TypeScript 工厂方法模式讲解和代码示例

工厂方法是一种创建型设计模式，解决了在不指定具体类的情况下创建产品对象的问题。

工厂方法定义了一个方法，且必须使用该方法代替通过直接调用构造函数来创建对象（ new操作符）的方式。子类可重写该方法来更改将被创建的对象所属类。

如果你不清楚工厂、 工厂方法和抽象工厂模式之间的区别，请参阅工厂模式比较。

进一步了解工厂方法模式

复杂度：

流行度：

使用示例： 工厂方法模式在 TypeScript 代码中得到了广泛使用。当你需要在代码中提供高层次的灵活性时，该模式会非常实用。

识别方法： 工厂方法可通过构建方法来识别，它会创建具体类的对象，但以抽象类型或接口的形式返回这些对象。

概念示例

本例说明了工厂方法设计模式的结构并重点回答了下面的问题：

它由哪些类组成？
这些类扮演了哪些角色？
模式中的各个元素会以何种方式相互关联？

index.ts: 概念示例

/**
 * The Creator class declares the factory method that is supposed to return an
 * object of a Product class. The Creator's subclasses usually provide the
 * implementation of this method.
 */
abstract class Creator {
    /**
     * Note that the Creator may also provide some default implementation of the
     * factory method.
     */
    public abstract factoryMethod(): Product;

    /**
     * Also note that, despite its name, the Creator's primary responsibility is
     * not creating products. Usually, it contains some core business logic that
     * relies on Product objects, returned by the factory method. Subclasses can
     * indirectly change that business logic by overriding the factory method
     * and returning a different type of product from it.
     */
    public someOperation(): string {
        // Call the factory method to create a Product object.
        const product = this.factoryMethod();
        // Now, use the product.
        return `Creator: The same creator's code has just worked with ${product.operation()}`;
    }
}

/**
 * Concrete Creators override the factory method in order to change the
 * resulting product's type.
 */
class ConcreteCreator1 extends Creator {
    /**
     * Note that the signature of the method still uses the abstract product
     * type, even though the concrete product is actually returned from the
     * method. This way the Creator can stay independent of concrete product
     * classes.
     */
    public factoryMethod(): Product {
        return new ConcreteProduct1();
    }
}

class ConcreteCreator2 extends Creator {
    public factoryMethod(): Product {
        return new ConcreteProduct2();
    }
}

/**
 * The Product interface declares the operations that all concrete products must
 * implement.
 */
interface Product {
    operation(): string;
}

/**
 * Concrete Products provide various implementations of the Product interface.
 */
class ConcreteProduct1 implements Product {
    public operation(): string {
        return '{Result of the ConcreteProduct1}';
    }
}

class ConcreteProduct2 implements Product {
    public operation(): string {
        return '{Result of the ConcreteProduct2}';
    }
}

/**
 * The client code works with an instance of a concrete creator, albeit through
 * its base interface. As long as the client keeps working with the creator via
 * the base interface, you can pass it any creator's subclass.
 */
function clientCode(creator: Creator) {
    // ...
    console.log('Client: I\'m not aware of the creator\'s class, but it still works.');
    console.log(creator.someOperation());
    // ...
}

/**
 * The Application picks a creator's type depending on the configuration or
 * environment.
 */
console.log('App: Launched with the ConcreteCreator1.');
clientCode(new ConcreteCreator1());
console.log('');

console.log('App: Launched with the ConcreteCreator2.');
clientCode(new ConcreteCreator2());

Output.txt: 执行结果

App: Launched with the ConcreteCreator1.
Client: I'm not aware of the creator's class, but it still works.
Creator: The same creator's code has just worked with {Result of the ConcreteProduct1}

App: Launched with the ConcreteCreator2.
Client: I'm not aware of the creator's class, but it still works.
Creator: The same creator's code has just worked with {Result of the ConcreteProduct2}

TypeScript 工厂方法模式讲解和代码示例

概念示例

index.ts: 概念示例

Output.txt: 执行结果

工厂方法在其他编程语言中的实现