In Enterprise JavaBeans (EJB), can you tell whether a session bean is stateful or stateless just by looking at its Java interface signature?

Introduction / Context:
Enterprise JavaBeans (EJB) define several types of session beans, including stateful and stateless beans. These beans may expose local or remote interfaces that declare business methods. Interviewers sometimes ask whether you can tell if a session bean is stateful or stateless just by examining the Java interface, in order to test whether you understand how bean type is defined in EJB and where that information is stored.

Given Data / Assumptions:

• We are working with EJB session beans (stateful and stateless).
• Each bean may have a business interface that declares method signatures.
• Bean type (stateful or stateless) is defined using annotations such as @Stateful or @Stateless or via deployment descriptors.
• The question is about identifying bean type by looking only at the interface signature.

Concept / Approach:
In EJB, the distinction between a stateful and a stateless session bean concerns how the container manages conversational state between method calls. A stateful session bean maintains client specific state across multiple invocations, whereas a stateless session bean does not retain such state and can be pooled and reused across clients. This behavioural difference is not represented in the Java method signatures. Instead, bean type is declared using annotations (@Stateful or @Stateless) on the bean implementation class or in the deployment descriptor. The method names, parameters, return types, or interface extends clauses do not inherently encode whether a bean is stateful or stateless, so you cannot infer the bean type from the interface alone.

Step-by-Step Solution:
Step 1: Consider what the business interface of a session bean contains: method signatures that define operations the bean provides to clients. Step 2: Recognise that both stateful and stateless beans can have identical looking business interfaces; they may expose the same set of operations. Step 3: Note that bean type is specified in the implementation class using @Stateful or @Stateless, or in XML deployment descriptors, not in the interface. Step 4: Understand that any naming patterns, such as methods starting with set or get, are conventions and not enforced indicators of bean type. Step 5: Conclude that, without seeing the implementation class annotations or descriptor metadata, you cannot reliably tell whether the bean is stateful or stateless based solely on its interface signature.

Verification / Alternative check:
To verify this, imagine two beans that share the same business interface AccountService with methods like credit, debit, and getBalance. One implementation might be annotated @Stateful to hold temporary conversational state for a wizard style interaction, and another might be annotated @Stateless to treat each call independently. The interface AccountService is identical in both cases, yet the bean types differ. This example shows that knowing the interface alone does not tell you whether the underlying bean is stateful or stateless. You must inspect the annotations or the deployment descriptor configuration to know the difference.

Why Other Options Are Wrong:
Option Yes, a stateful session bean always has method names starting with "set", while a stateless session bean does not: Method naming patterns are conventions and not enforced indicators of bean type. Option Yes, a stateless session bean interface must extend java.io.Serializable, while a stateful session bean interface does not: The EJB specification does not require such inheritance to distinguish bean types. Option Yes, a stateful session bean interface must declare a special init method, while a stateless one must not: Although beans may have lifecycle callbacks, these are defined through annotations such as @PostConstruct, not necessarily through special methods visible in the business interface.

Common Pitfalls:
A common misconception is to assume that stateful beans always have certain kinds of methods, such as setters, that reveal their stateful nature. In reality, both types of beans can expose a variety of operations, and the presence of state is managed by the container, not inferred from method names. Another pitfall is to rely on informal naming conventions, which may differ across projects. For exam answers, emphasise that bean type is defined in metadata (annotations or descriptors), not in the business interface signature.

Final Answer:
You cannot reliably determine whether a session bean is stateful or stateless just from its interface signature; you need to see the bean annotations or deployment descriptor.