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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Knowledge Centre
What is daemon thread?
Daemon thread is a low priority thread. It runs intermittently in the back ground, and takes care of the garbage collection operation for the java runtime system. By calling setDaemon() method is used to create a daemon thread.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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