What is super" keyword in Java?
Tags: java
Published: 2023-11-23 07:53:52

Java annotations are a form of metadata that provide information about the structure, behavior, or attributes of program elements in Java code. Annotations are introduced in Java 5 and have since become an integral part of the Java language. They allow developers to embed additional information, or metadata, within the source code, which can be processed by tools, frameworks, or the Java runtime environment. Annotations are typically denoted with the @ symbol followed by the annotation type name. Apart from it by obtaining [Java Training](https://www.edureka.co/java-j2ee-training-course), you can advance your career in Java. With this course, you can demonstrate your expertise in Core Java & J2EE basic and advanced concepts and popular frameworks like Hibernate, Spring & SOA, many more fundamental concepts, and many more.


**Here are some key points about Java annotations:**

Syntax: Annotations are defined using the @ symbol followed by the annotation type name. They can also include elements with values, similar to methods with default values.

java
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@AnnotationType
public class MyClass {
    @AnnotationType("someValue")
    private String myField;

    @AnnotationType(value = 42)
    public void myMethod() {
        // Method implementation
    }
}
Built-in Annotations: Java provides several built-in annotations, such as @Override, @Deprecated, and @SuppressWarnings. These annotations serve various purposes, like indicating that a method is intended to override a superclass method, marking a method as deprecated, or suppressing compiler warnings.

Custom Annotations: Developers can define their custom annotations using the @interface keyword. Custom annotations can be used to provide additional information specific to their applications or frameworks.

java
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@interface MyCustomAnnotation {
    String value() default "default value";
    int count() default 0;
}
Annotation Processors: Annotations are often processed by tools and frameworks to generate code, configure behavior, or perform other tasks. For example, Java's built-in annotations like @Entity and @Table are used in Java Persistence API (JPA) to define database mappings, and frameworks like Spring use annotations to configure beans and manage dependencies.

Retention Policy: Annotations can have different retention policies, specifying how long the annotation's information should be retained. Java supports three retention policies:

SOURCE: Annotations are only available in the source code and are not included in the compiled bytecode.
CLASS: Annotations are included in the compiled bytecode but are not available at runtime.
RUNTIME: Annotations are included in the compiled bytecode and are available at runtime through reflection.
Annotation Targets: Annotations can be applied to various program elements, including classes, fields, methods, parameters, and more. The allowed targets are defined by the annotation type's @Target meta-annotation.

java
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@Target({ElementType.TYPE, ElementType.METHOD, ElementType.FIELD})
@interface MyAnnotation {
    // Annotation elements
}
Annotations as Markers: Annotations are often used as markers to indicate the presence of certain features or behaviors. For example, the @Serializable annotation can indicate that a class can be serialized, and the @Controller annotation in the Spring framework marks classes as controllers.

Metadata Generation: Annotations can be used to generate metadata that can be processed at compile-time or runtime. For example, frameworks like Hibernate use annotations to generate database schema definitions from annotated Java classes.

In summary, Java annotations are a powerful and flexible mechanism for adding metadata to Java code. They play a crucial role in simplifying configuration, improving code readability, and enabling code generation and customization in various Java applications and frameworks. Developers can use built-in annotations or create custom annotations to enhance their code and interact with tools and libraries more effectively.