Chapter 8

public class Inherit {

	abstract class Stone {
		protected float weight = 13;
		protected int   value  = 4;
		abstract public String toString();
	}

	class Aggregate {
		protected int numKind;
	}

	class Granite extends Aggregate {
		Granite() {
			weight = 25; numKind = 7;
		}
		public String toString() {
			return "Granite: weight=" 
			   + weight + " value=" 
			   + value  + " numKind="
			   + numKind;
		}
	}

	Inherit() {
		Granite g = new Granite();
		System.out.println(g);
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	abstract class Figure {
		void display() {
			System.out.println("Figure");
		}
	}

	class Line extends Figure {
		void display() {
			System.out.println("Line");
		}
	}

	void tryme(Figure f) {
		f.display();
	}

	Inherit() {
		Figure f = new Line();
		tryme(f);
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	abstract class Figure {
		void display() {
			System.out.println("Figure");
		}
	}

	abstract class Rectangle extends Figure {
	}

	class Box extends Rectangle {
		void display() {
			System.out.println("Rectangle");
		}
	}

	Inherit() {
		Figure f = (Figure) new Box();
		f.display();
		Rectangle r = (Rectangle) f;
		r.display();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	class Figure {
		Figure() {
			System.out.println("Figure");
		}
	}

	class Rectangle extends Figure {
		void display() {
			System.out.println("Rectangle");
		}
	}

	class Box extends Rectangle {
		void display() {
			System.out.println("Box");
		}
	}

	Inherit() {
		Figure f = new Figure();
		Rectangle r = new Rectangle();
		r.display();
		Box b = new Box();
		b.display();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	class Figure {
		void display() {
			System.out.println("Figure");
		}
	}

	class Rectangle extends Figure {
		void display() {
			System.out.println("Rectangle");
		}
	}

	class Box extends Figure {
		void display() {
			System.out.println("Box");
		}
	}

	Inherit() {
		Figure f = new Figure();
		f.display();
		f = new Rectangle();
		f.display();
		f = new Box();
		f.display();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	class Figure {
		void display() {
			System.out.println("Figure");
		}
	}

	class Rectangle extends Figure {
		void display() {
			System.out.println("Rectangle");
		}
	}

	class Box extends Figure {
		void display() {
			System.out.println("Box");
		}
	}

	Inherit() {
		Figure f = new Figure();
		Rectangle r = new Rectangle();
		Box b = new Box();
		f.display();
		f = r;
		f.display();
		f = b;
		f.display();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	class Figure {
		void display() {
			System.out.println("Figure");
		}
	}

	class Rectangle extends Figure {
		void display() {
			System.out.println("Rectangle");
		}
		void display(String s) {
			System.out.println(s);
		}
	}

	class Box extends Figure {
		void display() {
			System.out.println("Box");
		}
		void display(String s) {
			System.out.println("This is printed: " + s);
		}
	}

	Inherit() {
		Figure f = new Figure();
		Rectangle r = new Rectangle();
		Box b = new Box();
		f.display();
		f = r;
		f.display("one");
		f = b;
		f.display("two");
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	class Figure {
		void display() {
			System.out.println("Figure");
		}
	}

	class Rectangle extends Figure {
		final void display() {
			System.out.println("Rectangle");
		}
	}

	class Box extends Rectangle {
		void display() {
			System.out.println("Box");
		}
	}

	Inherit() {
		Figure f = new Figure();
		Rectangle r = new Rectangle();
		Box b = new Box();
		f.display();
		r.display();
		b.display();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	class Figure {
		void display() {
			System.out.println("Figure");
		}
	}

	class Rectangle extends Figure {
		void display() {
			System.out.println("Rectangle");
		}
	}

	class Box extends Rectangle {
		void display() {
			System.out.println("Box");
		}
	}

	Inherit() {
		Figure f = new Figure();
		Rectangle r = new Rectangle();
		Box b = new Box();
		f.display();
		f = r;
		((Figure) f).display();
		f = (Figure) b;
		f.display();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

public class Inherit {

	abstract class Speaker {
		abstract public void speak();
	}

	class Cat extends Speaker {
		public void speak() {
			System.out.println("Woof!");
		}
	}

	class Dog extends Speaker {
		public void speak() {
			System.out.println("Meow!");
		}
	}

	Inherit() {
		Speaker d = new Dog();
		Speaker c = new Cat();
		d.speak();
		c.speak();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

1. If a class is declared to be abstract then every method in the class is abstract and must be overridden
2. If a class is declared to be abstract then some methods in the class may have their bodies omitted
3. If a class is declared to be abstract then all methods in the class must have their bodies omitted
4. If a class is declared to be abstract then all the instance variables must be overridden when a concrete class is derived from the abstract base class

1. Java upcasts automatically, but you must explicitly downcast
2. Java downcasts automatically, but you must explicitly upcast
3. Java expects the user to explicitly upcast and downcast
4. Java will both upcast and downcast automatically
5. The rules for upcasting and downcasting depend upon whether classes are declared public, protected, or private