Javaで幽霊型しようとした記録ですー＞ω＜

Callback.java

package com.github.kagamilove0707.safelist;

public interface Callback<A> {

    public void call(A val);

}

Main.java

package com.github.kagamilove0707.safelist;

import static com.github.kagamilove0707.safelist.SafeList.*;

public class Main {

    public static void main(String[] args) {
        SafeList<String, ?> list = cons("＞ω＜", SafeList.<String>nil());
        maybe(list, new Callback<SafeList<String, NonEmpty>>() {
            @Override
            public void call(SafeList<String, NonEmpty> list) {
                System.out.println(head(list));
            }
        });
    }
}

SafeList.java

package com.github.kagamilove0707.safelist;

public abstract class SafeList<A, B extends SafeListState> {
    Class<B> type;

    protected SafeList(@SuppressWarnings("unchecked") B ..._type) {
        @SuppressWarnings("unchecked")
        Class<B> type = (Class<B>) _type.getClass().getComponentType();
        this.type = type;
    }

    public static <A> A head(SafeList<A, NonEmpty> list) {
        return list.getHead();
    }

    public static <A> SafeList<A, ?> tail(SafeList<A, NonEmpty> list){
        return list.getTail();
    }

    public static <A> SafeList<A, NonEmpty> cons(final A head, final SafeList<A, ?> tail) {
        return new SafeList<A, NonEmpty>(){
            @Override
            protected A getHead() {
                return head;
            }
            @Override
            protected SafeList<A, ?> getTail() {
                return tail;
            }
        };
    }

    public static <A> SafeList<A, Empty> nil() {
        return new SafeList<A, Empty>(){};
    }

    @SuppressWarnings("unchecked")
    public static <A> void maybe(SafeList<A, ?> list, Callback<SafeList<A, NonEmpty>> callback) {
       if(list.type.equals(NonEmpty.class)) {
           callback.call((SafeList<A, NonEmpty>)list);
       }
    }

    protected A getHead(){
        return null;
    }
    protected SafeList<A, ?> getTail(){
        return null;
    }
}