分配对从超类覆盖的方法的较弱访问

Question

I have a Class called Module which has a Method onEnable(); Now i have a class called Config and want to make the onEnable(); method private because there is a predefined acting and a class extending Config should'nt be allowed to change the behaviour.

Is there any way to do this?

Example

class Module{

     public void onEnable(){

     }
}

A class extending Module which is allowed to use onEnable :

class HelloWorldModule{

     @Override
     public void onEnable(){

          System.out.println("Hello, World!");

     }


}

Now the config Class, where i want that onEnable is private so that Classes which extend Config cannot! Override onEnable :

class Config{

    @Override
    private void onEnable(){
    }


}

So NOW, a class named ProgrammConfig which extends Config cannot override onEnable .

However, this is not working because you cannot override a public method to a private method.

Answer 1

By declaring a method as public , you are saying that it should be possible to call said method on every instance of this class, including subclasses. Declaring a method as private in a subclass doesn't make sense, and is thus not allowed.

Now, if you're concerned about subclasses overriding the method, you can declare the method as final to prevent this:

class Config extends Module{

    @Override
    public final void onEnable(){}
        //Whatever
    }

Answer 2

You cannot solve this using inheritance. If Config is a subclass of Module , then it must provide all functions of Module with (at most) the same access restrictions. Think of a subclass as a specialized version of the superclass: It can do everything the superclass can, likely more, but never less.

Still you can implement a Config class as desired. Just skip subclassing, and instead use a private field of type Module like so:

class Config {
    private Module module;

    public Config() {
        module = new Module();
    }

    public int SomeFunctionFromModuleYouWantToExpose() {
        return module.SomeFunctionFromModuleYouWantToExpose();
    }

    // ...
}