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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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Where can we use serialization?
Whenever an object has to sent over the network, those objects should be serialized. Also if the state of an object is to be saved, objects need to be serilazed.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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