Java Annotations

Annotation is code about the code, that is metadata about the program itself. In other words, organized data about the code, embedded within the code itself. It can be parsed by the compiler, annotation processing tools and can also be made available at run-time too.

We have basic java comments infrastructure using which we add information about the code / logic so that in future, another programmer or the same programmer can understand the code in a better way. Javadoc is an additional step over it, where we add information about the class, methods, variables in the source code. The way we need to add is organized using a syntax. Therefore, we can use a tool and parse those comments and prepare a javadoc document which can be distributed separately.

Javadoc facility gives option for understanding the code in an external way, instead of opening the code the javadoc document can be used separately. IDE benefits using this javadoc as it is able to render information about the code as we develop. Annotations were introduced in JDK 1.5

Uses of Annotations

Annotations are far more powerful than java comments and javadoc comments. One main difference with annotation is it can be carried over to runtime and the other two stops with compilation level. Annotations are not only comments, it brings in new possibilities in terms of automated processing.

In java we have been passing information to compiler for long. For example take serialization, we have the keyword transient to tell that this field is not serializable. Now instead of having such keywords decorating an attribute annotations provide a generic way of adding information to class/method/field/variable. This is information is meant for programmers, automated tools, java compiler and runtime. Transient is a modifier and annotations are also a kind of modifiers.

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More than passing information, we can generate code using these annotations. Take webservices where we need to adhere by the service interface contract. The skeleton can be generated using annotations automatically by a annotation parser. This avoids human errors and decreases development time as always with automation.

Frameworks like Hibernate, Spring, Axis make heavy use of annotations. When a language needs to be made popular one of the best thing to do is support development of frameworks based on the language. Annotation is a good step towards that and will help grow Java.

When Not to Use Annotations

  • Do not over use annotation as it will pollute the code.
  • It is better not to try to change the behaviour of objects using annotations. There is sufficient constructs available in oops and annotation is not a better mechanism to deal with it.
  • We should not what we are parsing. Do not try to over generalize as it may complicate the underlying code. Code is the real program and annotation is meta.
  • Avoid using annotation to specify environment / application / database related information.

Annotation Structure

There are two main components in annotations. First is annotation type and the next is the annotation itself which we use in the code to add meaning. Every annotation belongs to a annotation type.

Annotation Type:

@interface  {
method declaration;

Annotation type is very similar to an interface with little difference.

  • We attach ‘@’ just before interface keyword.
  • Methods will not have parameters.
  • Methods will not have throws clause.
  • Method return types are restricted to primitives, String, Class, enums, annotations, and arrays of the preceding types.
  • We can assign a default value to method.

Meta Annotations

Annotations itself is meta information then what is meta annotations? As you have rightly guessed, it is information about annotation. When we annotate a annotation type then it is called meta annotation. For example, we say that this annotation can be used only for methods.

public @interface MethodInfo { }

Annotation Types

  1. Documented
    When a annotation type is annotated with @Documented then wherever this annotation is used those elements should be documented using Javadoc tool.
  2. Inherited
    This meta annotation denotes that the annotation type can be inherited from super class. When a class is annotated with annotation of type that is annotated with Inherited, then its super class will be queried till a matching annotation is found.
  3. Retention
    This meta annotation denotes the level till which this annotation will be carried. When an annotation type is annotated with meta annotation Retention, RetentionPolicy has three possible values:

    public @interface Developer {
    	String value();
    • Class
      When the annotation value is given as ‘class’ then this annotation will be compiled and included in the class file.
    • Runtime
      The value name itself says, when the retention value is ‘Runtime’ this annotation will be available in JVM at runtime. We can write custom code using reflection package and parse the annotation. I have give an example below.
    • Source
      This annotation will be removed at compile time and will not be available at compiled class.
  4. Target
    This meta annotation says that this annotation type is applicable for only the element (ElementType) listed. Possible values for ElementType are, CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, PARAMETER, TYPE.

    public @interface FieldInfo { }

Built-in Java Annotations

@Documented, @Inherited, @Retention and @Target are the four available meta annotations that are built-in with Java.

Apart from these meta annotations we have the following annotations.


When we want to override a method, we can use this annotation to say to the compiler we are overriding an existing method. If the compiler finds that there is no matching method found in super class then generates a warning. This is not mandatory to use @Override when we override a method. But I have seen Eclipse IDE automatically adding this @Override annotation. Though it is not mandatory, it is considered as a best practice.


