JAVA EXAMPLE PROGRAMS

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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Knowledge Centre
What is wrapper class?
Everything in java is an object, except primitives. Primitives are int, short, long, boolean, etc. Since they are not objects, they cannot return as objects, and collection of objects. To support this, java provides wrapper classes to move primitives to objects. Some of the wrapper classes are Integer, Long, Boolean, etc.
Famous Quotations
The greatest obstacle to discovery is not ignorance; it is the illusion of knowledge.
-- Daniel J. Boorstin

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] or you can comment on the page.

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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