Working with Annotations in Java

Question

Ravi Vishwakarma · Answer

Annotations in Java are a form of metadata. They provide data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate but are widely used in frameworks (like
Spring, JUnit) for configuration and behavior control.
1. Built-in Annotations
Java provides several built-in annotations, such as:
@Override – Ensures that a method is overriding a superclass method.@Deprecated – Marks a method/class as deprecated (shouldn’t be used).@SuppressWarnings – Tells the compiler to ignore specific warnings.
public class Example {
    @Override
    public String toString() {
        return "Example";
    }
    @Deprecated
    public void oldMethod() {
        System.out.println("This method is deprecated");
    }
}
2. Creating Custom Annotations
You can define your own annotation using @interface.
Example:
import java.lang.annotation.*;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface MyAnnotation {
    String value() default "Default value";
}
@Retention – Specifies how long the annotation is retained (e.g.,
SOURCE, CLASS, RUNTIME).@Target – Indicates where this annotation can be used (e.g., 
METHOD, FIELD, TYPE).
3. Using Custom Annotation
public class TestAnnotationUsage {
    @MyAnnotation(value = "Hello Reflection")
    public void testMethod() {
        System.out.println("Running testMethod");
    }
}
4. Accessing Annotations with Reflection
You can use reflection to read and process annotations at runtime.
import java.lang.reflect.Method;
public class AnnotationProcessor {
    public static void main(String[] args) throws Exception {
        Classandlt;?andgt; clazz = TestAnnotationUsage.class;
        for (Method method : clazz.getDeclaredMethods()) {
            if (method.isAnnotationPresent(MyAnnotation.class)) {
                MyAnnotation annotation = method.getAnnotation(MyAnnotation.class);
                System.out.println("Method: " + method.getName());
                System.out.println("Annotation value: " + annotation.value());
            }
        }
    }
}
5. Common Framework Use Cases
Spring Framework uses annotations like @Autowired,
@Service, @Controller, @RequestMapping.JUnit uses @Test, @BeforeEach, 
@AfterEach.Hibernate uses @Entity, @Table, 
@Column.
Summary Table
Concept
Usage
@interface
Declares a custom annotation
@Retention
Defines how long the annotation is kept
@Target
Defines where the annotation can be applied
Reflection
Used to read annotations at runtime
and

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Working with Annotations in Java

Ravi Vishwakarma

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1 Answers

1. Built-in Annotations

2. Creating Custom Annotations

Example:

3. Using Custom Annotation

4. Accessing Annotations with Reflection

5. Common Framework Use Cases

Summary Table

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Concept	Usage
`@interface`	Declares a custom annotation
`@Retention`	Defines how long the annotation is kept
`@Target`	Defines where the annotation can be applied
Reflection	Used to read annotations at runtime