CODEWITHSUNDEEP
javaannotations
Rexsung
Rexsung

Reputation: 555

Java Annotations not working

I'm trying to use Java annotations, but can't seem to get my code to recognize that one exists. What am I doing wrong? 

  import java.lang.reflect.*;
  import java.lang.annotation.*;

  @interface MyAnnotation{}


  public class FooTest
  { 
    @MyAnnotation
    public void doFoo()
    {       
    }

    public static void main(String[] args) throws Exception
    {               
        Method method = FooTest.class.getMethod( "doFoo" );

        Annotation[] annotations = method.getAnnotations();
        for( Annotation annotation : method.getAnnotations() )
            System.out.println( "Annotation: " + annotation  );

    }
  }

Upvotes: 23

Views: 15077

Answers (3)

James Davies
James Davies

Reputation: 9859

You need to specify the annotation as being a Runtime annotation using the @Retention annotation on the annotation interface.

i.e. 

@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnotation{}

Upvotes: 43

Sudipta Deb
Sudipta Deb

Reputation: 501

Use @Retention(RetentionPolicy.RUNTIME) Check the below code. It is working for me:

import java.lang.reflect.*;
import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnotation1{}

@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnotation2{}

public class FooTest {
    @MyAnnotation1
    public void doFoo() {
    }

    @MyAnnotation2
    public void doFooo() {
    }

    public static void main(String[] args) throws Exception {
        Method method = FooTest.class.getMethod( "doFoo" );
        for( Annotation annotation : method.getAnnotations() )
            System.out.println( "Annotation: " + annotation  );

        method = FooTest.class.getMethod( "doFooo" );
        for( Annotation annotation : method.getAnnotations() )
            System.out.println( "Annotation: " + annotation  );
    }
}

Upvotes: 3

Brandon Yarbrough
Brandon Yarbrough

Reputation: 38379

Short answer: you need to add @Retention(RetentionPolicy.RUNTIME) to your annotation definition.

Explanation:

Annotations are by default not kept by the compiler. They simply don't exist at runtime. This may sound silly at first, but there are lots of annotations that are only used by the compiler (@Override) or various source code analyzers (@Documentation, etc).

If you want to actually USE the annotation via reflection like in your example, you'll need to let Java know that you want it to make a note of that annotation in the class file itself. That note looks like this:

@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation{}

For more information, check out the official docs1 and especially note the bit about RetentionPolicy.

Upvotes: 26

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