Java Annotations

🏷️ Java Annotations

Annotations in Java are metadata that provide information about the code to the compiler or runtime environment.

Do not change program semantics directly
Help in compile-time checking, documentation, and runtime processing
Package: java.lang.annotation (for custom annotations)

1. Why Use Annotations?

Compile-Time Checking – Helps compiler detect errors.
Code Documentation – Provides extra information.
Runtime Processing – Frameworks like Spring, Hibernate, and JUnit use annotations.

2. Built-in Annotations in Java

Annotation	Description
`@Override`	Checks if a method overrides a superclass method
`@Deprecated`	Marks a method/class as outdated
`@SuppressWarnings`	Suppresses compiler warnings
`@FunctionalInterface`	Marks an interface as functional (for lambdas)
`@SafeVarargs`	Suppresses warnings for variable arguments (varargs)

Example: `@Override`

class Parent {
void display() {
System.out.println("Parent display");
}
}class Child extends Parent {
@Override
void display() {
System.out.println("Child display");
}
}

public class OverrideExample {
public static void main(String[] args) {
Parent obj = new Child();
obj.display(); // Output: Child display
}
}

class Parent {

void display() {

System.out.println("Parent display");

}

}class Child extends Parent {

@Override

void display() {

System.out.println("Child display");

}

public class OverrideExample {

public static void main(String[] args) {

Parent obj = new Child();

obj.display(); // Output: Child display

}

@Override ensures compile-time checking.
If method name is wrong, compiler will show an error.

Example: `@Deprecated`

class OldClass {
@Deprecated
void oldMethod() {
System.out.println("This method is deprecated!");
}
}public class DeprecatedExample {
public static void main(String[] args) {
OldClass obj = new OldClass();
obj.oldMethod(); // Compiler will show a warning
}
}

class OldClass {

@Deprecated

void oldMethod() {

System.out.println("This method is deprecated!");

}

}public class DeprecatedExample {

public static void main(String[] args) {

OldClass obj = new OldClass();

obj.oldMethod(); // Compiler will show a warning

}

Warns developers not to use old methods.

Example: `@SuppressWarnings`

Suppresses specific compiler warnings.

3. Custom Annotations

You can create your own annotations using @interface.

import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME) // Available at runtime
@Target(ElementType.METHOD) // Can be applied to methods
@interface MyAnnotation {
String author();
String date();
}

class Demo {
@MyAnnotation(author = "Vipul", date = "2025-12-08")
public void myMethod() {
System.out.println("This method has a custom annotation");
}
}

public class CustomAnnotationExample {
public static void main(String[] args) throws Exception {
Demo obj = new Demo();
obj.myMethod();

// Access annotation via reflection
MyAnnotation ann = obj.getClass().getMethod("myMethod").getAnnotation(MyAnnotation.class);
System.out.println("Author: " + ann.author());
System.out.println("Date: " + ann.date());
}
}

import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME) // Available at runtime

@Target(ElementType.METHOD) // Can be applied to methods

@interface MyAnnotation {

String author();

String date();

}

class Demo {

@MyAnnotation(author = "Vipul", date = "2025-12-08")

public void myMethod() {

System.out.println("This method has a custom annotation");

}

public class CustomAnnotationExample {

public static void main(String[] args) throws Exception {

Demo obj = new Demo();

obj.myMethod();

// Access annotation via reflection

MyAnnotation ann = obj.getClass().getMethod("myMethod").getAnnotation(MyAnnotation.class);

System.out.println("Author: " + ann.author());

System.out.println("Date: " + ann.date());

}

@Retention(RetentionPolicy.RUNTIME) → Available at runtime
@Target(ElementType.METHOD) → Specifies applicable targets (methods, classes, fields, etc.)

4. Meta-Annotations

Annotations that describe other annotations:

Meta-Annotation	Description
`@Retention`	How long annotation is retained (SOURCE, CLASS, RUNTIME)
`@Target`	Where annotation can be applied (METHOD, FIELD, TYPE, etc.)
`@Documented`	Include annotation in Javadoc
`@Inherited`	Allows annotation to be inherited by subclasses

Summary

Annotations = Metadata for code
Types: Built-in (@Override, @Deprecated) and Custom
Meta-Annotations control behavior of annotations
Used in compile-time checking, documentation, and runtime frameworks

Java Annotations

🏷️ Java Annotations

1. Why Use Annotations?

2. Built-in Annotations in Java

Example: @Override

Example: @Deprecated

Example: @SuppressWarnings

3. Custom Annotations

4. Meta-Annotations

Summary

You may also like...

Java Interface

Java Create Files

Java Date and Time

Example: `@Override`

Example: `@Deprecated`

Example: `@SuppressWarnings`