Given the code fragment: How can you get all property names of a JMS message in the JMS consumer onMessage operation?

Question

Options

• AString [] props = msg.getPropertyNames();
• BEnumeration props = msg.getPropertyNames();С. Iterator props = msg.getPropertyNames();
• CList<String> props = msg.getProperties();

• A
  89% (55)
• B
  8% (5)
• C
  3% (2)

Explanation

Note on the stated correct answer: There appears to be an error in this question. In the actual JMS API (javax.jms.Message), getPropertyNames() returns an Enumeration, not a String[]. The real correct answer is B.

Message.getPropertyNames() is defined in the JMS spec to return Enumeration (or Enumeration<String> in JMS 2.0), making B the only type-compatible assignment. A (String[]) is wrong because getPropertyNames() does not return an array - that type never appears in the JMS Message API. C (Iterator) is wrong because the JMS API predates the Java Collections framework and deliberately chose Enumeration over Iterator. D (List<String> via getProperties()) is wrong because no such method getProperties() exists on javax.jms.Message at all.

Memory tip: JMS is a legacy API - think "old school Java." Enumeration is the pre-Collections-framework equivalent of Iterator, so whenever you see JMS returning a set of names, think Enumeration, not List, Iterator, or arrays.

If your exam source marks A as correct, flag it - it conflicts with the javax.jms.Message Javadoc.

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