What is meaning of Plain Old Java Object (POJO)?

Question

What does the term Plain Old Java Object (POJO) mean? I couldn\'t find anything explanatory enough.

POJO\'s Wikipedia page says that POJO is an ordinary Jav

Answer 1

Usage of the term implies what it's supposed to tell you. If, for example, a dependency injection framework tells you that you can inject a POJO into any other POJO they want to say that you do not have to do anything special: there is no need to obey any contracts with your object, implement any interfaces or extend special classes. You can just use whatever you've already got.

UPDATE To give another example: while Hibernate can map any POJO (any object you created) to SQL tables, in Core Data (Objective C on the iPhone) your objects have to extend NSManagedObject in order for the system to be able to persist them to a database. In that sense, Core Data cannot work with any POJO (or rather POOCO=PlainOldObjectiveCObject) while Hibernate can. (I might not by 100% correct re Core Data since I just started picking it up. Any hints / corrections are welcome :-) ).

Answer 2

The whole point of a POJO is simplicity and you appear to be assuming its something more complicated than it appears.

If a library supports a POJO, it implies an object of any class is acceptible. It doesn't mean the POJO cannot have annotations/interface or that they won't be used if they are there, but it is not a requirement.

IMHO The wiki-page is fairly clear. It doesn't say a POJO cannot have annotations/interfaces.