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Java's serialization provides an elegant, and easy to use mechanism for making an object's state persistent. While controlling object serialization, we might have a particular object data member that we do not want the serialization mechanism to save. The modifier transient can be applied to field members of a class to turn off serialization on these field members. Every field marked as transient will not be serialized. You use the transient keyword to indicate to the Java virtual machine that the transient variable is not part of the persistent state of an object. The transient modifier applies to variables only. Like other variable modifiers in the Java system, you use transient in a class or instance variable declaration like this: class TransientExample { transient int hobo; . . . } This statement declares an integer variable named hobo that is not part of the persistent state of the TransientExample class.

Serialization is another important topic that needs to be well prepared whe n you are going fro interview. We have collected important topics that are asked by interview panel of one of the major companies. Just check them below How many methods in the Serializable interface? Which methods of Serializable interface should I implement? There is no method in the Serializable interface. It’s an empty interface which does not contain any methods. The Serializable interface acts as a marker, telling the object serialization tools that the class is serializable. So we do not implement any methods.  What is the difference between Serializalble and Externalizable interface? How can you control over the serialization process i.e. how can you customize the seralization process? When you use Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject() two methods to control more complex object serailization process. When ...

Q1) What is Serialization? Ans) Serializable is a marker interface. When an object has to be transferred over a network ( typically through rmi or EJB) or persist the state of an object to a file, the object Class needs to implement Serializable interface. Implementing this interface will allow the object converted into bytestream and transfer over a network. Q2) What is use of serialVersionUID? Ans) During object serialization, the default Java serialization mechanism writes the metadata about the object, which includes the class name, field names and types, and superclass. This class definition is stored as a part of the serialized object. This stored metadata enables the deserialization process to reconstitute the objects and map the stream data into the class attributes with the appropriate type Everytime an object is serialized the java serialization mechanism automatically computes a hash value. ObjectStreamClass's computeSerialVersionU...

Here is a summary of some rules of Java serialization: An object is serializable only if its class or its superclass implements the Serializable (or   Externalizable ) interface. An object is serializable (itself implements the Serializable interface) even if its superclass is not. However, the first superclass in the hierarchy of the serializable class, that does not implements Serializable interface, MUST have a no-arg constructor. If this is violated, readObject() will produce a java.io.InvalidClassException in runtime. The no-arg contructor of every non-serializable superclass will run when an object is deserialized. However, the deserialized objects? constructor does not run when it is deserialized. The class must be visible at the point of serialization.

In Effective Java Programming Language Guide , Joshua Bloch wrote many thoughts about serialization. Here is a summary of some precautions recommended: If you do not get to the effort to design a custom serialized form, but merely accept the default, the class's private and package instance fields becomes part of its exported API. In this way, it decreases the flexibility to change a class's implementation once it has been released. Serial versions UIDs are automatically generated based on the name of the class, the names of their interfaces, and of all public and protected members. If a change is made to the class but you do not provide a custom serial UID the compatibility will be broken. Serialization is a extralinguistic mechanism, deserialization is a hidden constructor. All the invariants for an object should be checked in the process of deserializing an object, as a constructor would do. Classes design for i...

In Effective Java Programming Language Guide , Joshua Bloch wrote many thoughts about serialization. Here is a summary of some precautions recommended: If you do not get to the effort to design a custom serialized form, but merely accept the default, the class's private and package instance fields becomes part of its exported API. In this way, it decreases the flexibility to change a class's implementation once it has been released. Serial versions UIDs are automatically generated based on the name of the class, the names of their interfaces, and of all public and protected members. If a change is made to the class but you do not provide a custom serial UID the compatibility will be broken. Serialization is a extralinguistic mechanism, deserialization is a hidden constructor. All the invariants for an object should be checked in the process of deserializing an object, as a constructor would do.

How many methods in the Serializable interface? Which methods of Serializable interface should I implement? There is no method in the Serializable interface. It’s an empty interface which does not contain any methods. The Serializable interface acts as a marker, telling the object serialization tools that the class is serializable. So we do not implement any methods. What is the difference between Serializalble and Externalizable interface? How can you control over the serialization process i.e. how can you customize the seralization process? When you use Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject() two methods to control more complex object serailization process. When you use Externalizable interface, you have a complete control over your class's serialization process. This interface contains two methods namely readExternal and writeExternal. You should implement these methods and write the logi...