How to create custom annotation in java : Step by step explanation

Before discussing  how to create a custom annotation in java , we have already shared  java annotations tutorials for beginners  . Sometimes in our web services we need to create custom annotation . So let us understand the term annotation first before discussing custom annotation . Annotation is a kind of meta data , in other words ,it represents data about data .

The great myth behind why @ symbol was chosen for annotations.
@: AT: Annotation Type


Read Also :      Java Annotation tutorials for beginners

                         Top 10 most frequently used Annotation  Examples
    

 

Java annotation can be useful to provide property of class or object .There are 3 steps involved in creating custom annotation .Below are the steps  to create custom annotation in java along with example.

Step 1 

Create an annotation with the following code in MySampleAnnotation.java

package com.sample.annotation;

public @interface MySampleAnnotation //@ symbolizing that this is an Annotation
                                       Type

{ 
    public String name();   // The scope here matches with the conventions

                               followed for an interface. Default is public

                               and that’s the only allowed modifier
    public int age();       // The scope here matches with the conventions

                               followed for an interface. Default is public

                               and that’s the only allowed modifier   
}

The annotation type has all the features equal to that of an interface, exceptions are
1) Specifying @ symbol before interface keyword
2) Allowing of default values to its method


Step 2

Create a client class that uses the above created annotation, as below,

package com.sample.annotation;

public class MySampleAnnotationClient {
    public static void main(String args[]) {
        MySampleAnnotationClient mySampleAnnotationClient =                    
                                      new   MySampleAnnotationClient(); 

        mySampleAnnotationClient.myMethod();  
    }
    
    @MySampleAnnotation(name = "Sreenivasan Arumugam", age = 29) 

      //We give the values to the attributes

        of an annotation as a comma-separated values

 public void myMethod() {
        System.out.println("Alive is awesome");
    }
}

Step 3

Compile and execute the above program, you should get the output as below,

      

Alive is awesome

Cheers !!! you have created your first annotation .