What are annotations in Java? How are they used?

Question

Ravi Vishwakarma · Answer

Annotations in Java are a form of metadata that can be added to Java code (classes, methods, variables, etc.). They provide information to the compiler and can be used at runtime by the JVM or other tools for various purposes.

Types of Annotations

Standard Annotations: Java provides several built-in annotations in the java.lang package.

@Override: Indicates that a method is overriding a method in a superclass.
@Deprecated: Marks a method or class as deprecated, meaning it should not be used.
@SuppressWarnings: Tells the compiler to suppress specific warnings.

public class MyClass {
    @Override
    public String toString() {
        return "MyClass";
    }

    @Deprecated
    public void oldMethod() {
        // Do something
    }

    @SuppressWarnings("unchecked")
    public void myMethod() {
        // Do something
    }
}

Meta-Annotations: Meta-annotations are annotations that apply to other annotations. Some of the meta-annotations are:

@Retention: Specifies how long the annotation is retained (runtime, class file, source).
@Target: Specifies the kinds of elements an annotation type applies to (methods, fields, classes).
@Documented: Indicates that an annotation should be documented by Javadoc and similar tools.
@Inherited: Indicates that an annotation type is automatically inherited.

Example:

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

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What are annotations in Java? How are they used?

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Types of Annotations