设计模式第4篇：抽象工厂模式

本文翻译自：https://www.journaldev.com/1418/abstract-factory-design-pattern-in-java

Abstract Factory

如果你熟悉工厂方法模式（工厂模式），你会注意到我们只有一个工厂类，这个工厂类返回一个对象是基于你的输入，然后做if-else判断得到的。然而在抽象工厂模式中，我们将摆脱这种方式，会基于输入的工厂类型来做相应的输出；看起来是更加复杂了，但是一旦掌握了，你会觉得它很简单；so easy!

Abstract Factory Design Pattern Super Class and Subclasses

Computer.java

package com.journaldev.design.model;
 
public abstract class Computer {
     
    public abstract String getRAM();
    public abstract String getHDD();
    public abstract String getCPU();
     
    @Override
    public String toString(){
        return "RAM= "+this.getRAM()+", HDD="+this.getHDD()+", CPU="+this.getCPU();
    }
}

PC.java

package com.journaldev.design.model;
 
public class PC extends Computer {
 
    private String ram;
    private String hdd;
    private String cpu;
     
    public PC(String ram, String hdd, String cpu){
        this.ram=ram;
        this.hdd=hdd;
        this.cpu=cpu;
    }
    @Override
    public String getRAM() {
        return this.ram;
    }
 
    @Override
    public String getHDD() {
        return this.hdd;
    }
 
    @Override
    public String getCPU() {
        return this.cpu;
    }
 
}

Server.java

package com.journaldev.design.model;
 
 
public class Server extends Computer {
 
    private String ram;
    private String hdd;
    private String cpu;
     
    public Server(String ram, String hdd, String cpu){
        this.ram=ram;
        this.hdd=hdd;
        this.cpu=cpu;
    }
    @Override
    public String getRAM() {
        return this.ram;
    }
 
    @Override
    public String getHDD() {
        return this.hdd;
    }
 
    @Override
    public String getCPU() {
        return this.cpu;
    }
 
}

Factory Class for Each subclass(针对每一个子类的工厂类)

ComputerAbstractFactory.java

package com.journaldev.design.abstractfactory;

import com.journaldev.design.model.Computer;

public interface ComputerAbstractFactory {

    public Computer createComputer();

}

注意createComputer() 方法的返回类型是Computer，之后的工厂类将会实现这个接口；

PCFactory.java

package com.journaldev.design.abstractfactory;

import com.journaldev.design.model.Computer;
import com.journaldev.design.model.PC;

public class PCFactory implements ComputerAbstractFactory {

    private String ram;
    private String hdd;
    private String cpu;
    
    public PCFactory(String ram, String hdd, String cpu){
        this.ram=ram;
        this.hdd=hdd;
        this.cpu=cpu;
    }
    @Override
    public Computer createComputer() {
        return new PC(ram,hdd,cpu);
    }

}

ServerFactory.java

package com.journaldev.design.abstractfactory;

import com.journaldev.design.model.Computer;
import com.journaldev.design.model.Server;

public class ServerFactory implements ComputerAbstractFactory {

    private String ram;
    private String hdd;
    private String cpu;
    
    public ServerFactory(String ram, String hdd, String cpu){
        this.ram=ram;
        this.hdd=hdd;
        this.cpu=cpu;
    }
    
    @Override
    public Computer createComputer() {
        return new Server(ram,hdd,cpu);
    }

}

ComputerFactory.java

package com.journaldev.design.abstractfactory;

import com.journaldev.design.model.Computer;

public class ComputerFactory {

    public static Computer getComputer(ComputerAbstractFactory factory){
        return factory.createComputer();
    }
}

注意到这个是简单的类，getComputer方法的参数是ComputerAbstractFactory，至此整个实现需要简洁明了；接下来请看一个小测试：

TestDesignPatterns.java

package com.journaldev.design.test;

import com.journaldev.design.abstractfactory.PCFactory;
import com.journaldev.design.abstractfactory.ServerFactory;
import com.journaldev.design.factory.ComputerFactory;
import com.journaldev.design.model.Computer;

public class TestDesignPatterns {

    public static void main(String[] args) {
        testAbstractFactory();
    }

    private static void testAbstractFactory() {
        Computer pc = ComputerFactory.getComputer(new PCFactory("2 GB","500 GB","2.4 GHz"));
        Computer server = ComputerFactory.getComputer(new ServerFactory("16 GB","1 TB","2.9 GHz"));
        System.out.println("AbstractFactory PC Config::"+pc);
        System.out.println("AbstractFactory Server Config::"+server);
    }
}

输出结果：

AbstractFactory PC Config::RAM= 2 GB, HDD=500 GB, CPU=2.4 GHz
AbstractFactory Server Config::RAM= 16 GB, HDD=1 TB, CPU=2.9 GHz

Abstract Factory Design Pattern Examples in JDK（抽象工厂模式在JDK中的运用）

• javax.xml.parsers.DocumentBuilderFactory#newInstance()
• javax.xml.transform.TransformerFactory#newInstance()
• javax.xml.xpath.XPathFactory#newInstance()