Java- Interface makes use of an interface

Question

I'm studying code. I 've found these two classes. I don't understand how they are related. What does the Expression "T extends PieceType" mean, what does the T stand for?

piece.java:

public interface Piece<T extends PieceType> {

    /**
     * Returns the color.
     * @return the color
     */
    PieceColor getColor();    

    /**
     * Returns the type.
     * @return the type
     */
    T getType();
}

pieceType.java:

public interface PieceType {

    /**
     * Returns the type's base rating.
     * @return the base rating within range [0, 1000]
     */
    double getRating();
}

You need to read about Generics. Start here.

Sotirios Delimanolis
– Sotirios Delimanolis

2013-07-25 13:30:56 +00:00
Commented Jul 25, 2013 at 13:30 — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jul 25, 2013 at 13:30
After you digest that, move on to here.

Steve P.
– Steve P.

2013-07-25 13:34:31 +00:00
Commented Jul 25, 2013 at 13:34 — Steve P.
– Steve P., Commented Jul 25, 2013 at 13:34

SamJB · Accepted Answer · 2013-07-25 13:39:03Z

4

As mentioned, it means that the type, T, that you pass into Piece must extend PieceType.

Here we have an interface that extends PieceType:

public interface NewPiece extends PieceType {
    ...
}

You would then instantiate a Piece object by doing this:

Piece<NewPiece> aPiece = new SomeImplementationOfPiece<NewPiece>();

Because NewPiece extends PieceType as given in your definition:

public interface Piece<T extends PieceType> { ... }

answered Jul 25, 2013 at 13:39

SamJB

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Comments

arshajii · Accepted Answer · 2013-07-25 13:30:57Z

3

The interface Piece is generic, and its single type parameter T must implement PieceType, as indicated by T extends PieceType. It might behoove you to read further into generics; the linked lesson should be a good start.

answered Jul 25, 2013 at 13:30

arshajii

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