Question

Guys is there a way to pass a Annotation as a direct parameter (rather by doing all the reflection overhead)? For example in the following code, I have a annotation Number that holds a int value, I want to pass as a parameter to the addImpl method, how can I do that (other than by reflection)?

Code Snippet:

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD})
public @interface Number {
    int value();
}

public void add(int x2) {
    addImpl(@Number(value = 10) lol, x2);
}

public void addImpl(Number a, int b) {
    System.out.println(a.value() + b);
}

public static void main(String[] args) {
    new TestClass().add(3);
}

Answer 1

Yes, you can pass around annotations like this (just as if they were normal interfaces).

The only thing you can’t do is to create instances of that interface at runtime. You can only take existing annotations and pass them around.

import java.lang.annotation.*;

public class Example {

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.METHOD)
    public static @interface Number {
        int value();
    }

    @Number(value = 42)
    public int adder(final int b) throws SecurityException, NoSuchMethodException {
        Number number = getClass().getMethod("adder", int.class).getAnnotation(Number.class);
        return addImpl(number, b);
    }

    public int addImpl(final Number a, final int b) {
        return a.value() + b;
    }

    public static void main(final String[] args) throws SecurityException, NoSuchMethodException {
        System.out.println(new Example().adder(0));
    }
}