JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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What is marker annotation and how to process it at runtime?


Description:

  • Marker annotation doesnot contains any member declarations. By looking at presence of the annotation, we can do some specific actions.
  • By using isAnnotationPresent() method, we can check whether the annotation is present or not.


Code:
package com.java2novice.annotations;

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

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

public class MyMarkerAnnotation {

	@MyMarkerAnnot
	public void myAnnotationTestMethod(){
		
		try {
			Class<? extends MyMarkerAnnotation> cls = this.getClass();
			Method mth = cls.getMethod("myAnnotationTestMethod");
			if(mth.isAnnotationPresent(MyMarkerAnnot.class)){
				System.out.println("Hey... marker annotation is present.");
			} else {
				System.out.println("Marker annotation is not present.");
			}
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	public static void main(String a[]){
		
		MyMarkerAnnotation mat = new MyMarkerAnnotation();
		mat.myAnnotationTestMethod();
	}
}

Output:
Hey... marker annotation is present.
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List Of All Annotation (Metadata) Programs:

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  2. What is Retention policy in java annotations?
  3. How to get annotations at runtime using java reflection?
  4. How to get all annotations from a class?
  5. How to assign default values to custom annotations?
  6. What is marker annotation and how to process it at runtime?
  7. Built-in Java Annotations: @Deprecated example
  8. Built-in Java Annotations: @Override example
  9. Built-in Java Annotations: @SuppressWarnings example
  10. What is single member annotation and how to process it?
Knowledge Centre
When to use LinkedList or ArrayList?
Accessing elements are faster with ArrayList, because it is index based. But accessing is difficult with LinkedList. It is slow access. This is to access any element, you need to navigate through the elements one by one. But insertion and deletion is much faster with LinkedList, because if you know the node, just change the pointers before or after nodes. Insertion and deletion is slow with ArrayList, this is because, during these operations ArrayList need to adjust the indexes according to deletion or insetion if you are performing on middle indexes. Means, an ArrayList having 10 elements, if you are inserting at index 5, then you need to shift the indexes above 5 to one more.
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The greatest obstacle to discovery is not ignorance; it is the illusion of knowledge.
-- Daniel J. Boorstin

About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
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