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JAVA EXAMPLE PROGRAMS

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How to get annotations at runtime using java reflection?


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 an annotation values during runtime using java reflection.


Code:
package com.java2novice.annotations;

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

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

public class MyAnnotationTest {

	@MyAnnotation(key="site", value="java2novice.com")
	public void myAnnotationTestMethod(){
		
		try {
			Class<? extends MyAnnotationTest> cls = this.getClass();
			Method mth = cls.getMethod("myAnnotationTestMethod");
			MyAnnotation myAnno = mth.getAnnotation(MyAnnotation.class);
			System.out.println("key: "+myAnno.key());
			System.out.println("value: "+myAnno.value());
		} 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[]){
		
		MyAnnotationTest mat = new MyAnnotationTest();
		mat.myAnnotationTestMethod();
	}
}

Output:
key: site
value: java2novice.com
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Knowledge Centre
Domain Naming Service(DNS)
It is very difficult to remember a set of numbers (IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For example, www.java2novice.com implies com is the domain name reserved for US commercial sites, java2novice is the name of the company and www is the name of the specific computer, which is java2novice's server.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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