Java - Alternatives to forcing subclass to have a static method

Question

I often find I want to do something like this:

class Foo{
public static abstract String getParam();
}

To force a subclasses of Foo to retur

Answer 1

The best you can do here in a static context is something like one of the following:

a. Have a method you specifically look for, but is not part of any contract (and therefore you can't enforce anyone to implement) and look for that at runtime:

 public static String getParam() { ... };
 try {
     Method m = clazz.getDeclaredMethod("getParam");
     String param = (String) m.invoke(null);
 }
 catch (NoSuchMethodException e) {
   // handle this error
 }

b. Use an annotation, which suffers from the same issue in that you can't force people to put it on their classes.

@Target({TYPE})
@Retention(RUNTIME)
public @interface Param {
   String value() default "";
}

@Param("foo")
public class MyClass { ... }


public static String getParam(Class clazz) {
   if (clazz.isAnnotationPresent(Param.class)) {
      return clazz.getAnnotation(Param.class).value();
   }
   else {
      // what to do if there is no annotation
   }
}