? Java Custom Annotations

? Quick Overview

Custom annotations in Java allow developers to define their own metadata that can be attached to classes, methods, fields, parameters, or other program elements. These annotations are widely used for configuration, documentation, validation, and framework-level processing.

? Key Concepts

• Annotations are metadata, not executable code
• Custom annotations are created using @interface
• Annotations can have elements (methods without bodies)
• Retention policy controls availability at runtime
• Target defines where the annotation can be applied

? Syntax & Theory

A custom annotation is declared using the @interface keyword. You can control its behavior using meta-annotations such as @Retention and @Target.

// Custom annotation definition
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.annotation.ElementType;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface MyAnnotation {
String value();
int count() default 1;
}

? Code Example(s)

// Using the custom annotation on a method
public class Demo {

@MyAnnotation(value = "Test Method", count = 3)
public void show() {
System.out.println("Hello from annotated method");
}
}

? Live Output / Explanation