Java.Serialization.Describe the serialization/deserialization process using Serializable.

🔹 1. Mark the Class as Serializable

To make a class eligible for serialization:

import java.io.Serializable;

public class Person implements Serializable {
    private static final long serialVersionUID = 1L; // Optional but recommended

    String name;
    int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

✅ This tells Java: “You can save and restore objects of this class.”

🔹 2. Serialize the Object (Write to a File/Stream)

You use ObjectOutputStream to write the object to a file as a byte stream:

import java.io.*;

Person p = new Person("Stanley", 33);

try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("person.ser"))) {
    out.writeObject(p);
}

🧠 Java will:

• Check that Person implements Serializable
• Write the object once, even if referenced multiple times
• Store the object structure, field values, and object graph

🔹 3. Deserialize the Object (Read from a File/Stream)

To reconstruct the object later:

Person loaded;

try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("person.ser"))) {
    loaded = (Person) in.readObject();
}
System.out.println(loaded.name + ", " + loaded.age); // Stanley, 33

🧠 Java will:

• Read the byte stream
• Use the serialVersionUID to ensure class compatibility
• Reconstruct the object in new heap memory
• Restore all non-transient fields

🔑 What Happens Internally

Step	Internal Behavior
Write (writeObject)	Object graph is traversed, serialized, and referenced via ID
Store	Fields, type info, reference map are written to the file
Read (readObject)	Objects are reconstructed; shared references are preserved
== between shared objects	Still true, because Java reuses deserialized instances

⚠️ Special Cases

Feature	Behavior
transient fields	Not saved to file
static fields	Not saved (belong to class, not instance)
serialVersionUID mismatch	Throws InvalidClassException
Not implementing Serializable	Throws NotSerializableException

🔥 Bonus: Add transient to skip fields

transient String password;

This will not be saved to the file.

🧪 Full Example (Mini Demo)

// Serializable class
public class Person implements Serializable {
    private static final long serialVersionUID = 1L;
    String name;
    int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

// Save
Person p = new Person("Stanley", 33);
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("p.ser"));
out.writeObject(p);
out.close();

// Load
ObjectInputStream in = new ObjectInputStream(new FileInputStream("p.ser"));
Person p2 = (Person) in.readObject();
in.close();

System.out.println(p2.name + ", " + p2.age); // Stanley, 33

🧵 TL;DR

Step	Tool	Description
1. Mark class	implements Serializable	Makes it eligible for serialization
2. Save	ObjectOutputStream.writeObject(obj)	Writes object to stream/file
3. Load	ObjectInputStream.readObject()	Reads and reconstructs the object
Version control	serialVersionUID	Ensures class compatibility