When we want to inform the compiler that a method is deprecated we can use this. So, when a method is annotated with @Deprecated and that method is found used in some place, then the compiler generates a warning.


This is like saying, “I know what I am doing, so please shut up!” We want the compiler not to raise any warnings and then we use this annotation.

Custom Annotations

We can create our own annotations and use it. We need to declare a annotation type and then use the respective annotation is java classes.

Following is an example of custom annotation, where this annotation can be used on any element by giving values. Note that I have used @Documented meta-annotation here to say that this annotation should be parsed by javadoc.

 * Describes the team which wrote the code
public @interface Team {
    int    teamId();
    String teamName();
    String teamLead() default "[unassigned]";
    String writeDate();    default "[unimplemented]";

Annotation for the Above Example Type

... a java class ...
    teamId       = 73,
    teamName = "Rambo Mambo",
    teamLead = "Yo Man",
    writeDate     = "3/1/2012"
public static void readCSV(File inputFile) { ... }
... java class continues ...

Marker Annotations

We know what a marker interface is. Marker annotations are similar to marker interfaces, yes they don’t have methods / elements.

 * Code annotated by this team is supreme and need
 * not be unit tested - just for fun!
public @interface SuperTeam { }
... a java class ...
@SuperTeam public static void readCSV(File inputFile) { ... }
... java class continues ...

In the above see how this annotation is used. It will look like one of the modifiers for this method and also note that the parenthesis () from annotation type is omitted. As there are no elements for this annotation, the parenthesis can be optionally omitted.

Single Value Annotations

There is a chance that an annotation can have only one element. In such a case that element should be named value.

 * Developer
public @interface Developer {
    String value();
... a java class ...
public static void readCSV(File inputFile) { ... }
... java class continues ...

How to Parse Annotation

We can use reflection package to read annotations. It is useful when we develop tools to automate a certain process based on annotation.


package com.javapapers.annotations;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
public @interface Developer {
	String value();
package com.javapapers.annotations;
public class BuildHouse {
	@Developer ("Alice")
	public void aliceMethod() {
		System.out.println("This method is written by Alice");
	@Developer ("Popeye")
	public void buildHouse() {
		System.out.println("This method is written by Popeye");
package com.javapapers.annotations;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
public class TestAnnotation {
	public static void main(String args[]) throws SecurityException,
			ClassNotFoundException {
		for (Method method : Class.forName(
				"com.javapapers.annotations.BuildHouse").getMethods()) {
			// checks if there is annotation present of the given type Developer
			if (method
					.isAnnotationPresent(com.javapapers.annotations.Developer.class)) {
				try {
					// iterates all the annotations available in the method
					for (Annotation anno : method.getDeclaredAnnotations()) {
						System.out.println("Annotation in Method '" + method
								+ "' : " + anno);
						Developer a = method.getAnnotation(Developer.class);
						if ("Popeye".equals(a.value())) {
							System.out.println("Popeye the sailor man! "
									+ method);
				} catch (Throwable ex) {


Annotation in Method 'public void com.javapapers.annotations.BuildHouse.aliceMethod()' : @com.javapapers.annotations.Developer(value=Alice)
Annotation in Method 'public void com.javapapers.annotations.BuildHouse.buildHouse()' : @com.javapapers.annotations.Developer(value=Popeye)
Popeye the sailor man! public void com.javapapers.annotations.BuildHouse.buildHouse()

apt / javac for Annotation Processing

In previous version of JDK apt was introduced as a tool for annotation processing. Later apt was deprecated and the capabilities are included in javac compiler. javax.annotation.processing and javax.lang.model contains the api for processing.

This Core Java tutorial was added on 03/06/2012.



Comments on "Java Annotations"

  1. ramachandrareddy says:

    what is usages in real time senariao of annations

  2. harish says:

    which of the following keyword is used to create an user defined annotation?
    d)NOne of the above

    which of the following is used only in the case of Inheritance?
    a) @Depricated

  3. […] Configuration for dependency are done using Spring-configuration XML or using annotations. Annotations are mostly preferred for their ease of use. Spring manages these objects using BeanFactory. When an […]

  4. Siddique says:

    Please can you provide the annotation list on this email id..

