Question

Can anyone explain in a clear way the practical differences between the java.lang.annotation.RetentionPolicy constants SOURCE, CLASS, and RUNTIME?

I’m also not exactly sure what the phrase “retaining annotation” means.

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:
The old URL is dead now
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