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JAVA EXAMPLE PROGRAMS

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How to get all annotations from a class?


Description:

  • Incase if any annotation is specifies its retention policy as RUNTIME, then those annotations can be queried at runtime by any java program.
  • Below example code shows how to query all given annotations at runtime.


Code:
package com.java2novice.annotations;

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


@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnoOne{
	
	String key();
	String value();
}

@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnoTwo{
	
	int count();
}

public class MyMultipleAnns {

	@MyAnnoTwo(count=20)
	@MyAnnoOne(key="site", value="java2novice.com")
	public void myAnnotationTestMethod(){
		
		try {
			Class<? extends MyMultipleAnns> cls = this.getClass();
			Method mth = cls.getMethod("myAnnotationTestMethod");
			Annotation[] anns = mth.getAnnotations();
			for(Annotation an:anns){
				System.out.println(an);
			}
		} 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[]){
		
		MyMultipleAnns mat = new MyMultipleAnns();
		mat.myAnnotationTestMethod();
	}
}

Output:
@com.java2novice.annotations.MyAnnoTwo(count=20)
@com.java2novice.annotations.MyAnnoOne(key=site, value=java2novice.com)
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  10. What is single member annotation and how to process it?
Knowledge Centre
Difference between Enumeration and Iterator
The functionality of Enumeration and the Iterator are same. You can get remove() from Iterator to remove an element, while while Enumeration does not have remove() method. Using Enumeration you can only traverse and fetch the objects, where as using Iterator we can also add and remove the objects. So Iterator can be useful if you want to manipulate the list and Enumeration is for read-only access.
Famous Quotations
Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress.
-- Alfred A. Montapert

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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