InheriTest.java Questions

Instructions

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Program listing

// InheriTest.java
// Copyright (C) 1998-2016 Davin Pearson
// Website: http://davin.50webs.com/java-tutorials

class Animal
{
   // Properties of the class...
   public int     numberOfLegs;
   public boolean hasWings;

   // Constructor of the class...
   public Animal()
   {
      numberOfLegs = 4;
      hasWings = false;
   }

   // Methods of the class...
   public void talk()
   {
      System.out.println("Hello");
   }
}

class Bird extends Animal
{
   // Properties of the class...
   public boolean canFly;

   // Constructor of the class...
   public Bird()
   {
      super();
      numberOfLegs = 2;
      hasWings = true;
      canFly = true;
   }

   // Methods of the class...
   public void fly() {
      System.out.println("flap flap");
   }
}

class Eagle extends Bird
{
   // Properties of the class...
   private int numberOfKills;

   // Constructor of the class...
   public Eagle()
   {
      super();
      numberOfKills = 0;
   }

   // Methods of the class...
   public void attack()
   {
      numberOfKills++;
   }
}

class InheriTest
{
   // The main method is the point of entry into the program...
   public static void main(String[] args)
   {
      Animal a = new Animal();
      System.out.println(a.numberOfLegs);
      System.out.println(a.hasWings);
      a.talk();
      a.fly();

      Bird b = new Bird();
      System.out.println(b.numberOfLegs);
      System.out.println(b.hasWings);
      System.out.println(b.canFly);
      System.out.println(b.numberOfKills);
      b.talk();
      b.attack();

      Eagle e = new Eagle();
      System.out.println(e.numberOfKills);
      System.out.println(e.numberOfLegs);
      System.out.println(e.hasWings);
      e.talk();
      e.attack();
   }
}

// QUESTIONS:

// (1) Without compiling this file, use your understanding
// of inheritance to say which of the statements in this
// file will not compile and why.  Then use the compiler to
// check that your guesses were correct and comment out all
// the statements with errors in them.

// (2) For each statement that doesn't compile, comment it
// out and beside it write a brief reason why the compiler
// doesn't accept it.

// (3) NOTE: It is essential for the next question that the
// incorrect lines are commented out.

// (4) Compile and run InheriTest to see what is printed
// to the screen.

// (5) Why is the number printed out for "e.numberOfLegs"
// equal to 2 when there is no mention of ever setting the
// value for "numberOfLegs" to 2 in the Eagle class?
//
// HINT: It has something to do with "super".
// 
// (6) Add the following three lines to the main method:

//  a = b;
//  a.talk();
//  a.fly();

// If you compile the code, one of these lines gives a
// compiler error.  Which line is it and what is the reason
// for the error?
// 
// (7) Remove the lines you added from question (6) and add
// the following three lines to the main method:

//  b = a;
//  b.talk();
//  b.fly();

// If you compile the code, one of these lines gives a
// compiler error.  Which line is it and what is the reason
// for the error?
//