Hello everyone, my name is Konstantin. I am developing in Java at Tinkoff.ru and love SOLID. In this article, we will formulate the Lisk substitution principle, show its connection with the Open-Closed principle, learn how to properly form the inheritance hierarchy, and answer the philosophical question of whether a square is a rectangle.

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void drawShape(Shape shape) {
   if (shape instanceof Square) {
       drawSquare((Square) shape);
   } else {
       drawCircle((Circle) shape);
   }
}

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public class Rectangle {
    private int width;
    private int height;

    public int getWidth() {
        return width;
    }

    public void setWidth(int width) {
        this.width = width;
    }

    public int getHeight() {
        return height;
    }

    public void setHeight(int height) {
        this.height = height;
    }

    public int perimeter() {
        return 2 * height + 2 * width;
    }
}

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    @Override
    public void setWidth(int width) {
        super.setWidth(width);
        super.setHeight(width);
    }

    @Override
    public void setHeight(int height) {
        super.setHeight(height);
        super.setWidth(height);
    } 

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public class RectangleTest {

    @Test
    public void perimeter() {
        Rectangle rectangle = new Rectangle();
        rectangle.setHeight(5);
        rectangle.setWidth(7);

        int result = rectangle.perimeter();

        assertEquals(24, result);
    }

} 

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public class RectangleTest {

    @Test
    public void perimeter() {
        Rectangle rectangle = initRectangle();
        rectangle.setHeight(5);
        rectangle.setWidth(7);

        int result = rectangle.perimeter();

        assertEquals(24, result);
    }

    protected Rectangle initRectangle() {
        return new Rectangle();
    }

}

public class SquareTest extends RectangleTest {

    @Override
    protected Rectangle initRectangle() {
        return new Square();
    }

}

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