JAVA EE: Java Tutorial: Annotations in java | Java annotations [Type of annotation]

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Java Tutorial: Annotations in java | Java annotations [Type of annotation]

MarkerAnnotationDemo.java

@interface MyMarkerAnnotation
{

}

public class MarkerAnnotationDemo
{
    @MyMarkerAnnotation
    public void display()
    {
        System.out.println("Hi");
    }

    public static void main(String args[])
    {
        MarkerAnnotationDemo markerAnnotationDemo = new MarkerAnnotationDemo();
        markerAnnotationDemo.display();
    }
}

Output

Hi

SingleValueAnnotationDemo.java

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

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@interface MySingleValueAnnotation
{
    int getValue();
}

class Display
{
    @MySingleValueAnnotation(getValue = 20)
    public void displayHi()
    {
        System.out.println("Hi");
    }
}

public class SingleValueAnnotationDemo
{

    public static void main(String[] args) throws NoSuchMethodException,
            SecurityException
    {
        Display display = new Display();
        Method method = display.getClass().getMethod("displayHi");

        MySingleValueAnnotation msva = method
                .getAnnotation(MySingleValueAnnotation.class);

        System.out.println("value is: " + msva.getValue());

    }

}

Output

value is: 20

MultiValueAnnotationDemo.java

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

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@interface MyMultiValueAnnotation
{
    int getValue();

    String getMessage();
}

class Message
{
    @MyMultiValueAnnotation(getValue = 500, getMessage = "Welcome")
    public void displayHi()
    {
        System.out.println("Hi");
    }
}

public class MultiValueAnnotationDemo
{

    public static void main(String[] args) throws NoSuchMethodException,
            SecurityException
    {
        Message message = new Message();
        Method method = message.getClass().getMethod("displayHi");

        MyMultiValueAnnotation mmva = method
                .getAnnotation(MyMultiValueAnnotation.class);

        System.out.println("value is: " + mmva.getValue());
        System.out.println("message is: " + mmva.getMessage());

    }

}