Java Metadata Facility

Synonyms

Java annotations; Java metadata facility; JSR 175

Definition

The Java Metadata Facility is introduced by Java Specification Request (JSR) 175 [1], and incorporated into the Java language specification [2] in version 1.5 of the language. The specification allows annotations on Java program elements: classes, interfaces, methods, and fields. Annotations give programmers a uniform way to add metadata to program elements that can be used by code checkers, code generators, or other compile-time or runtime components.

Annotations are defined by annotation types. These are defined the same way as interfaces, but with the symbol “@”; preceding the “interface” keyword. There are additional restrictions on defining annotation types:

• 1. They cannot be generic.

• 2. They cannot extend other annotation types or interfaces.

• 3. Methods cannot have any parameters.

• 4. Methods cannot have type parameters.

• 5. Methods cannot throw exceptions.

• 6. The return type of methods of an annotation type must...