静态工厂方法与构造器不同的第一大优势在于，它们有名称。
静态工厂方法与构造器不同的第二大优势在于，不必在每次调用它们的时候都创建一个新对象。
静态工厂方法与构造器不同的第三大优势在于，它们可以返回原返回类型的任何子类型的对象。
静态工厂方法的第四大优势在于，在创建参数化类型实例的时候，它们使代码变得更加简洁。
静态工厂方法的主要缺点在于，类如果不含有公有的或受保护的构造器，就不能被子类化。
静态工厂方法的第二个缺点在于，它们与去他的静态方法实际上没有任何区别。
服务提供者框架：
[
java] // Service provider framework sketch - Service
interface
public interface Service {
// Service-specific methods go here
}
// Service provider framework sketch - Service interface
public interface Service {
// Service-specific methods go here
}
[
java] // Service provider framework sketch - Service provider interface
public interface Provider {
Service newService();
}
// Service provider framework sketch - Service provider interface
public interface Provider {
Service newService();
}[
java] // Service provider framework sketch
// Noninstantiable class for service registration and access
import
java.util.*;
import
java.util.concurrent.*;
public class Services {
private Services() { } // Prevents instantiation (Item 4)
// Maps service names to services
private static final Map<String, Provider> providers =
new ConcurrentHashMap<String, Provider>();
public static final String DEFAULT_PROVIDER_NAME = "<def>";
// Provider registration API
public static void registerDefaultProvider(Provider p) {
registerProvider(DEFAULT_PROVIDER_NAME, p);
}
public static void registerProvider(String name, Provider p){
providers.put(name, p);
}
// Service access API
public static Service newInstance() {
return newInstance(DEFAULT_PROVIDER_NAME);
}
public static Service newInstance(String name) {
Provider p = providers.get(name);
if (p == null)
throw new IllegalArgumentException(
"No provider registered with name: " + name);
return p.newService();
}
}
// Service provider framework sketch
// Noninstantiable class for service registration and access
import
java.util.*;
import
java.util.concurrent.*;
public class Services {
private Services() { } // Prevents instantiation (Item 4)
// Maps service names to services
private static final Map<String, Provider> providers =
new ConcurrentHashMap<String, Provider>();
public static final String DEFAULT_PROVIDER_NAME = "<def>";
// Provider registration API
public static void registerDefaultProvider(Provider p) {
registerProvider(DEFAULT_PROVIDER_NAME, p);
}
public static void registerProvider(String name, Provider p){
providers.put(name, p);
}
// Service access API
public static Service newInstance() {
return newInstance(DEFAULT_PROVIDER_NAME);
}
public static Service newInstance(String name) {
Provider p = providers.get(name);
if (p == null)
throw new IllegalArgumentException(
"No provider registered with name: " + name);
return p.newService();
}
}
[
java] // Simple test program for service provider framework
public class Test {
public static void main(String[] args) {
// Providers would execute these lines
Services.registerDefaultProvider(DEFAULT_PROVIDER);
Services.registerProvider("comp", COMP_PROVIDER);
Services.registerProvider("armed", ARMED_PROVIDER);
// Clients would execute these lines
Service s1 = Services.newInstance();
Service s2 = Services.newInstance("comp");
Service s3 = Services.newInstance("armed");
System.out.printf("%s, %s, %s%n", s1, s2, s3);
}
private static Provider DEFAULT_PROVIDER = new Provider() {
public Service newService() {
return new Service() {
@Override public String toString() {
return "Default service";
}
};
}
};
private static Provider COMP_PROVIDER = new Provider() {
public Service newService() {
return new Service() {
@Override public String toString() {
return "Complementary service";
}
};
}
};
private static Provider ARMED_PROVIDER = new Provider() {
public Service newService() {
return new Service() {
@Override public String toString() {
return "Armed service";
}
};
}
};
}
