Why RetentionPolicy.RUNTIME is used for @Deprecated annotation? [duplicate]

Question

Below is the documentation of @Deprecated annotation.

/**
 * A program element annotated @Deprecated is one that programmers
 * are discouraged from using, typically because it is dangerous,
 * or because a better alternative exists.  Compilers warn when a
 * deprecated program element is used or overridden in non-deprecated code.
 *
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(value={CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, PARAMETER, TYPE})
public @interface Deprecated {
}

My question is: @Deprecated (a marker annotation) is for the programmer to indicate that this method/ field/ package... is discouraged from using it, then why RetentionPolicy is set to RUNTIME why not RetentionPolicy.CLASS is used?

Answer 1

Reflection in Java can be used to read annotations of a class at runtime. If RetentionPolicy.CLASS were used then the @Deprecated annotation would not be available to be read like this.

As an example, a reflective program might read in a user-provided class, and execute all non-deprecated static methods without any arguments. Maybe someone can come up with a better example than that. Some reason why a unit testing framework might make use of it perhaps.