Thursday, June 5, 2014

How to create/declare and use annotations in Java - Part 1

8:55 PM | Posted by | | Edit Post
Today in this article I will show you how to create your own annotation. Here we will start with a very basic annotation and then slowly show you how to include arrays and also how to use default values. We will also show you how to yo use annotations. We have divided our tutorial on creating and using annotations in two parts. The first part meaning this one is a very basic and good one for beginners to start with.
In our first annotation we will just start with an empty annotation specifying only @target and @Retention.
import java.lang.annotation.*;

@Target(value={ElementType.FIELD})
@Retention(value=RetentionPolicy.RUNTIME)
public @interface Author {
}
In the next example you will see that when there is only one value for an annotation then we can omit the name as well as braces{} indicating arrays. The above sample is re-written as
import java.lang.annotation.*;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Author {
}
In our next example you will see how to mention the target type when it is more than one say FIELD and METHOD.
import java.lang.annotation.*;

@Target({ElementType.FIELD, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Author {
}
In our next example we will deal with annotation which has annotation type elements. It looks almost like methods. We will also show you how to use this annotation in a class.
import java.lang.annotation.*;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Author {
 String name();
}

class MyClass {
 @Author(name="Nirupam")
 int i = 10;
}
In our next and last example of today, we will show you how to mention default values of annotation type elements. It is done using keyword default . If a default value is mentioned, then you can omit adding your own value. But it does not mean that you cannot add your own value, of course you can do it.
import java.lang.annotation.*;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Author {
 String name() default "Nirupam";
}

class MyClass {
 @Author
 int i = 10;
}
In our next and last part we will deal with creating and using advanced annotation. Till then keep coding and keep reading our articles.
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