annotations
DESCRIPTION
Brief introduction of Annotations a new features introduced with java1.5 & enhanced with java1.6. Very handy ppt to understand the concept of annotation with simple & pictorial examples. Annotations are the wild use features by framework builders like spring, hibernate. Read it once & build a better understanding of java annotations.TRANSCRIPT
Annotation Jdk1.6
Pawan Modi Senior R&D Engineer
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Agenda
• Introduction• First Example• Defining Annotations• Annotations Types & Usage• Example• Summary
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Introduction
Annotations are generally a way to add meta-data information to an element.
An annotation type definition takes an "at" (@) sign, followed by the interface keyword plus the annotation name.
An element can be a class, method, field, constructor, variables etc.
This meta-data are processed by the tools i.e. compilers, javadoc, etc.
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First Example
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Defining Annotation Some rules to define an annotation type Annotation declaration should start with an 'at' sign like
@, following with an interface keyword, following with the annotation name.
Method declarations should not have any parameters. Method declarations should not have any throws
clauses. Return types of the method should be one of the
following: primitives String Class enum array of the above types
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Annotation Types There are two types of annotations available in JDK5◦ Simple annotations: Just to annotate your code. Developer cannot use them to create a custom annotation type. There are only three types of simple annotations provided by JDK5 Override Deprecated Suppresswarnings
◦ Meta annotations: These are the annotation types designed for annotating annotation-
type declarations. Simply speaking, these are called the annotations-of-annotations.
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Simple AnnotationsOverride ◦ This annotation tells compiler that method
must be an overridden method.
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Simple Annotations Conti…
Deprecated ◦ This annotation informs client not to use this
method / class anymore because in the future versions this old method / class may not be supported. ◦ Clients may prepare themselves not to
depend on the old method anymore.
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Simple Annotations Conti…
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Simple Annotations Conti…
SuppressWarnings ◦ From Java 5.0, references to any of the
Collection types should be parameterized. Else the compiler will issue a warning message. The solution for this problem is to make use of @SuppressWarnings annotation.
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Simple Annotations Conti…
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Annotation Types Conti…
Meta annotations: ◦ These are the annotation types designed for
annotating annotation-type declarations. Simply speaking, these are called the annotations-of-annotations. ◦ There are four types of meta-annotations. Target Retention Documented Inherited
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Meta Annotations Target
tells for which element type this annotation is applicable It contains the following enumerated types as its value: @Target(ElementType.TYPE)—can be applied to any element of a
class @Target(ElementType.FIELD)—can be applied to a field or property @Target(ElementType.METHOD)—can be applied to a method level
annotation @Target(ElementType.PARAMETER)—can be applied to the
parameters of a method @Target(ElementType.CONSTRUCTOR)—can be applied to
constructors @Target(ElementType.LOCAL_VARIABLE)—can be applied to local
variables @Target(ElementType.ANNOTATION_TYPE)—indicates that the
declared type itself is an annotation type
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Meta Annotations Conti . . .
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Meta Annotations Conti…Retention Tells what extent the Annotations should be
retained. The three possible ways of telling this are, RetentionPolicy.SOURCE—Annotations with this type will
be by retained only at the source level and will be ignored by the compiler
RetentionPolicy.CLASS—Annotations with this type will be by retained by the compiler at compile time, but will be ignored by the VM
RetentionPolicy.RUNTIME—Annotations with this type will be retained by the VM so they can be read only at run-time
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Meta Annotations Conti…
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Meta Annotations Conti…Document◦ indicates that an annotation with this type
should be documented by the javadoc tool ◦ By default, annotations are not included in
javadoc ◦ But if @Documented is used, it then will be
processed by javadoc-like tools and the annotation type information will also be included in the generated document.
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Meta Annotations Conti…
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Meta Annotations Conti…Inherited◦ It indicates that the annotated class with this
type is automatically inherited. ◦ if you define an annotation with the
@Inherited tag, then annotate a class with your annotation, and finally extend the class in a subclass. ◦ All properties of the parent class will be
inherited into its subclass
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Meta Annotations Conti…
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Example
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Example
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Example Conti…
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Summary Annotation is a special form of syntactic metadata
that can be added to Java source code.
They provide information about various elements of a Java class.
Classes, methods, variables, parameters and packages may be annotated.
There are seven annotations provided in the J2SE 5.0 release. @Deprecated, @Override, @SuppressWarnings,
@Documented, @Inherited, @Retention and @Target.
These are not data about data but data about classes, methods, instance and static variables etc
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ReferencesOnline Tutorial
http://en.wikipedia.org/wiki/Java_annotation http://www.javabeat.net/articles/30-annotations-
in-java-50-1.html http://www.developer.com/java/other/article.php/
10936_3556176_1 http://java.sun.com/j2se/1.5.0/docs/guide/language/
annotations.html
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Question ??
Kindly send all you queries to the following id.
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Thank you!
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