Java OCA OCP Practice Question 2874

Question

What is the value of name after an instance of Eagle is serialized and then deserialized? 

public class Cat implements Serializable { 
   protected transient String name = "SQL"; 
   public void setName(String name) { this.name = name; } 
   public String getName() { return name; } 
   public Cat() { 
      this.name = "Ruby"; 
   } /*from   w  w w  . j  ava 2 s.c  o  m*/
} 
public class Eagle extends Cat implements Serializable { 
   { this.name = "Java"; } 

   public Eagle() { 

      this.name = "Javascript"; 
   } 
}
  • A. SQL
  • B. Ruby
  • C. Java
  • D. Javascript
  • E. null
  • F. The code does not compile.
  • G. The code compiles but throws an exception at runtime.
  • H. The value may not be known until runtime.


E.

Note

First off, even though the Cat class implements Serializable, it does not define a static serialVersionUID variable, which is recommended but not required; therefore it compiles without issue and F is incorrect.

The code also runs without issue, so G is incorrect.

The key here is that Java will call the constructor for the first non-serializable no-argument parent class during deserialization,

skipping any constructors and default initializations for serializable classes in between, including Eagle and Cat itself.

Therefore, Object() is the first constructor called.

All default initializations are skipped, so A, B, C, and D are all incorrect.

Since the name is marked transient, the deserialized value is null and E is correct.

H is also incorrect, because the caller cannot change the serialized value of name with setName(), since name is marked transient.




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