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<h3>Java 5 annotations</h3>

<p>Java 5 annotations are standardized through the <table class="wysiwyg-macro" data-macro-name="unmigrated-inline-wiki-markup" data-macro-parameters="atlassian-macro-output-type=BLOCK" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e3VubWlncmF0ZWQtaW5saW5lLXdpa2ktbWFya3VwOmF0bGFzc2lhbi1tYWNyby1vdXRwdXQtdHlwZT1CTE9DS30&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>{link:JSR-175 specification|http://www.jcp.org/en/jsr/detail?id=175}{link}</pre></td></tr></table>. When you compile annotated source code the <code>javac</code> compiler will embed the annotations in the compiled class, and this information can then be read back using the reflection API.</p>

<p>Annotations in Java 5 are first class citizen through the <code>@interface</code> keyword.</p>

<table class="wysiwyg-macro" data-macro-name="code" data-macro-default-parameter="java" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGU6amF2YX0&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
// A Java 5 Annotation
public @interface Asynchronous {
    int timeout() default 5;
    String label();
}

// A Java 5 annotated method
@Asynchronous(timeout=5, label="will run for a while")
public Object someMethod() {
    ...
}
</pre></td></tr></table>

<h3>backport175 annotations for Java 1.3/1.4</h3>

<p><strong>backport175</strong> is an implementation of the <table class="wysiwyg-macro" data-macro-name="unmigrated-inline-wiki-markup" data-macro-parameters="atlassian-macro-output-type=BLOCK" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e3VubWlncmF0ZWQtaW5saW5lLXdpa2ktbWFya3VwOmF0bGFzc2lhbi1tYWNyby1vdXRwdXQtdHlwZT1CTE9DS30&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>{link:JSR-175 specification|http://www.jcp.org/en/jsr/detail?id=175}{link}</pre></td></tr></table> for Java 1.3/1.4 which provides the same user experience as regular Java 5 annotations. </p>

<p>Annotations are defined using a regular Java interface (hence providing strongly typed access to annotation values), and annotated source code appears in the form of doclet in the JavaDoc part.</p>

<p>The backport175 compiler (available through command line or as an <a class="confluence-link" href="/display/175/Ant+task" data-linked-resource-id="18668" data-linked-resource-type="page" data-linked-resource-default-alias="Ant task" data-base-url="http://docs.codehaus.org">Ant task</a>) allows you to <a class="confluence-link" href="/display/175/Compiling+annotations" data-linked-resource-id="18662" data-linked-resource-type="page" data-linked-resource-default-alias="Compiling annotations" data-base-url="http://docs.codehaus.org">post-compile</a> your classes to embed the annotation information inside the class' bytecode. The annotations are bytecode compatible with regular Java 5 annotations and therefore can be treated the same by tools, regular Java reflection (on Java 5) etc.</p>

<p>Note: it is advised to have a space between the annotation and its value as below though not mandatory.</p>

<table class="wysiwyg-macro" data-macro-name="code" data-macro-default-parameter="java" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGU6amF2YX0&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
// A Java 1.3/1.4 Annotation with backport175
public interface Asynchronous {
    /**
     * Default value is supported through this specific annotation
     *
     * @org.codehaus.backport175.DefaultValue (5)
     */
    int timeout();

String label();
}

// A Java 1.3/1.4 annotated method
/**
 * @Asynchronous (timeout=5, label="will run for a while")
 */
public Object someMethod() {
    ...
}
</pre></td></tr></table>

<p>The annotations can then be accessed using the API in the <code>org.codehaus.backport175.reader.Annotations</code> class which allows to retrieve reflectively both regular Java 5 annotations and Java 1.3/1.4 annotations in a consistent way, allowing you to adopt annotation driven development even without Java 5, while having a simple migration path. For more information on how to access annotations, read <a class="confluence-link" href="/display/175/Reading+annotations" data-linked-resource-id="18674" data-linked-resource-type="page" data-linked-resource-default-alias="Reading annotations" data-base-url="http://docs.codehaus.org">this section</a>.</p>