Java OCA OCP Practice Question 2542

Question

What is the result of compiling the following class? 

public class Book { 
   private int ISBN; 
   private String title, author; 
   private int pageCount; 
   public int hashCode() { 
      return ISBN; 
   } /* w w  w . java  2  s .c  om*/
   @Override public boolean equals(Object obj) { 
     if ( !(obj instanceof Book)) { 
        return false; 
     } 
     Book other = (Book) obj; 
     return this.ISBN == other.ISBN; 
   } 
// imagine getters and setters are here 
}
  • A. The code compiles.
  • B. The code does not compile because hashCode() is incorrect.
  • C. The code does not compile because equals() does not override the parent method correctly.
  • D. The code does not compile because equals() tries to refer to a private field.
  • E. The code does not compile because the ClassCastException is not handled or declared.
  • F. The code does not compile for another reason.


A.

Note

hashCode() is correct and perfectly reasonable given that equals() also checks that field.

ClassCastException is a runtime exception and therefore does not need to be handled or declared.

The override in equals() is correct.

It is common for equals() to refer to a private instance variable.

This is legal because it is within the same class, even if it is referring to a different object of the same class.




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