定义

定义一个用于创建对象的接口，让子类决定实例化哪个类

使用场景

在任何需要生成复杂对象的地方，都可以使用工厂模式

UML类图

抽象工厂UML图

上面是抽象接口类的结构层次，下面我们用网络套餐举例

Meal.java

public abstract class Meal {

    private User user;
    private String name;
    private float price;

    public abstract void method();

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public float getPrice() {
        return price;
    }

    public void setPrice(float price) {
        this.price = price;
    }
}

CommonMeal.java

public class CommonMeal extends Meal{

    @Override
    public void method() {
        System.out.print("普通套餐");
    }
}

SpeedMeal.java

public class SpeedMeal extends Meal {
    @Override
    public void method() {
        System.out.print("高速套餐");
    }
}

Factory.java

public abstract class Factory <T extends Meal>{

    public abstract T createMeal();
}

CommonFactory.java

public class CommonFactory extends Factory<CommonMeal>{
    @Override
    public CommonMeal createMeal() {
        CommonMeal meal = new CommonMeal();
        meal.setName("xxx");
        meal.setPrice(20f);
        User user = new User();
        user.setSerial("xxx");
        meal.setUser(user);
        return meal;
    }
}

SpeedFactory.java

public class SpeedFactory extends Factory<SpeedMeal> {

    @Override
    public SpeedMeal createMeal() {
        SpeedMeal meal = new SpeedMeal();
        meal.setName("xxx");
        meal.setPrice(30f);
        User user = new User();
        user.setSerial("xxx");
        meal.setUser(user);
        return meal;
    }
}

调用

//生成普通套餐
CommonFactory commonFactory = new CommonFactory();
CommonMeal commonMeal = commonFactory.createMeal();

//生成高速套餐
SpeedFactory speedFactory = new SpeedFactory();
SpeedMeal speedMeal = speedFactory.createMeal();

总结

优点

• 降低了对象之间的耦合度
• 代码结构清晰，对调用者隐藏了产品的生产过程，生产过程改变后，调用者不用做什么改变，易于修改
• 易于拓展，要增加工厂和产品都非常方便，直接实现接口，不用修改之前的代码。

缺点

增加代码结构层次，如果是简单的new就可以得到对象不建议用工厂模式