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Annotations and Annotation Types

Annotations are notes in Java programs to instruct the Java compiler to do something. Java provides three standard annotations and four standard meta-annotations. An annotation type is a special interface type. An annotation is an instance of an annotation type. An annotation type has a name and members. The information contained in an annotation takes the form of key/value pairs. There can be zero or multiple pairs and each key has a specific type. It can be a String, int, or other Java types. Annotation types with no key/value pairs are called marker annotation types. Those with one key/value pair are referred to single-value annotation types. There are three annotation types in Java 5: Deprecated, Override, and Suppress Warnings. There are four other annotation types that are part of the java.lang.annotation package: Documented, Inherited, Retention, and Target. These four annotation types are used to annotate annotations,