Annotations in Java
The Annotations in Java are a form of the metadata that can be added to Java code to provide information about the code to compiler and runtime environment.
- Built-in Annotations: These are the annotations provided by Java, such as, @Override, @Deprecated and @SuppressWarnings.
- Custom Annotations: To Creating custom annotations to add metadata to our own code.
- Annotation Processors: The Processing annotations at compile time to generate additional code or perform specific tasks.
Use Cases:
- Code Organization: Adding information about code’s intended use, relationships or constraints.
- Frameworks and Libraries: The Many Java frameworks use annotations for the configuration and behavior customization.
- Documentation: The Generating documentation or providing hints to the tools and IDEs.
Example:
Java
//Java program to demonstrate Annotations import java.io.*; import java.lang.annotation.*; @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface CustomAnnotation { String value() default "The Default Value"; } public class AnnotationExample { @CustomAnnotation("The Custom Value") public void annotatedMethod() { // Method implementation } } |
Explanation of the Program:
- The above Java program defines a custom annotation with the retention policy RUNTIME and Target Element type METHOD.
- It then applies this annotation to the method in the AnnotationExample class.
- When executed, the output is not explicitly visible in the code, but program demonstrates how to use annotations.
- The Annotations themselves don’t produce output when the program runs.
Deep Dive into Java Reflection and Annotations
The Java Reflection and Annotations are powerful features that provide dynamic and metadata-driven capabilities to Java applications. The Reflection allows the examination and manipulation of the class properties, methods, and fields at runtime while Annotations provide a way to add metadata and behavior to the code.