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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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List Of All Annotation (Metadata) Programs:

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  2. What is Retention policy in java annotations?
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  4. How to get all annotations from a class?
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Knowledge Centre
When to use LinkedList or ArrayList?
Accessing elements are faster with ArrayList, because it is index based. But accessing is difficult with LinkedList. It is slow access. This is to access any element, you need to navigate through the elements one by one. But insertion and deletion is much faster with LinkedList, because if you know the node, just change the pointers before or after nodes. Insertion and deletion is slow with ArrayList, this is because, during these operations ArrayList need to adjust the indexes according to deletion or insetion if you are performing on middle indexes. Means, an ArrayList having 10 elements, if you are inserting at index 5, then you need to shift the indexes above 5 to one more.
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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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