add uids interface

package cn.edu.sustech.cs307.factory;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

public abstract class ServiceFactory {

    protected <T> void registerService(Class<T> serviceClass, T implementationInstance) {

        services.put(serviceClass, implementationInstance);

    }

    public abstract List<String> getUIDs();

}