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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  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
What is transient variable?
Transient variables cannot be serialized. During serialization process, transient variable states will not be serialized. State of the value will be always defaulted after deserialization.
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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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