Java Serialization with Aggregation (HAS-A Relationship)

If a class has a reference to another class, all the references must be Serializable otherwise serialization process will not be performed. In such case, NotSerializableException is thrown at runtime.

Address.java

class Address { 

     String hNo,city,state; 

     public Address(String hNo, String city) { 

           this.hNo=hNo; 

           this.city=city; 

     } 

}

Employee.java

import java.io.Serializable; 

public class Employee implements Serializable { 

     int id; 

     String name; 

     Address address;//HAS-A 

     public Employee(int id, String name) { 

           this.id = id; 

           this.name = name; 

     } 

} 

Since Address is not Serializable, we are getting NotSerializableException while serializing the instance of Employee class.

How to fix the Serialization in the case of Association?

Using the transient keyword:

In case the class refers to non-serializable objects and these objects should not be serialized, then, you can declare these objects as transient. Once a field of a class is declared as transient, then, it is ignored by the serializable runtime.

Using the static keyword:

In serialization, static variables are not serialized, so during deserialization, static variable value will load the class.

Make it a Serializable object:

All the objects within an object must be Serializable.