public class Rectangle {
	private double w,h;
	Rectangle(double w, double h) {
		this.w = w;
		this.h = h;
	}
	Rectangle setWidth(double newW) {
		return new Rectangle(newW, h);
	}
	Rectangle setHeight(double newH) {
		return new Rectangle(w, newH);
	}
	double getWidth() {
		return w;
	}
	double getHeight() {
		return h;
	}
	void show() {
		System.out.println("Rectangle("+getWidth()+","+getHeight()+")");
	}
}



public class Square extends Rectangle {
	Square(double side) {
		super(side, side);
	}
	void show() {
		System.out.println("Square("+getWidth()+","+getHeight()+")");
	}
}


public class Main {
	public static void main(String[] args) {
		Square s = new Square( 5 );
		Rectangle r = s.setWidth( 10 );
		s.show();
		r.show();
	}
}

public class Square extends Rectangle {
	Square(double side) {
		super(side, side);
	}
	Square setSide(double newSide) {
		return new Square( newSide );
	}
	void show() {
		System.out.println("Square("+getWidth()+")");
	}
}

public class Main {
	public static void main(String[] args) {
		Square s = new Square( 5 );
		Rectangle r = s.setWidth( 10 );
		s.show();
		r.show();
		s = s.setSide( 3 );
		s.show();
	}
}

Square s  = new Square(  5  );
Square evil = s.SetWidth(  10  ); // опа!

Square s  = new Square(  5  );
Square evil = s.setSide(  10  ); // опа!

z -некоторый кортеж
Square s = new Square( 5 );
Rectangle r = s;
r.method(z);
s = r;

z -некоторый кортеж;
Square s = new Square( 5 );
Rectangle r = s;
s = r.method(z);

[color=red]s = r;[/color]

[color=red]s = r;[/color]

public class Rectangle {
	private double w,h;
	public Rectangle(double w, double h) {
		this.w = w;
		this.h = h;
	}
	public Rectangle setWidth(double newW) {
		return new Rectangle(newW, h);
	}
	public Rectangle setHeight(double newH) {
		return new Rectangle(w, newH);
	}
	public double getWidth() {
		return w;
	}
	public double getHeight() {
		return h;
	}
}



public class Square extends Rectangle {
	public Square(double side) {
		super(side, side);
	}
	public Square(Rectangle r) {
		this(r.getHeight());
	}
	public Square setSide(double newSide) {
		return new Square( newSide );
	}
	
}


public class Main {
	static void showRectangle(Rectangle r) {
		System.out.println("Rectangle("+r.getWidth()+","+r.getHeight()+")");
	}
	static void showSquare(Square s) {
		System.out.println("Square("+s.getWidth()+")");
	}
	
	public static void main(String[] args) {
		Square s = new Square( 5 );
		Rectangle r = s.setWidth( 10 );
		showRectangle(r);
		showSquare(new Square(r)); //явное преобразование вниз по иерархии
	}
}

Rectangle( 10 . 0 , 5 . 0 )
Square( 5 . 0 )