Annotation Types in Java

December 6, 2022

Types of Annotation in Java

In order to add or add-on program information we use Annotations Types in Java. The language uses annotations to provide more information about the program.

These annotations are the tags that are attached to classes, interfaces, methods, and fields to designate extra information that the Java compiler and Java Virtual Machine may use. It is an alternative to XML (Extensible Markup Language ) and Java marker interfaces since Annotations types in Java are used to offer more information.

Annotations in Java

Annotations can be used to add extra details about a program.

It begins with – “@.”
They do not affect how a built program behaves.
Instance variables, constructors, methods, classes, and other program elements can all be annotated to add metadata (information).
As they can alter how a program is handled by the compiler, annotations are not simply comments. See the code example below.
An alternative to XML and Java marker interfaces, annotations are essentially used to provide extra information.

Where can Java Annotations be used? Classes, interfaces, methods, and fields can all be annotated.

Predefined Types of Java Annotations

There are seven built-in annotations in Java.

The four imported from java.lang.annotation

@Retention, @Documented, @Target, and @Inherited

Retention

Documented

Target

Inherited

Retention

To what level an annotation will be visible is specified using the @Retention annotation.

Annotation for @Retention It establishes the location and duration of the annotation’s retention. The @Retention annotation has three possible values:

SOURCE: The compiler will not take into account annotations; they will remain at the source level.
CLASS: The JVM ignores annotations, but they are kept at build time.
RUNTIME: At runtime, these will be kept.

Its syntax is:

@Retention(RetentionPolicy)

Documented

A tool is informed by a marker interface that an annotation has to be documented. Javadoc comments do not contain annotations. By using the @Documented annotation in the code, tools like Javadoc may process it and add information about the annotation type in the document that is produced.

For example,

@Documented
public @interface MyCustomAnnotation{ ... }

Target

It is meant to be used just as a justification for another annotation. One argument, which must match the ElementType count, is required for @Target.
The type of assertions that Java annotations can connect to are determined by this annotation. The constants are listed below with the category of affirmation that each one relates to.

Target constant	Annotations can be applied to
ElementType.ANNOTATION TYPE	An annotation type may be assigned to using
ElementType.CONSTRUCTOR.	Using a function Object() { [native code] } may be treated.
ElementType.FIELD.	A field or property can be used
ElementType.LOCAL VARIABLE	A local variable may be treated
ElementType.METHOD.	A method-level annotation
ElementType.PACKAGE	A package declaration can use this keyword
ElementType.PARAMETER.	The parameters of a method can be changed
ElementType.TYPE.	Any element of a class can be affected

Inherited

The marker annotation @Inherited can only be used on the annotation declaration. Only annotations used in class definitions are impacted. The superclass’s annotation is passed down to the subclass via the @Inherited annotation.

As a result, if a subclass is asked for a specific annotation and that annotation is missing from the subclass, the superclass is checked. It yields that annotation if both it and the @Inherited annotation are present in the superclass.

Its syntax is:

@Inherited

The three in java.lang

@Deprecated, @Override, and @SuppressWarnings

Deprecated

Override

SuppressWarnings

Deprecated

A marker annotation, that is. It signifies that a statement has been superseded by a newer form and is no longer valid.
When an element has been deprecated, the Javadoc @deprecated tag should be used.
Both the @deprecated tag and the @Deprecated annotation are used for runtime reflection.
When both are used, the @deprecated tag gets priority over the @Deprecated annotation.

The syntax is

@Deprecated
accessModifier returnType deprecatedMethodName() { ... }

Override

SuppressWarnings

The compiler is instructed to suppress certain compiler warnings using this information.
The names of the warnings to suppress are given in string form. Any declaration type may use this kind of annotation.
Java divides warnings into two groups. They are unchecked and deprecated.
When a legacy code interacts with a generics-using code, any unchecked warning is generated.

To suppress a particular category of warning, we use:

@SuppressWarnings("warningCategory")

For example,

@SuppressWarnings("deprecated")

To suppress multiple categories of warnings, we use:

@SuppressWarnings({"warningCategory1", "warningCategory2"})

For example,

@SuppressWarnings({"deprecated", "unchecked"})

Example Code for @Deprecated method

Run

import java.util.*;

public class Main{
  // We're in the deprecated method which is replaced by the newMethod()
  @Deprecated
  public static void PrepInsta(){ 
    System.out.println("I'm in Deprecated method of PrepInsta");
  } 

  public static void main(String args[]) {
    PrepInsta();
  }
}

Output:

I'm in Deprecated method of PrepInsta

Categories of Annotations Types in Java

There are generally 5 types of annotations.

Full Annotations They have numerous values, pairs, data members, etc. in them.

Marker Annotations The sole intent is to signify a proclamation. These annotations are empty and lack any members or data. Therefore, the fact that it is an annotation is sufficient. Since the marker interface doesn't have any members, it's sufficient to know whether it's present or not.

Repeating Annotations These are the annotations that may be used many times on a single item. The repeated annotation's container type is specified in its value field. The container is supplied as an annotation with a repeated array in the value field. As a result, to construct a repeated annotation, first create the container annotation, and then pass the annotation type as an argument to the @Repeatable annotation.

Type Annotations Anywhere that a type is used, these annotations can be included. We may annotate a method's return type, for instance.

Single value Annotations These annotations have just one member and let you specify the member's value in a concise manner. When the annotation is applied, we simply need to give the member's value; the name of the member is not necessary. However, the member's name must be a value in order to use this shortcut.

What use do Java Annotations serve?

Arrays: 1D and 2D

Methods

Abstract-classes-methods

Annotations in Java

Autoboxing-Unboxing in Java

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Instructions for the compiler To direct the compiler, we can use Java's built-in annotation feature. For instance, you can tell the compiler that a method is being overridden by another method by using the @override annotation.

Compilation-time teachers Annotations give the compiler compile-time instructions that we can later utilise with software development tools to create XML files, code, and other things.

Runtime guidance Annotations can be defined to be accessible at runtime and to be accessed through Java reflection.

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Annotation Types in Java

Types of Annotation in Java

Annotations in Java

Predefined Types of Java Annotations

Example Code for @Deprecated method

Categories of Annotations Types in Java

What use do Java Annotations serve?

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