When should a JPA entity implement the Serializable interface?

Question

Options

• Awhen JPA entities are used in the EJB Full container
• Bwhen JPA entities are used outside of the EJB Lite container
• Calways, because JPA entities are required to implement the Serializable interface
• Dwhen JPA entities are used as parameters or return values by the remote EJB operations

• A
  7% (2)
• B
  19% (5)
• C
  4% (1)
• D
  70% (19)

Explanation

Implementing Serializable is required when a JPA entity is passed as a parameter or returned from a remote EJB method, because remote calls use Java's serialization mechanism to marshal objects across the network (or JVM boundaries). Option A is wrong because the EJB Full container doesn't inherently mandate serialization - it's the remote interface that does. Option B inverts the logic; being "outside the EJB Lite container" is not a defined trigger for serialization. Option C is wrong because JPA itself makes no such requirement - the JPA spec explicitly states that entities should implement Serializable only if they need to be detached and passed around remotely, not universally.

Memory tip: Think "remote = serialize." Remote EJB calls cross a boundary that Java can't bridge without serialization, so any entity that travels over that wire must be serializable. If it stays local, it doesn't need to be.

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