Custom Annotation

A runtime annotation stores small metadata that reflection can read later.

CustomAnnotation.java

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

@Retention(RetentionPolicy.RUNTIME)
@interface Lesson {
    String name();
    int level();
}

@Lesson(name = "reflection", level = 2)
class AnnotatedExample {
}

public class CustomAnnotation {
    public static void main(String[] args) {
        int bonus = ;
        Lesson lesson = AnnotatedExample.class.getAnnotation(Lesson.class);
        int adjustedLevel = lesson.level() + bonus;

        System.out.println("name=" + lesson.name());
        System.out.println("level=" + adjustedLevel);
    }
}

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

@Retention(RetentionPolicy.RUNTIME)
@interface Lesson {
    String name();
    int level();
}

@Lesson(name = "reflection", level = 2)
class AnnotatedExample {
}

public class CustomAnnotation {
    public static void main(String[] args) {
        int bonus = ;
        Lesson lesson = AnnotatedExample.class.getAnnotation(Lesson.class);
        int adjustedLevel = lesson.level() + bonus;

        System.out.println("name=" + lesson.name());
        System.out.println("level=" + adjustedLevel);
    }
}

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

@Retention(RetentionPolicy.RUNTIME)
@interface Lesson {
    String name();
    int level();
}

@Lesson(name = "reflection", level = 2)
class AnnotatedExample {
}

public class CustomAnnotation {
    public static void main(String[] args) {
        int bonus = ;
        Lesson lesson = AnnotatedExample.class.getAnnotation(Lesson.class);
        int adjustedLevel = lesson.level() + bonus;

        System.out.println("name=" + lesson.name());
        System.out.println("level=" + adjustedLevel);
    }
}

annotation type An annotation type declares the metadata fields that can be attached to a program element.

runtime retention Runtime retention keeps annotation metadata available to reflection while the program runs.