java 静态工厂

public abstract class Foo {

//继承了Foo的类的集合

private static Map implementations = null;

    private static synchronized void initMapIfNecessary() {

if (null == implementations) {

implementations = new HashMap();

}

    }

    

            public static Foo getInstance(String key) {

initMaoIfNecessary();

Class c = (Class) implementations.get(key);

if(c == null)

return new DefaultFoo();

try {

return (Foo) c.newInstance();

} catch(Exception e) {

return new DefaultFoo();

}

    }

}