CODEWITHSUNDEEP
java
frazman
frazman

Reputation: 33243

implementing an interface java newbie

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?

Upvotes: 2

Views: 993

Answers (5)

Marcin Szymczak
Marcin Szymczak

Reputation: 11433

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);
}

Upvotes: 1

BevynQ
BevynQ

Reputation: 8269

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
    }

    ...

}

Upvotes: 0

Kyle
Kyle

Reputation: 4298

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.

Upvotes: 0

mprivat
mprivat

Reputation: 21902

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.

Upvotes: 0

stacker
stacker

Reputation: 68962

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.

Upvotes: 6

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