    Thanking you

  5. Siddique says:

    Sir, We want annotation list .

  6. rajesh kumar mallick says:

    This is very clear and good presentative.somany things i got it aboput annotaion.

  7. kumar says:

    How can i get the field name while creating our own annotation?

  8. Michael Vino says:

    Such a wounderful articale

  9. Amir says:

    good and clear explanation… Would be great if Joe can answer the questions posted by viewers on the comments. I know it needs moretime, but found many unanswered.

  10. ajit says:

    Keep up the good work!

  11. Anonymous says:

    Thankyou Joe

  12. Piyush says:

    I enjoyed this reading . Thank you.

  13. Preeti Gupta says:

    Very informative, simple and easy to understand tutorial.. great work.. Keep it up joe..

  14. Joseph Kingston Leo M says:

    Thanks for Annotation KISS.(Keep it simple sir)

  15. Vijayagopal says:

    Very good presentation, go ahead….

  16. Mayumi says:


  17. Satish says:

    Hi Joe,

    First of all thanks a lot for presenting annotations in detail. It’s quite helpful

    But one thing I am very much eager to know is,

    Will it cause any issue if the annotations got compiled with one version of jdk (say jdk1.5) and the classes that use these annotations are complied with a different version of jdk (say jdk1.7) ?

  18. KAILASH says:

    Dear Joe,

    First of all thanks for the article.It’s really very useful. However i have one query. Are you sure that we can’t use parameters in methods?

    Because i have seen methods like following

    public String Joe(@RequestParam(“name”) String name, Model model)
    String message = “Hi” + name + “!”;
    model.addAttribute(“message”, message);
    return “Joe” ;

  19. Subhadeep Ray says:

    Rambo Mambo was good.

  20. Anonymous says:


    Its really good, after red this i impressed a lot, Thank you Joe for this Tremendous effort. Keep it up

  21. papiya says:

    ‘If the compiler finds that there is no matching method found in super class then generates a warning.’

    Please verify the above line under @Override.
    I think it creates compilation error…

    Anyways thanks for writing the blog.It was helpful.

  22. saravanan says:

    Superb explanation….thanks

  23. Venu says:

    Good Stuff …………

  24. anushri nayak says:

    Good one :)

  25. Venkat says:

    Nice Stuff

  26. Vairavel says:


  27. Arun K says:

    Hi Joe,

    All your articles are easy to understand. Thanks for such a explanation. I suggest you to describe further in detail where ever required.

    My question to you is:

    step 1) I have created Customize annotation

    public @interface ExecuteBeforeMethod{
    //Some attributes over here
    String methodName();
    String className();

    step 2) Creat Class where i use above annotation

    Class Test{
    @ExecuteBeforeMethod(className=”xyz”, methodName=”abc”)
    public method(){

    //Some logic over here

    But how does JVM comes to know at runtime to call method which i mentioned in my annotation? or How does dynamic binding of annotation and for method to which i written annotation is related to?

    Parsing i know and you written it in main() method in your example.

    But for my application how do i do?

    When my code call “method()” before that how method which i mentioned in annotation is called? or How and where parser is linked in this case?

  28. A Ray says:

    Replace ‘Annotation Types’ with ‘Meta Annotation Types’ in the heading under the ‘Meta Annotation’ section. Very well written nevertheless. Keep up the good work ! Appreciate it !

  29. sanchit says:

    very well organised tutorial, thanks

  30. Arun says:

    Very Nice article… Helpful to understand Annotations.

  31. moni says:

    anyone help me to know how to define values while creating annotation and how to call and compare that values in annotation

  32. Soumen Goswami says:

    Great discussion. Very Helpful. Thank You

  33. kabeer says:

    Hi , Great post
    Can you please tell how we can invoke methods also ,so that will get an idea how exactly JUnit ,TestNG
    If I am not wrong these tools work on Reflection and Annotation ?

  34. Explain Java says:

    Very clean explanation. Keep it up :)

  35. sandeep says:

    What is most important widely used design pattern in java?
    can u briefly explain? What is Observer design pattern?

  36. jaiganesh says:

    I believe that we can create annotations with Retention Policy SOURCE (or) CLASS.

    But I could not imagine the real time scenarios. If Retention Policy is CLASS, how can I instruct compiler to do particular task?
    If it’s SOURCE, can we create some applications like javadoc ?

