//Chapter 9 inheritance stuff crammed into here
// abstract superclass

public class Inheritance6 {
    public static void main( String[] args ) {
	//X x1 = new X();   //syntax error.  can not instantiate abstract class
	X x1;    //can have a abstract class reference variable
	Y y1 = new Y();
	W w1 = new W();

	y1.m1();
	w1.m1(); 
	y1.m2(); 
	w1.m2(); 
    }
}

//abstract class has abstract method(s)
//abstract class can not be instantiated.
//can provide some inherited methods and fields.
//use for a class type that is too "abstract" to have actual objects,
//provide some common code for subclasses and require them to implement
//certain functionality (the abstract methods)
abstract class X {
    int i=3;
    void m1() {
	System.out.println( "hello from X m1()" );
    }
    //abstract method has no body
    abstract void m2();  
}


//class that derives from an abstract class MUST implement the abstract methods
//or else be abstract itself
class Y extends X {
    void m2() {
	System.out.println( "hello from Y m2()" );
    }

}

class W extends X {
    void m2() {
	System.out.println( "hello from W m2()" );
    }

}