工厂模式

Map hashMap=new HashMap();
Map treeMap=new TreeMap();
如果接口的类越来越多？

public class Factory {
    public static Map creator(int which) {
        if (which == 1) {
            return new HashMap();
        } else if (which == 2) {
            new TreeMap();
        }
        return null;
    }
}
Map hashMap = Factory.creator(1);
优点：我们无需提供具体的子类类名，只需要提供一个字符串即可得到相应的实例对象。这样的话，当子类的类名更换或者增加子类时我们都无需修改客户端代码，只需要在简单工厂类上增加一个分支判断代码即可。
缺点：所有内容全部放在工厂里面了，导致工厂类比较复杂

工厂接口
public interface FactoryInterface {
    Map creator();
}
工厂实现类
public class HashMapFactory implements FactoryInterface {
    public Map creator() {
        System.out.println("hashmap");
        return new HashMap();
    }
}
public class TreeMapFactory implements FactoryInterface {
    public Map creator() {
        System.out.println("treeMap");
        return new TreeMap();
    }
}

FactoryInterface hashMapFactory = (FactoryInterface) Class.forName("com.jd.xq.HashMapFactory").newInstance();
FactoryInterface treeMapFactory = (FactoryInterface) Class.forName("com.jd.xq.TreeMapFactory").newInstance();
Map treeMap = treeMapFactory.creator();
Map hashMap = hashMapFactory.creator();