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Liskov replacement principle - How to model a square and a rectangle

Possible duplicate:
Is a square from a rectangle a violation of the Liskov Substitution Principle?

Using LSP, can anyone give me an implementation of Square and Rectangle?

I read the book "Head First Object-Oriented Analysis and Design", they said that if Sqaure inherits from Rectangle, it violated the LSP, but does not have the correct implementation.

Anyone want a try?

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5 answers

If you make the square and rectangle immutable, then you will not violate the LSP.

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public class Rectangle {
    int width;
    int height;

    public Rectangle(int w, int h) {
        width = w;
        height = h;
    }

    //getWidth(), getHeight, getArea(), etc, but no setters.
}


public Square extends Rectangle {
    public Square(int side) {
        super(side, side);
    }
}

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