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
Class, Constructor and Primitive data types
Class is a template for multiple objects with similar features and it is a blue print for objects. It defines a type of object according to the data the object can hold and the operations the object can perform. Constructor is a special kind of method that determines how an object is initialized when created. Primitive data types are 8 types and they are: byte, short, int, long, float, double, boolean, char.
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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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