2dimension matrix interface for add() and copy()

Trying to implements the interface functions. Having some issues.

1. For makeEmpty() function seems like i need to transverse the matrix but not sure what that means
2. For addition and copy function how should i do it

For the test class i havent write yet. Not very sure how to write java class

public class Matrix implements MatrixInterface{
    private int [][] matrixArray;
    private int dimension;
    
    public Matrix(int n){
        matrixArray = new int[n][n];
        dimension = n;
    }
    
    
    @Override
    public void makeEmpty(int m) {
        //check dimension - conditional statement
        if(m > dimension){
            m = dimension;
        }
       
        //transverse the matrix rows and cols
        
        //loops = 2 loops
        for(int i=0; i<=m; i++){
            for(int j=0; j<=m; j++){
                matrixArray[i][j]=0;   // matrix at i row and j col =0
            }
        }
    }

    @Override
    public boolean storeValue(int i, int j, int value) {
        for(int p=0; p<=i; p++){
            for(int q=0; q<=j; q++){
                matrixArray[p][q] = value;
            }
        }
        
        return true;
    }

    @Override
    public boolean add(MatrixInterface anotherMatrix) {
        for (int i=0; i < dimension; i++){
            for (int j=0; j < dimension; j++ ){
                
            }
        }
        return true;
    }

    @Override
    public boolean copy(MatrixInterface anotherMatrix) {
       
    }

    @Override
    public String toString() {
        String outputStr = "";
        for(int i=0; i<dimension; ++i){
            for(int j=0; j<dimension; ++i){
                outputStr += String.format("%4d", matrixArray[i][j]);
            }
            outputStr += "\n";
        }
        
        return outputStr;
    }
    
}

java interface

is boolean type for add() and copy() correct?

public interface MatrixInterface {
    void makeEmpty(int m);
    boolean storeValue(int i, int j, int value) ;
    
    boolean add(MatrixInterface anotherMatrix);
    boolean copy(MatrixInterface anotherMatrix);
}