//
// contrived example of using inheritance and polymorphism
// 

import java.util.* ;

//
// define a hierarchy of classes to hold integers, with each class
//              providing the following methods:
//
//      printNum prints the number, plus "is prime" for primes
//      printSquare prints the number squared
//      printSquareRoot prints the number's square root if >= 0,,
//              an error message if < 0
//

//
// base class gives "default" behavior
//

class NumObj {

        int num ;

        NumObj(int n) {
                num = n ;
        }

        void printNum() {
                System.out.println(num) ;
        }

        void printSquare() {
                System.out.println(num + " squared is " + num*num) ;
        }

        void printSquareRoot() {
                System.out.println("unable to find square root of " +
                        num) ;
        }
}

//
// class for numbers >= 0 overrides some default behavior
//

class NonNegNumObj extends NumObj {

        NonNegNumObj(int n) {
                super(n) ;
        }

        // 
        void printSquareRoot() {
                System.out.println("square root of " + num + " is " +
                        Math.sqrt(num)) ;
        }

}

//
// class for prime numbers (which are >= 0) overrides additional
//      default behavior
//

class PrimeNumObj extends NonNegNumObj {

        PrimeNumObj(int n) {
                super(n) ;
        }

        void printNum() {
                System.out.println(num + " is prime") ;
        }
}

//
// main method showing use of NumObj and its subclasses
//

public class NumObjs {

        public static void main(String[] args) {

                // build a vector containing some NumObjs (of
                //      different subtypes)

                Vector v = new Vector() ;
                v.addElement(new NumObj(-2)) ;
                v.addElement(new NonNegNumObj(0)) ;
                v.addElement(new PrimeNumObj(2)) ;
                v.addElement(new PrimeNumObj(3)) ;
                v.addElement(new NonNegNumObj(4)) ;

                // invoke NumObj methods on each element

                Enumeration e = v.elements() ;
                while (e.hasMoreElements()) {
                        NumObj o = (NumObj) e.nextElement() ;
                        o.printNum() ;
                        o.printSquare() ;
                        o.printSquareRoot() ;
                }
        }
}