Implementing Matrix interface to handle 2D array as object

[R L Miller]

   I am attempting to implement an interface named Matrix and then perform various functions on the new Matrix objects. I cannot seemed to get passed go for this (college) assignment.  When I initiate a new Matrix object and pass in a 2D array, I lose the ability to access any of the indexes in the array. I know it cannot be this difficult to implement. I haven't really accomplished anything because I cannot get go far without the ability to access the elements in the arrays. Can anyone explain how to avoid this? I can find many implementations of interfaces but can't find any that convert an array to an object and then modify the contents. I have attached the interface, as well as my (lack) of code. I have essentially been stuck between lines 2-9 because without the ability to access elements, there is no point in writing anything further. Any help would be great.

public class TMatrix implements Matrix {
    Matrix matrix;
    TMatrix(int[][] m){
        matrix = new TMatrix(m);
        
    }
    public int getElement(int y, int x){
        return matrix[y][x];
    }

    public int getRows();
   
    public int getColumns();
            
    public Matrix scale(int scalar);

    public Matrix plus(Matrix other);

    public Matrix minus(Matrix other);

    @Override
    public boolean equals(Object other);
 
    @Override
    public String toString();
}



public interface Matrix {
    
    public int getElement(int y, int x);

    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();
}

[Jeanne Boyarsky]

Why are you storing a Matrix variable rather than the original 2D array?

 Matrix matrix;

[R L Miller]

I am not sure honestly, I attempted to store a 2D array but then I have some methods below that require a Matrix return type, then I tried to change the return types to int[][] and received an error that I am no longer implementing Matrix. I could have written this program without the interface in less than 10 minutes and I have been spending hours trying to utilize this interface to no avail. This makes me think I am missing something simple and obvious.

[Jeanne Boyarsky]

Your instinct to store to the 2D array was correct. Try to make just this code compile first. Then write hash code/equals/toString. Then write the other methods. That will give you a stable base to build up form.

public class TMatrix i{

    TMatrix(int[][] m){

         
    }
    public int getElement(int y, int x){
        return matrix[y][x];
    }
 
    public int getRows() {}
    
    public int getColumns() {}
             

}

[Campbell Ritchie]

Jeanne Boyarsky wrote:. . . write hash code/equals/toString.  . . .

But go through the Arrays class before you do; you may find some useful information there which makes writing those methods much much easier.