Android create custom annotations

Question

I'm learning how to create own annotations. I have read this: http://www.mkyong.com/java/java-custom-annotations-example/ but I have to pass all classes with my annotation - thats bad. So I have read this: https://stackoverflow.com/a/7665191/3279023 Unfortunately it throws an exception:

java.lang.NoSuchFieldException: No field mDexs in class Ldalvik/system/PathClassLoader; (declaration of 'dalvik.system.PathClassLoader' appears in /system/framework/core-libart.jar)

basicly:

Failed to get mDexs field

My goal:

I want to create custom annotation Permission - and i did:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Permission {
    String value() default "none";
}

Now, every time method with this annotation is run I want to check some conditions conditions and decide if method should be running... like:

@Permission(value = "testValue")
private void foo() {
    // do stuff if permission allows
}

Why i want to do that? I think it will be good replacement for if statements:

private void foo() {
    if(MyFooClass.STATIC_BOOLEAN_FIELD)
       // do stuff
}

I have a lot of that if statement in my project and I want to get rid of it somehow

Is that even possible? And safe? And good idea?

Answer 1

I'm not sure it is a good idea, at least in terms of performance... But if you really want to do it, you just need reflection.

public void foo() {
    Class<?> c = this.getClass(); // get the class object
    Method m = c.getDeclaredMethod("foo"); // get the method
    Permission p = m.getAnnotation(Permission.class); // get annotation
    if (p!=null && p.value().equals("testValue") {
        // do your test
    }
    else {
        // do what you want 
    }
}

If you need to do this many times, you may use a static method boolean isAnnotated(String methodName) for example. So that you just have to write a preamble in each concerned method : if (isAnnotated("foo")) {} else {}