  37. Enrico says:

    Very nice explanation. Good Work! Tks

  38. Pooja says:

    really helpful .. great work done

    by explaining so neatly .. thank U

  39. Pooja says:

    really helpful .. great work done

    by explaining so neatly .. thank U

  40. Sagar Deshmukh says:

    Nice explanation!
    One quick question.
    What if I want to have dynamic argument value in argument

    public @interface Developer {
    String merID();
    package com.javapapers.annotations;
    public class BuildHouse {

    @Developer (merID = merID)
    public void aliceMethod(String merID) {
    System.out.println(“This method is written by Alice”);


    here I want to set that argument ‘merID’ value to be the same as value of argument I’m passing in method ‘aliceMethod(String merID)’.

  41. Abhishek says:

    Hi Joe ,

    What i a trying to do is that

    Step 3: Create Axis2 Web Service

    I am trying to keep the server runtime and web services runtime same.
    As i dont have the axis client with me right now.

    I am using jboss for the same.
    for this purpose i have created there are two jboss folders i.e. one is the jboss and another is copy of it.

    I have given different paths for the server runtime and web server runtime.

    server runtime —-path of the jboss folder
    web server runtime —path of the copy of the jboss folder

    Now the issue is
    —>when i click on the next button
    —>check the option as Generate wsdl file
    —->and then again click on the next button.

    the error which i am getting is system can not find the path specified.

    I am still puzzled, which path the system is looking for.

    Can you pls guide.

    Abhishek J

  42. mandee says:

    The explanation on the topic here is the best as compared to other blogs. I would appreciate if you could explain “How to Parse Annotation” a bit more so that even a beginner can understand (actually i couldn’t understand what’s going on in the code).


  43. Shaffic says:

    Hi Joe,

    Thanks for giving glimpse on annotations :)

  44. Saidi says:

    Your blog has been very userful

  45. Abhay says:

    But what is the effect the Annotation can have on the method . i.e how the method is associated with Annotation.

    @interface myAnnotation1{
    public String name() default “Abhay”;
    public int age() default 35;


    class Annotated {

    public void foo(String myParam) {

    System.out.println(“This is ” + myParam);

    What effect the @myAnnotation is having on foo() and how can we access the values of @myAnnotation in foo() method..

  46. Loveleen Girdhar says:

    sir i m new in industry and in which company i m there is work of springs,hibernate. can u plz tell me from where should i read these things…

    Thanks in advance.

  47. csk says:

    explanation was good…

  48. Anonymous says:

    i m out of this field, bt i think sharing s so good, thanks,keep going!!!!

  49. sal says:

    can i create an annotation where i can use the logger



    class Test{“this is test method”);


    means i want to just add @Logger above the class,it will use the respective class name and LOGGER instance.

    how can i do the same



  50. Karan D Singh says:

    Beautiful Explanation.. Immaculate.

      • Anonymous says:

        teamId = 73,
        teamName = “Rambo Mambo”,
        teamLead = “Yo Man”,
        writeDate = “3/1/2012″

        in this case we will see same code in generated javadoc. I mean
        @Team(teamId=73,teamName=”Rambo Mambo”,…

        Is anyone knows how to put only values in javadoc. For exaple
        public @interface MyAnnotation {
        String description() default “none”;
        I need to put ONLY! String value of description.

  51. Karthik M says:

    Thanks for the good tutorial

  52. Rajesh Antony says:

    Great work Joe. This was an elusive topic but your narration hugged me to the topic and made me confident. Your Great attitude to share is appreciated.

  53. GopiNaidu says:

    Excellent Joe, It is very useful. Thanks

  54. Anonymous says:

    This is Suresh Arkati..
    Than q for u r Material….

  55. Anonymous says:

    I am not undestanding clearly.
    I want more explanation about annotations.

  56. Dev says:

    thanks a lot

  57. Anonymous says:

    Please write a tutorial on Spring annotations..

  58. kasinathan says:

    i didn’t get the clear idea about the @inherited

    i want more explanation

    For Example @Test class it has been inherit the properties of the class Test.How can i do that one.I need a One Example
    Thanks …..

  59. sanu says:


  60. Nandish says:

    Thanks for that wonderful tutorial

  61. Srinivas says:

    Hi, is there a way to remove annotation of a class runtime ?

