Java OCA OCP Practice Question 66

Question

For the following code: 

1. package abcde; 
2. //  w  w w .  j  av  a 2s  .  co  m
3. public class Bird { 
4.   protected static int referenceCount = 0; 
5.   public Bird() { referenceCount++; } 
6.   protected void fly() { /* Flap wings, etc. */ } 
7.   static int getRefCount() { return referenceCount; } 
8. } 

Which statement is true about class Bird and the following class MyClass? 

 1. package singers; 
 2. /*from  www  .j a  va 2s.  c  o m*/
 3. class MyClass extends abcde.Bird { 
 4.   MyClass() { referenceCount++; } 
 5. 
 6.   public static void main(String args[]) { 
 7.     System.out.print("Before: " + referenceCount); 
 8.     MyClass florence = new MyClass(); 
 9.     System.out.println("  After: " + referenceCount); 
10.     florence.fly(); 
11.   } 
12. }
  • A. The program will compile and execute. The output will be Before: 0 After: 2.
  • B. The program will compile and execute. The output will be Before: 0 After: 1.
  • C. Compilation of MyClass will fail at line 4 because static members cannot be overridden.
  • D. Compilation of MyClass will fail at line 10 because method fly() is protected in the superclass.
  • E. Compilation of MyClass will succeed, but an exception will be thrown at line 10, because method fly() is protected in the superclass. 


A.

Note

There is nothing wrong with MyClass.

The static referenceCount is bumped twice: once on line 4 of MyClass and once on line 5 of Bird.

The no-argument constructor of the superclass is implicitly called at the beginning of a class's constructor, unless a different superclass constructor is requested.

Because referenceCount is bumped twice and not just once, answer B is wrong.

C says that statics cannot be overridden, but no static method is being overridden on line 4.

D is wrong since protected is the access modifier you want Bird.fly() to have: you are calling Bird.fly() from a subclass in a different package.

Answer E is wrong.




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