Create Custom Annotation In java

Annotations are meta data to be used by compiler or run time environment.Creating your custom annotation in java is very simple .

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
 String value() default "myAnootation";
 String[] arr() default {"testarr"};
}

Here , the RetentionPolicy.RUNTIME will determine whether the annotation will be present at run time or not.To test the annotation and get the values , let's create a test class

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;

/**
 * 
 * 
 * @author Abhishek Somani
 * 
 */
public class MyAnnotationTest {
 
 @MyAnnotation(value="test my annotation",arr={"my arr test"})
 public void annotationTest()
 {
  
 }
 
 
 public static void main(String[] args) {
  Method[] methods = MyAnnotationTest.class.getDeclaredMethods();
  
  for(Method m : methods)
  {
   for(Annotation a : m.getAnnotations())
   {
    if ( a instanceof MyAnnotation)
    {
     MyAnnotation ann = (MyAnnotation)a;
     System.out.println(ann.value());
     for(String s : ann.arr())
     {
      System.out.println(s);
     }
    }
   }
  }
  
  
  
 }

}

Here annotation is on method level , we can access the annotation element values using reflection on method.If the do not specify RetentionPolicy as RUNTIME , the jvm will ignore this annotation and we will not be able to access this annotation.

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