From the Java doc:
CLASS:
Annotations are to be recorded in the class file by the compiler but need not be retained by the VM at run time.
RUNTIME:
Annotations are to be recorded in the class file by the compiler and retained by the VM at run time, so they may be read reflectively.
SOURCE:
Annotations are to be discarded by the compiler.
I understand the usages of RUNTIME (in order to use annotation with reflection) and CLASS (for the compiler) but I don’t understand when it can be usefull to use
@Retention(RetentionPolicy.SOURCE)
Can you explain?
Advertisement
Answer
Things like @SuppressWarnings, @Override are annotations used by the compiler – not needed at runtime. For those RetentionPolicy.SOURCE would make sense. Also annotations can be used to generate code (look at Spring ROO) – such annotation are also not required at run time.