Welcome back, Sujit Kumar Mishra

What is the difference between Serialization or Serializable and Externalization or Externalizable?

Serialization (Serializable):

1: Serialization is the process of converting an object into a byte stream so it can be saved to a file or sent over a network.

2: If a class implements Serializable, Java automatically handles the serialization of all its fields.

3: You don’t need to write any extra code, just implement the interface.

Example:

class Student implements Serializable {
    int id;
    String name;
}

Here, all fields (id, name) will be serialized automatically.

Externalization (Externalizable):

1: Externalization is also used to convert an object into a byte stream, but gives you full control over what and how to serialize.

2: You must implement the writeExternal() and readExternal() methods to manually specify which fields to serialize and how.

3: Useful when you want to exclude some fields or customize the process.

Example:

class Student implements Externalizable {
    int id;
    String name;

    public void writeExternal(ObjectOutput out) 
                                      throws IOException {
        out.writeInt(id);
        out.writeObject(name);
    }

    public void readExternal(ObjectInput in) 
                       throws IOException, ClassNotFoundException {
        id = in.readInt();
        name = (String) in.readObject();
    }
}

Here, you decide which fields to save and how.

Easy Way to Remember:

1: Serializable - Java does everything for you, just implement the interface.

2: Externalizable - You do everything yourself, write the methods to control serialization.

Summary Table:

Feature                    Serializable                    Externalizable

Control                    Automatic                    Manual

Methods

Required                    None                    writeExternal/readExternal

Usage                    Simple objects                    Custom serialization

In Short:

Serializable = automatic, easy

Externalizable = manual, flexible