建造者模式

一种场景：客户需要设计一个汽车模型，基本的功能有启动、停止、按喇叭、引擎这些功能，
执行的顺序由客户自己控制。
时间紧迫的情况下，我们设计出这种模型：

public abstract class CarModel {

	private ArrayList sequence = new ArrayList<>();

	protected abstract void  start();

	protected abstract void stop();

	protected abstract void alarm();

	protected abstract void engineBoom();

	 final public void run()
	{
		for(int i =0; i< this.sequence.size() ;i++)
		{
			String actionName = this.sequence.get(i);
			if(actionName.equalsIgnoreCase("start"))
			{
				this.start();
			}
			else if(actionName.equalsIgnoreCase("stop"))
			{
				this.stop();
			}
			else if(actionName.equalsIgnoreCase("alarm"))
			{
				this.alarm();
			}
			else if(actionName.equalsIgnoreCase("engine"))
			{
				this.engineBoom();
			}

		}

	}

	public ArrayList getSequence() {
		return sequence;
	}

	public void setSequence(ArrayList sequence) {
		this.sequence = sequence;
	}

	//setSequence允许客户设置一个顺序，是先响喇叭还是先启动。对于一个具体的模型
	//永远是固定的，但是对于支持N个模型就是动态的了	
}


public class BenzModel extends CarModel{

	@Override
	protected void start() {
		System.out.println("BenzModel.start()");
	}

	@Override
	protected void stop() {
		System.out.println("BenzModel.stop()");
	}

	@Override
	protected void alarm() {
		System.out.println("BenzModel.alarm()");
	}

	@Override
	protected void engineBoom() {
		System.out.println("BenzModel.engineBoom()");
	}


}


public class BmwModel extends CarModel{

	@Override
	protected void start() {
		System.out.println("BmwModel.start()");
	}

	@Override
	protected void stop() {
		System.out.println("BmwModel.stop()");
	}

	@Override
	protected void alarm() {
		System.out.println("BmwModel.alarm()");
	}

	@Override
	protected void engineBoom() {
		System.out.println("BmwModel.engineBoom()");
	}


}


public class Client {

	public static void main(String[] args) {

		BenzModel benzModel = new  BenzModel();
		ArrayList sequence =  new ArrayList<>();

		sequence.add("engine");
		sequence.add("start");
		sequence.add("stop");

		benzModel.setSequence(sequence);
		benzModel.run(); 
	}	
}

执行结果如下：
BenzModel.engineBoom()
BenzModel.start()
BenzModel.stop()


显然，这样能满足客户的需求，但是如果客户需要N多种模型，势必要在每一处执行
模型的创建和sequence的指定。

试想，有没有改进方法，我们可以尝试将CarModel的创建封装起来，我们增加一个CarBuidler抽象类。具体的类图如下:

[img]http://dl2.iteye.com/upload/attachment/0124/8355/f8680167-84c6-3296-b17e-a4cdd1c4e8a2.png[/img]
代码如下：

public  abstract class CarBuilder {

	public abstract void setSequence(ArrayList sequence);

	public abstract CarModel getCarModel();
}


public class BenzBuilder extends CarBuilder{

	private BenzModel benzModel = new BenzModel();
	@Override
	public void setSequence(ArrayList sequence) {		
		this.benzModel.setSequence(sequence);
	}

	@Override
	public CarModel getCarModel() {
		// TODO Auto-generated method stub
		return this.benzModel;
	}

}


public class BmwBuilder extends CarBuilder{

	private BmwModel bmw = new BmwModel();

	@Override
	public void setSequence(ArrayList sequence) {
		this.bmw.setSequence(sequence);
	}

	@Override
	public CarModel getCarModel() {
		return this.bmw;
	}
}

测试代码如下：
BenzModel benzModel = new  BenzModel();
		ArrayList sequence =  new ArrayList<>();

		sequence.add("engine");
		sequence.add("start");
		sequence.add("stop");

		BenzBuilder  benzBuilder = new BenzBuilder();
	    benzBuilder.setSequence(sequence);
	    CarModel benz = benzBuilder.getCarModel();
	    benz.run();

	    //假设bmw也有这种顺序
	    BmwBuilder  bmwBuilder = new BmwBuilder();
	    bmwBuilder.setSequence(sequence);
	    CarModel bmw = bmwBuilder.getCarModel();
	    bmw.run();

看下上述代码，虽然把对象的创建进行了封装，但还是要在每一处都显示指定sequence，
试想能否进行继续封装，把指定sequence这段过程进行封装。
我们加入Director，相当于一个上下文概念，里面包含了 各种Builder来构建
多种模型功能。相关的类图如下：
[img]http://dl2.iteye.com/upload/attachment/0124/8357/c364c35f-c16c-3476-93e6-d6f0acdfcf30.png[/img]


相关的代码变更如下:

public class Director {

	private ArrayList sequence = new ArrayList<>();

	private BenzBuilder benzBuilder = new BenzBuilder();

	private BmwBuilder bmwBuilder = new BmwBuilder();

	public BenzModel getABenzModel()
	{
		this.sequence.clear();
		this.sequence.add("start");
		this.sequence.add("stop");
		this.benzBuilder.setSequence(sequence);
		return (BenzModel)this.benzBuilder.getCarModel();
	}



	public BenzModel getBBenzModel()
	{
		this.sequence.clear();
		this.sequence.add("engine");
		this.sequence.add("start");
		this.sequence.add("stop");
		this.benzBuilder.setSequence(sequence);
		return (BenzModel)this.benzBuilder.getCarModel();

	}



	public BmwModel getCBMWModel()
	{
		this.sequence.clear();
		this.sequence.add("alarm");
		this.sequence.add("start");
		this.sequence.add("stop");
		this.bmwBuilder.setSequence(sequence);
		return (BmwModel)this.bmwBuilder.getCarModel();
	}

	public BmwModel getDBMWModel()
	{
		this.sequence.clear();
		this.sequence.add("alarm");
		this.bmwBuilder.setSequence(sequence);
		return (BmwModel)this.bmwBuilder.getCarModel();
	}



}


public class Client {

	public static void main(String[] args) {
	    Director director = new Director();
	    for(int i =0; i<10;i++)
	    {
	    	director.getABenzModel().run();
	    }

	    for(int i =0; i<100;i++)
	    {
	    	director.getBBenzModel().run();
	    }


	    for(int i =0; i<1000;i++)
	    {
	    	director.getCBMWModel().run();
	    }



	}



}

建造者模式的执行场景:
相同的方法不同的执行顺序产生不同的执行结构。
多个零配件可以装配到一个对象中，但是产生的运行结果又不同时可以使用该模式。
和工厂模式的区别是，工厂模式注重生产产品的过程，构建者模式重在构建过程的顺序不同