Serialization (Serializable) is automatic using reflection—the JVM uses introspection to save all non-transient fields. Externalization (Externalizable) gives the developer full control via writeExternal() and readExternal() methods. Externalization is faster and more secure but requires manual coding.
Serialization: Taking a photo of a house (captures everything). Externalization: Writing down only specific dimensions and materials to rebuild the house (more efficient and selective).
Why would you choose Externalizable over Serializable in production code? Provide trade-offs.