![]() Another tool might remove all test methods from a class file so they are not shipped with the program after it has been tested.Īnnotations can be defined to have elements, such as elements can be processed by the tools that read the annotations. For example, the JUnit 4 testing tool (available at ) calls all methods that are labeled when testing a class. */ delimiters, whereas annotations are part of the code.īy itself, the annotation does not do anything. However, Javadoc comments occur inside /**. (A modifier is a keyword such as public or static.) The name of each annotation is preceded by an symbol, similar to Javadoc comments. In Java, an annotation is used like a modifier and is placed before the annotated item without a semicolon. The annotation annotates the checkRandomInsertions method. Here is an example of a simple annotation: public class M圜lass One of them processes source-level annotations, the other uses the Apache Bytecode Engineering Library to process class files, injecting additional bytecodes into annotated methods. We’ll then discuss the syntax rules in detail and finish the chapter with two advanced examples of annotation processing. We’ll start our discussion of annotations with the basic concepts and put them to use in a concrete example: We will mark methods as event listeners for AWT components, and show you an annotation processor that analyzes the annotations and hooks up the listeners. Here are some uses for annotations:Īutomatic generation of auxiliary files, such as deployment descriptors or bean information classesĪutomatic generation of code for testing, logging, transaction semantics, and so on There is a wide range of uses for annotations, and that generality can be confusing at first. Use annotations that your processing tool understands, then apply the processing tool to your code. To benefit from annotations, you need to select a processing tool. The Java compiler generates the same virtual machine instructions with or without the annotations. The tools can operate on the source level, or they can process class files into which the compiler has placed annotations.Īnnotations do not change the way in which your programs are compiled. Core Java, Volume II-Advanced Features, 10th EditionĪnnotations are tags that you insert into your source code so that some tool can process them.
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