  62. Udhay says:

    Why do we go for annotations? for ex: @Inherited used for inherit the super class to derived class. that can be done through the ‘extends keyword’ right?, then what is the need of Annotaions?

  63. Purush says:

    Hi Joe, Thanks for the nice explanation about basics on Annotation.

    Can you please clarify… is it possible to pass as annotation as Parameter to a method


  64. Thennam says:

    Hi Joe,

    Thanks for the wonderful information on annotations.

    It will be really helpful, if you provide the followings

    1. Advantage of annotations? How annotations helps the developers?

    2. When should we go for annotations?

    3. How the annotations affects the behavior of the class @ run-time? if yes, please explain.

  65. Shiv says:

    Joe you have mentioned that don’t use annotations for data base related things, but in hibernate annotations are used for mapping.

    Can you clarify my confusion?

  66. pooja says:

    Hi Joe – i have read almost all your articles..u explain every concept so well.. keep it up :)

    I have one very basic question for Annotation. I have googled this at so many places but not got satisfactory ans.

    Just i want to know
    b) Annotation is for JVM or for compiler or for other tools.
    c)If it is for some specific tool, where i define it.

    For eg i created any class for caching purpose and i made annotation for it like cacheable.. but what use of doing it.. M i really achieving anything?

    My question might sounds you little too basic or dumb but would appreciate if you will answer.

    Thanks in advance

  67. Mubarak Ali says:

    Good work. Thanks.

  68. Rahul Raj says:

    Mast Narrated Explanation bhai

  69. vijay says:

    Dear Joe, I am a newbie and I have become your fan. Whenever I google for some topics in Java and I see your picture, I go straight for your link.

    You explanations are simple and straight forward. Please keep up the good work.

    And thanks again!

  70. Karunanidhi says:

    Good introduction on annotations exactly what I looked for.

  71. Gilsha says:

    Great stuff Joe. Thanks

  72. Ajay K says:

    HI Joe, I found this article interesting, but somehow it seems good only for beginers. The part which i felt missing was much more technical part to the actual topic, which i found same in link:


  73. Durgasankar says:

    Good One Joe keep going……….

  74. Rajesh says:

    Simple and Super!!

  75. jvmlover says:

    Pretty good article!
    Keep going, your blog is great.

  76. Saurabh Prakash says:

    Great Stuff.Thanks

  77. Nageswara Rao Mothukuri says:

    Thanks. It’s very helpful for me after all searching through google, finally i got good note.

  78. Jicky says:

    multivalue annotation is not exmplained

  79. Giri Kanchukota says:

    Nice information to learn annotations

  80. Sajjan says:

    Very nicely compiled article. You should write tech books :) Thanks.

  81. Vysakh Suresh says:

    Thank you . . ;)

  82. Geekdude says:

    Given inDetailed Annotation explanations. Very very Thanks.

  83. swapnil gorane says:

    gr8 , thank you,
    it is very help full for me…

  84. kamesh duvvuri says:

    it’s amazing u r blog.I am first watch this blog it was good. wondonful

  85. sara says:

    great, keep going

  86. Kapil Suryawanshi says:

    Fantastic information. I didnt know what was this concept, but now I am comfortable to play with it.
    Thank you.

  87. krishnamurthy says:

    Good example Joe…..

  88. Anonymous says:

    Nice post Joe!

  89. Moove says:

    How abt including the Like button in the end of article…??

  90. Satheskumar says:

    Hi Joe. The things posted here are very much useful to everyone. Thanks..

  91. Suvasish says:

    really great!!!! keep up doing the good work for us..

  92. JavaPathshala says:

    Nice explaination

  93. Anonymous says:

    Cool stuff..great refresher ..


  94. S.Narayana Moorthi says:


    It was a great surprise to me seeing ur blog. Your learning is great!
    Your attitude to share it is greater!
    Sharing it in a way even a layman would understand is the greatest of all!
    Keep rocking. :)

  95. Praveen Kumar Jayaram says:

    Nice article.

  96. chandoo says:

    Joe, you are Excellent……….

  97. krishnamurthy says:

    Nice one Joe.It is very use full to me.

  98. chandrashekar says:

    Thaks .It is very useful for me

  99. Mario Guerrero says:


  100. Ajai G says:

    Very well narrated Annotation in detail. Specially to mention the Runtime Reflection example tops it all. Keep going..!!

Comments are closed.