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What is Retention policy in java annotations?


Description:

  • A retention policy determines at what point annotation should be discarded.
  • Java defined 3 types of retention policies through java.lang.annotation.RetentionPolicy enumeration. It has SOURCE, CLASS and RUNTIME.
  • Annotation with retention policy SOURCE will be retained only with source code, and discarded during compile time.
  • Annotation with retention policy CLASS will be retained till compiling the code, and discarded during runtime.
  • Annotation with retention policy RUNTIME will be available to the JVM through runtime.
  • The retention policy will be specified by using java built-in annotation @Retention, and we have to pass the retention policy type.
  • The default retention policy type is CLASS.


Code:
package com.java2novice.annotations;

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

@Retention(RetentionPolicy.RUNTIME)
public @interface MySampleAnn {

	String name();
	String desc();
}

class MyAnnTest{
	
	@MySampleAnn(name = "test1", desc = "testing annotations")
	public void myTestMethod(){
		//method implementation
	}
}
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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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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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