annotations retention policy

Question

Can anyone explain me in a clear way what does meaning the java.lang.annotation.RetentionPolicy costants SOURCE, CLASS, RUNTIME?

and the term ""retaining annotation"" !!!

Answer 1

• RetentionPolicy.SOURCE: Discard during the compile. These annotations don't make any sense after the compile has completed, so they aren't written to the bytecode.
  Example: @Override, @SuppressWarnings

• RetentionPolicy.CLASS: Discard during class load. Useful when doing bytecode-level post-processing. Somewhat surprisingly, this is the default.

• RetentionPolicy.RUNTIME: Do not discard. The annotation should be available for reflection at runtime. Example: @Deprecated

Source:

http://www.oracle.com/technology/pub/articles/hunter_meta_2.html

Answer 2

According to your comments about class decompilation, here is how I think it should work:

• RetentionPolicy.SOURCE: Won't appear in the decompiled class

• RetentionPolicy.CLASS: Appear in the decompiled class, but can't be inspected at run-time with reflection with getAnnotations()

• RetentionPolicy.RUNTIME: Appear in the decompiled class, and can be inspected at run-time with reflection with getAnnotations()