Java，

Java，

How to write Java?

No.1 static factory method replace constructor

• originally

interface Service{}

ServiceImp implements Service{}

Service service = new ServiceImp(); 

• singleton

public class Server{
    private Service service = null;
    public static Service getService(){
        if(service == null){
            service = new Service();
        }
    }
}

Service service = Server.getService(); 

• static factory method

 // service provider framework
interface Provider{
    Service getInstance();  
}

public class Server{
    private static HashMap<String, Provider> map = new HashMap<String, Provider>();
    private static final DEFAULT_NAME = "Service";

    public void registerDefault(Provdier p){
        map.put(DEFAULT_NAME, p);
    }
    public void register(String name, Provdier p){
        map.put(name, p);
    }

    public static Service getService(){
        return getService(DEFAULT_NAME);
    }

    public static Service getService(name){
        Provider p = map.get(name);
        if(p == null){
            throw new Exception(name);
        }
        return p.getInstance();
    }
}

Server.registerDefault();
Service service = Server.getService();