolean isZero() {
        return data.isEmpty();
    // return the total number of rows in the matrix
   public int getNumRows(){
        return rows;
   // return the total number of rows in the matrix
   public int getNumCols(){
        return this.columns;
   // transpose matrix and return result as new matrix
    public Matrix transpose() {
        SparseMatrix a = new SparseMatrix(this.getNumCols(), this.getNumRows());
        for (int i =1 ; i<=this.getNumRows();i++) {
            for (int j = 1;j<=this.getNumCols();j++){
                  float value = getElement(i,j);
                 a.setElement(j, i, value );
        return a;
    * Subtracts a matrix to the current matrix and returns result as new matrix
    * @param a The Matrix to be subtracted
    * @return Returns the new matrix
   public Matrix subtract(Matrix a) throws MatrixException{
             if (this.getNumRows() != a.getNumRows() || this.getNumCols() != a.getNumCols())
                throw new MatrixException("Subtraction Cannot be Done due to Matrix Dimension MisMatch");
            if (a.isZero())
                return this;
                SparseMatrix ResultMatrix = new SparseMatrix(this.getNumRows(), this.getNumCols());
        for (int i = 1; i <= rows; i++) {
            for (int j = 1; j <= columns; j++) {          
                 float value = a.getElement(i,j);
                 float result = this.getElement(i,j) - value;
                 if (result < 0 || result > 0) {
                     ResultMatrix.setElement(i,j,result);
             return ResultMatrix;
    // add matrix and return result as new matrix
    public Matrix add(Matrix a) throws MatrixException {
            if (this.getNumRows()!= a.getNumRows() || this.getNumCols()!= a.getNumCols())
            throw new MatrixException("Addition Cannot be Done due to Matrix Dimension MisMatch");
        if (this.isZero())
            return a;
        if (a.isZero())
            return this;
            SparseMatrix ResultMatrix = new SparseMatrix(this.getNumRows(), this.getNumCols());
        for (int i = 1; i <= rows; i++) {
            for (int j = 1; j <= columns; j++) {          
                 float value = a.getElement(i,j);
                 float result = this.getElement(i,j) + value;
                 if (result < 0 || result > 0) {
                     ResultMatrix.setElement(i,j,result);
             return ResultMatrix;
// multiply matrix and return result as new matrix
     public Matrix multiply(Matrix a) throws MatrixException {
                          if (this.getNumCols() != a.getNumRows())
            throw new MatrixException("Multiplication Cannot be Done due to Matrix Dimension MisMatch");
        if (this.isZero() || a.isZero())
            SparseMatrix Temp = new SparseMatrix(this.getNumRows(), a.getNumCols());
            return Temp;
         SparseMatrix ResultMatrix = new SparseMatrix(this.getNumRows(), this.getNumCols());
          for(int i=1;i<=this.getNumRows();i++)
               for(int j=1;j<=a.getNumCols();j++)
                              float Result =0;
                              for(int k=1;k<a.getNumCols();k++)
                                   Result = Result + this.getElement(i,k)*a.getElement(k,j);
                              ResultMatrix.setElement(i,j,Result);
          return ResultMatrix;
     // print matrix in the format:
   // a11 a12 ... a1m
   // an1 an2 ... anm
    public void print(PrintStream out) {
         //System.out.println(data.toString() +"\n=====================");
        for (int i = 1; i <= this.getNumRows(); i++) {
            for (int j = 1; j <= this.getNumCols(); j++) {
                float aData = this.getElement(i, j);
                out.print(" " + aData + "");
            out.println();
}