代码：

 public static void main(String[] args) {
        Person2 person=new Person2("唐僧",new Horse());
   person.passRiver();
   person.onRoad();
    }

接口：

interface  Vehicles{
    public void work();
}

lass Horse implements Vehicles{

    @Override
    public  void work() {
        System.out.println("大陆骑马去");
    }
}

class Boat implements  Vehicles{

    @Override
    public void work() {
        System.out.println("过河坐船去");
    }
}

class Person2{
    private String name;
    private Vehicles Vehicles;

    public Person2(String name, Vehicles vehicles) {
        this.name = name;
        Vehicles = vehicles;
    }
    public void passRiver() {
        if (Vehicles == null) {
            Vehicles = VehiclesFactory.getBoat();
        }
            //过河，先从工厂获取一艘船
            Boat boat = VehiclesFactory.getBoat();
            boat.work();
        }
        public void onRoad () {
            //判断当前属性是否已经存在
            if (Vehicles == null) {
                Vehicles = VehiclesFactory.getHorse();
            }
            //过河，先从工厂获取一艘船
            Horse horse = VehiclesFactory.getHorse();
            horse.work();
        }

}

public class VehiclesFactory {
    //写static，可以直接调用方法，不用创建对象
    public static Horse getHorse() {
        return new Horse();
    }

    public static Boat getBoat() {
        return new Boat();
    }
}

结果：