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2010-06-01T05:06:44Z

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в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

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== Creating Annotations ==

Annotation is created based on the interface.
<OL><LI>Adding "@" before the keyword interface to declare an annotation type.</LI><LI>All annotations consist only method declarations.</LI><LI>These methods act much like fields.</LI></OL>
Our first annotation type:



<source lang="java">
// A simple annotation type.
@interface MyAnnotation {
String stringValue();
int intValue();
}</source>



== default values in an annotation. ==



<source lang="java">
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Method;
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnno {
String str() default "Testing";
int val() default 9000;
}
class Meta3 {
@MyAnno()
public static void myMeth() {
Meta3 ob = new Meta3();
try {
Class c = ob.getClass();
Method m = c.getMethod("myMeth");
MyAnno anno = m.getAnnotation(MyAnno.class);
System.out.println(anno.str() + " " + anno.val());
} catch (NoSuchMethodException exc) {
System.out.println("Method Not Found.");
}
}
public static void main(String args[]) {
myMeth();
}
}</source>



== Define new annotation type ==

<OL><LI>All annotation types automatically extend the Annotation interface.</LI><LI>Annotation is a super-interface of all annotations.</LI><LI>It overrides hashCode( ), equals( ), and toString() defined by Object.</LI><LI>It defines annotationType( ), which returns a Class object that represents the invoking annotation.</LI><LI>When you apply an annotation, you give values to its members.</LI></OL>



<source lang="java">
// A simple annotation type.
@interface MyAnnotation {
String stringValue();
int intValue();
}
public class MainClass {
// Annotate a method.
@MyAnnotation(stringValue = "Annotation Example", intValue = 100)
public static void myMethod() {
}
}</source>



== Specifying a Retention Policy ==

A retention policy determines at what point an annotation is discarded.
<OL><LI>SOURCE: annotation retained only in the source file and is discarded during compilation.</LI><LI>CLASS: annotation stored in the .class file during compilation, not available in the run time.</LI><LI>RUNTIME: annotation stored in the .class file and available in the run time.</LI><LI>They are defined java.lang.annotation.RetentionPolicy enumeration.</LI></OL>
A retention policy is specified using Java"s built-in annotations: @Retention.



<source lang="java">
@Retention(retention-policy)</source>

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Admin: 1 версия

в 17:44, 31 мая 2010