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 fail-fast in java?
A fail-fast system is nothing but immediately report any failure that is likely to lead to failure. When a problem occurs, a fail-fast system fails immediately. In Java, we can find this behavior with iterators. Incase, you have called iterator on a collection object, and another thread tries to modify the collection object, then concurrent modification exception will be thrown. This is called fail-fast.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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