What "Deprecated" Means
You may have heard the term, "self-deprecating humor," or humor that minimizes the speaker's importance. A deprecated class or method is like that. It is no longer important. It is so unimportant, in fact, that you should no longer use it, since it has been superseded and may cease to exist in the future.
Java provides a way to express deprecation because, as a class evolves, its API (application programming interface) inevitably changes: methods are renamed for consistency, new and better methods are added, and fields change. But such changes introduce a problem. You need to keep the old API around until developers make the transition to the new one, but you don't want them to continue programming to the old API.
The ability to deprecate a class, method, or member field solves the problem. Java supports two mechanisms for deprecation: and an annotation, (supported starting with J2SE 5.0) and a Javadoc tag (supported since 1.1). Existing calls to the old API continue to work, but the annotation causes the compiler to issue a warning when it finds references to deprecated program elements. The Javadoc tag and associated comments warn users against using the deprecated item and tell them what to use instead.
When to Deprecate
When you design an API, carefully consider whether it supersedes an old API. If it does, and you wish to encourage developers (users of the API) to migrate to the new API, then deprecate the old API. Valid reasons to deprecate an API include:
- It is insecure, buggy, or highly inefficient
- It is going away in a future release
- It encourages bad coding practices
Deprecation is a reasonable choice in all these cases because it preserves "backward compatibility" while encouraging developers to change to the new API. Also, the deprecation comments help developers decide when to move to the new API, and so should briefly mention the technical reasons for deprecation.
It is not necessary to deprecate individual member fields (properties) of a deprecated class, unless of course you want to explain a specific point about a property.