桥接模式

桥接模式（Bridge Pattern）也叫做桥梁模式，是一个比较简单的模式，其定义如下： Decouple an abstraction from its implementation so that the two can vary independently.（将抽象和实现解耦，使得两者可以独立地变化。）

例如我们需要发送消息给用户，可以选择短信，也可以选择邮件，并且邮件和短信都可以分为加急消息和普通消息，代码如下：

public interface MessageSender {
	void send(String message, String toUser);
}
/**
 * @Description: 邮件发送
 */
class EmailMessageSender implements MessageSender {
	@Override
	public void send(String message, String toUser) {
		// TODO Auto-generated method stub
	}
}
/**
 * @Description: 短信发送
 */
class SmsMessageSender implements MessageSender {
	@Override
	public void send(String message, String toUser) {
		// TODO Auto-generated method stub
	}
}

创建一个桥接抽象角色类

public class AbstractMessageSender {
	
	private MessageSender messageSender;

	public AbstractMessageSender(MessageSender messageSender) {
		this.messageSender = messageSender;
	}

	public void sendMessage(String message, String toUser) {
		this.messageSender.send(message, toUser);
	}
}

创建一个普通消息类

public class NomalMessage extends AbstractMessageSender {

	public NomalMessage(MessageSender messageSender) {
		super(messageSender);
	}

	@Override
	public void sendMessage(String message, String toUser) {
		super.sendMessage(message, toUser);
	}
	
}

创建一个加急消息类

class UrgencyMessage extends AbstractMessageSender {

	public UrgencyMessage(MessageSender messageSender) {
		super(messageSender);
	}

	@Override
	public void sendMessage(String message, String toUser) {
		message = "加急：" + message;
		super.sendMessage(message, toUser);
	}
	
}

使用

	public static void main(String[] args) {
		MessageSender messageSender = new SmsMessageSender();
		AbstractMessageSender abstractMessageSender = new NomalMessage(messageSender);
		abstractMessageSender.sendMessage("普通消息", "张三");
		
		messageSender = new EmailMessageSender();
		abstractMessageSender = new UrgencyMessage(messageSender);
		abstractMessageSender.sendMessage("加急消息", "李四");
	}