Annotations in Java

Annotations in Java
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

The Basics

Purpose:
- Annotations provide information/data about a program (that is not part of the program itself)
An Implication:
- Annotations do not have any impact on the program itself

Who/What Might Use Annotations

Kinds of Uses

Construction:
- Improve code quality (e.g., the @Override annotation)
Design:
- Provide features that are difficult to provide in other ways (e.g., the @Test annotation makes it possible for JUnit to easily identify tests without using method names)
Testing:
- Weight the importance of different tests

Syntax

Allowed Locations

Declaration Annotations:
- On declarations of classes, attributes, methods, and variables
Type Annotations:
- On the new operator
- On type casts
- On throws clauses
- On implements clauses
- Anywhere you can use a type
Annotation Annotations:
- On another annotation

Some Predefined Annotations

Declaration Annotations:
- @Deprecated indicates the member should no longer be used and will cause the compiler to generate a warning if it is
- @Override indicates the method should be overriding a method in a super class and will cause the compiler to generate an error if it isn't
- @SuppressWarnings tells the compiler to suppress warnings in a specific category ("unchecked" and or "deprecated")
Type Annotations:
- None exist - you must develop or acquire a checking framework that defines them
Annotation Annotations:
- @Documented indicates that the annotation should be included in Javadoc documentation
- @Retention indicates how the annotation should be stored (i.e., SOURCE, CLASS, or RUNTIME)
- @Target indicates the Java elements the annotation can be applied to