implementing an interface java newbie

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?

You cannot overload operators in Java

Esailija
– Esailija

2013-01-03 20:22:33 +00:00
Commented Jan 3, 2013 at 20:22 — Esailija
– Esailija, Commented Jan 3, 2013 at 20:22
How do you add matrices of different dimensions?

SJuan76
– SJuan76

2013-01-03 20:27:48 +00:00
Commented Jan 3, 2013 at 20:27 — SJuan76
– SJuan76, Commented Jan 3, 2013 at 20:27

stacker · Accepted Answer · 2013-01-03 20:28:01Z

6

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.

answered Jan 3, 2013 at 20:28

stacker

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1 Comment

Mel Nicholson Over a year ago

You can also throw new IllegalArgumentException(); if the number of columns don't match.

Community · Accepted Answer · 2020-06-20 09:12:55Z

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); }

mprivat · Accepted Answer · 2013-01-03 20:30:41Z

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:

expand your matrix
copy the b rows into the newly expanded matrix
return the new number of rows

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

Kyle · Accepted Answer · 2013-01-03 20:31:56Z

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.

BevynQ · Accepted Answer · 2013-01-03 20:36:41Z

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 } ... }

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