实现接口Java新手

Question

I am a newbie in java and I am trying to implement an interface.

So main class

public interface Matrix{
    //returns number of rows
    int numRows();
    //returns number of columns
    int numColumns();

    int addRows(...);
    ....
}

Now basically what I am trying to solve is lets say.. I have two matrices matrixa and matrixb of type Matrix .

I want to basically extend the matrix row wise. So if matrixa had 10 rows and matrixb has 2 rows. Then I want to return matrixa+=matrixb

(offcourse assuming that number of columns are same.)

What is the right way to do this?

Answer 1

You could add another method to your interface like:

   public interface Matrix{
             ....
           Matrix add( Matrix b );
    }

and check for the necessity to expand rows in the implementation.

Answer 2

Why You can't do exactly what You want?

Java has no operator overloading. You can not use += with your objects. It is generally believed in java world that operator overloading decreases readablility.

What You can do

However you can use methods such as addMatrix(Matrix m) .

public interface Matrix{
    int getNumberOfRows();
    int getNumberOfColumns();

    Matrix addMatrix(Matrix m);
}

Answer 3

The easy answer is: you implement an interface by reading this http://docs.oracle.com/javase/tutorial/java/IandI/usinginterface.html

I would start with java tutorials since you are a beginner. You can't instantiate an interface, an interface (typically) only contains method header definitions. The way you use interfaces is you implement them by creating a normal java class that implements code for each of the methods found in the interface.

Btw, I would highly recommend reading tutorials rather than relying on SO for questions like this.

Answer 4

I'm trying to make sense of the question. I think what you are trying to do is define:

int addRows(Matrix b);

In that method implementation, you would:

1. expand your matrix
2. copy the b rows into the newly expanded matrix
3. return the new number of rows

All of this implementation is dependent on how you implement the Matrix interface.

Answer 5

To implement an interface you create a class that implements the interface and all of it's methods.

public class MatrixImpl implements Matrix{

    private List<List<Integer>> elements = new ArrayList<List<Integer>>();
    private int rowSize;

    ...

    /** appends rows from provided matrix to this matrix */
    public Matrix addRows(Matrix b){
        List<List<Integer>> rows;
        if (b == this){
            rows = new ArrayList(b.elements);
        }else {
            rows = b.elements;
        }
        for (List<Integer> row : rows){
           if(row.size() == rowSize){
              elements.add(new ArrayList(row));
           }else{
              // do some error handling
           }
        }
        return this;// you may want to return a clone instead
    }

    ...

}