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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
What is adapter class?
An adapter class provides the default implementation of all methods in an event listener interface. Adapter classes are very useful when you want to process only few of the events that are handled by a particular event listener interface. You can define a new class by extending one of the adapter classes and implement only those events relevant to you.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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