60 lines
2.1 KiB
Markdown
60 lines
2.1 KiB
Markdown
## 工厂方法（Factory Method）
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### Intent
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定义了一个创建对象的接口，但由子类决定要实例化哪个类。工厂方法把实例化操作推迟到子类。
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### Class Diagram
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在简单工厂中，创建对象的是另一个类，而在工厂方法中，是由子类来创建对象。
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下图中，Factory 有一个 doSomething() 方法，这个方法需要用到一个产品对象，这个产品对象由 factoryMethod() 方法创建。该方法是抽象的，需要由子类去实现。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/f4d0afd0-8e78-4914-9e60-4366eaf065b5.png"/> </div><br>
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### Implementation
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```java
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public abstract class Factory {
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abstract public Product factoryMethod();
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public void doSomething() {
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Product product = factoryMethod();
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// do something with the product
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}
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}
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```
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```java
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public class ConcreteFactory extends Factory {
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public Product factoryMethod() {
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return new ConcreteProduct();
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}
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}
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```
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```java
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public class ConcreteFactory1 extends Factory {
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public Product factoryMethod() {
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return new ConcreteProduct1();
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}
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}
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```
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```java
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public class ConcreteFactory2 extends Factory {
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public Product factoryMethod() {
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return new ConcreteProduct2();
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}
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}
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```
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### JDK
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- [java.util.Calendar](http://docs.oracle.com/javase/8/docs/api/java/util/Calendar.html#getInstance--)
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- [java.util.ResourceBundle](http://docs.oracle.com/javase/8/docs/api/java/util/ResourceBundle.html#getBundle-java.lang.String-)
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- [java.text.NumberFormat](http://docs.oracle.com/javase/8/docs/api/java/text/NumberFormat.html#getInstance--)
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- [java.nio.charset.Charset](http://docs.oracle.com/javase/8/docs/api/java/nio/charset/Charset.html#forName-java.lang.String-)
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- [java.net.URLStreamHandlerFactory](http://docs.oracle.com/javase/8/docs/api/java/net/URLStreamHandlerFactory.html#createURLStreamHandler-java.lang.String-)
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- [java.util.EnumSet](https://docs.oracle.com/javase/8/docs/api/java/util/EnumSet.html#of-E-)
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- [javax.xml.bind.JAXBContext](https://docs.oracle.com/javase/8/docs/api/javax/xml/bind/JAXBContext.html#createMarshaller--)
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