Annotations in java

• Java Annotation is a tag that represents the metadata i.e. attached with class, interface, methods or fields to indicate some additional information which can be used by java compiler and JVM.
• Annotations in Java are used to provide additional information, so it is an alternative option for XML and Java marker interfaces.

Creating Custom Annotation in java

• Marker Annotation.
• Single Value Annotation.
• Multi Value Annotation

Below is the Example of Multi Value Annotation :

package com.annotation.demo;

import java.lang.annotation.Annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Inherited // Annotation will be available to all child classes
@Documented // Annotation will be available in the documentation
@Target(ElementType.TYPE) //Type - Annotation on class 
@Retention(RetentionPolicy.RUNTIME) // Annotation avialability (SOURCE,CLASS,RUNTIME)
@interface Bird{
	String name() default "Bird";
	boolean doesFly() default true;
}

@Bird(name="Hedwig",doesFly=true)
class Owl{
	boolean nocternal;
	boolean rotate360;
	
	public Owl(boolean nocternal, boolean rotate360) {
																											
		this.nocternal = nocternal;
		this.rotate360 = rotate360;
	}
	
}

public class AnnotationDemo3 {
	public static void main(String[] args) {
		Owl owl = new Owl(true,true);
		
		Class c = owl.getClass();
		Annotation an = c.getAnnotation(Bird.class);
		Bird bird = (Bird)an;
		System.out.println(bird.name());
		System.out.println("Can bird fly ? "+bird.doesFly());
	}
}

Output :