Any way to force classes to have public static final field in Java?

Question

Is there a way to force classes in Java to have public static final field (through interface or abstract class)? Or at least just a public field?

I need to make sure somehow that a group of classes have

public static final String TYPE = "...";

in them.

Answer 1

No, you can't.

You can only force them to have a non-static getter method, which would return the appropriate value for each subclass:

public abstract String getType();

If you need to map each subclass of something to a value, without the need to instantiate it, you can create a public static Map<Class<?>, String> types; somewhere, populate it statically with all the classes and their types, and obtain the type by calling TypesHolder.types.get(SomeClass.class)

Answer 2

You can define an interface like this:

interface X {
   public static final String TYPE = "...";
}

and you can make classes implement that interface which will then have that field with the same value declared in the interface. Note that this practice is called the Constant interface anti-pattern.

If you want classes to have different values then you can define a function in the interface like this:

interface X {
   public String getType();
}

and implementing classes will have to implement the function which can return different values as needed.

Note: This works similarly with abstract classes as well.