java - How do different retention policies affect my annotations?

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

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