Java OCA OCP Practice Question 2872

Question

Assuming the following class has proper public getter/setter methods for all of its private fields, which of the following fields will always be null after an instance of the class is serialized and then deserialized? (Choose all that apply.). 

public class Cat implements Serializable { 
   private static final long serialUID = 1L; 
   private transient String name = "George"; 
   private static String birthPlace = "Africa"; 
   private transient Integer age; 
   private java.util.List<Cat> friends = new java.util.ArrayList<>(); 
   private Object tail = null; 
   { age = 10;} /*w w  w . ja  v  a2 s . com*/

   public Cat() { 
      this.name = "Sophia"; 
   } 
}
  • A. name
  • B. tail
  • C. age
  • D. friends
  • E. birthPlace
  • F. The code does not compile.
  • G. The code compiles but throws an exception at runtime.


A, C.

Note

The code compiles and runs without issue, so F and G are incorrect.

Note that serialUID is not the same as serialVersionUID, although since serialVersionUID is recommended but not required, this does not pose any compilation issues.

Just be aware that serialUID will not be used by the serialization process for version control.

The name variable and age variable are both transient, which means that their values will not be saved upon serialization.

Upon deserialization, the default initializations and constructor will be skipped, and they will both be null; therefore A and C are correct.

B is incorrect because tail is not transient and could be set by a caller before being serialized.

D is also incorrect because a serialized empty array is not the same as a null pointer.

Even though these non-transient fields could be set to null, they are not guaranteed to be null after deserialization.

E is incorrect because the static value will not be serialized; it will be available on the class after deserialization.




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