Is it wrong to use Deprecated methods or classes in Java?

1. Is it wrong to use Deprecated methods or classes in Java?

From the definition of deprecated:

A program element annotated @Deprecated is one that programmers are discouraged from using, typically because it is dangerous, or because a better alternative exists.

The method is kept in the API for backward compatibility for an unspecified period of time, and may in future releases be removed. That is, no, it's not wrong, but there is a better way of doing it, which is more robust against API changes.

2. What if I don't change any method and run my application with warnings that I have, will it create any performance issue.

Most likely no. It will continue to work as before the deprecation. The contract of the API method will not change. If some internal data structure changes in favor of a new, better method, there could be a performance impact, but it's quite unlikely.

The funniest deprecation in the Java API, is imo, the FontMetrics.getMaxDecent. Reason for deprecation: Spelling error.

Deprecated. As of JDK version 1.1.1, replaced by getMaxDescent().

You can still use deprecated code without performance being changed, but the whole point of deprecating a method/class is to let users know there's now a better way of using it, and that in a future release the deprecated code is likely to be removed.

Terminology

From the official Sun glossary:

deprecation: Refers to a class, interface, constructor, method or field that is no longer recommended, and may cease to exist in a future version.

From the how-and-when to deprecate guide:

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 It is so unimportant, in fact, that you should no longer use it, since it has been superseded and may cease to exist in the future.

The @Deprecated annotation went a step further and warn of danger:

A program element annotated @Deprecated is one that programmers are discouraged from using, typically because it is dangerous, or because a better alternative exists.

References

• java.sun.com Glossary
• Language guide/How and When to Deprecate APIs
• Annotation Type Deprecated API

Right or wrong?

The question of whether it's right or wrong to use deprecated methods will have to be examined on individual basis. Here are ALL the quotes where the word "deprecated" appears in Effective Java 2nd Edition:

Item 7: Avoid finalizers: The only methods that claim to guarantee finalization are System.runFinalizersOnExit and its evil twin Runtime.runFinalizersOnExit. These methods are fatally flawed and have been deprecated.

Item 66: Synchronize access to shared mutable data: The libraries provide the Thread.stop method, but this method was deprecated long ago because it's inherently unsafe -- its use can result in data corruption.

Item 70: Document thread safety: The System.runFinalizersOnExit method is thread-hostile and has been deprecated.

Item 73: Avoid thread groups: They allow you to apply certain Thread primitives to a bunch of threads at once. Several of these primitives have been deprecated, and the remainder are infrequently used. [...] thread groups are obsolete.

So at least with all of the above methods, it's clearly wrong to use them, at least according to Josh Bloch.

With other methods, you'd have to consider the issues individually, and understand WHY they were deprecated, but generally speaking, when the decision to deprecate is justified, it will tend to lean toward wrong than right to continue using them.

Related questions

• Difference between a Deprecated and Legacy API?

Aside from all the excellent responses above I found there is another reason to remove deprecated API calls.

Be researching why a call is deprecated I often find myself learning interesting things about the Java/the API/the Framework. There is often a good reason why a method is being deprecated and understanding these reasons leads to deeper insights.

So from a learning/growing perspective, it is also a worthwhile effort