Object serialization in Java converts an object's state into a byte stream suitable for storage or transmission. Deserialization reconstructs the object from that byte stream. This capability is enabled by implementing the java.io.Serializable interface.

Implementing Serializable

A class must implement Serializable—a marker interface with no methods—to support serialization:

import java.io.Serializable;

public class DataRecord implements Serializable {
    private static final long serialVersionUID = 42L;
    // fields and methods
}

Serializing an Object

Use ObjectOutputStream to write an object to a file or stream:

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;

public class SerializeDemo {
    public static void main(String[] args) {
        DataRecord record = new DataRecord();
        try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("data.ser"))) {
            out.writeObject(record);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

Deserializing an Object

Reconstruct the object using ObjectInputStream:

import java.io.FileInputStream;
import java.io.ObjectInputStream;

public class DeserializeDemo {
    public static void main(String[] args) {
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("data.ser"))) {
            DataRecord record = (DataRecord) in.readObject();
            // use the restored object
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

Special Considerations

• Non-serializable references: If a serializable object holds a refeernce to a non-serializable object, serialization fails with NotSerializableException.
• Version control: The serialVersionUID field ensures compatibility between serialized data and class versions. Omitting it may cause version mismatch issues.
• Custom logic: Define private void writeObject(java.io.ObjectOutputStream) and private void readObject(java.io.ObjectInputStream) to override default serialization behavior.

Key Points

• Only instances of classes implementing Serializable can be serialized.
• Static and transient fields are excluded from serialization.
• Serialization captures runtime state, not code or method definitions.
• I/O exceptions must be handled during serialization operations.