模式定義

生成器模式將一個複雜物件的構建與它的表示分離，封裝了一個產品的構造過程，並允許按步驟構造。

下圖是該模式的類圖：

一個生動的例子

Product類：
public class Vacation {
	private int day;
	private String hotel;
	private String ticket;
	private String specialEvent;

	public int getDay() {
		return day;
	}

	public void setDay(int day) {
		this.day = day;
 

	}

	public String getHotel() {
		return hotel;
	}

	public void setHotel(String hotel) {
		this.hotel = hotel;
	}

	public String getTicket() {
		return ticket;
	}

	public void setTickets(String ticket) {
		this.ticket = ticket;
	}

	public String getSpecialEvent() {
		return specialEvent;
	}

	public
 
 void setSpecialEvent(String specialEvent) {
		this.specialEvent = specialEvent;
	}

	@Override
	public String toString() {
		return "Vacation [day=" + day + ", hotel=" + hotel + ", ticket=" + ticket + ", specialEvent=" + specialEvent
				+ "]";
	}

}

Builder抽象類：
public abstract class AbstractBuilder
 
 {
	protected Vacation vacation;

	public Vacation getVocationPlanner() {
		return vacation;
	}

	public AbstractBuilder() {
		vacation = new Vacation();
	}

	public abstract void buildDay(int day);

	public abstract void addHotel(String hotel);

	public abstract void addTicket(String ticket);

	public abstract void addSpecialEvent(String specialEvent);

}

Builder實現類：
class VacationBuilder extends AbstractBuilder {

	@Override
	public void buildDay(int day) {
		vacation.setDay(day);
	}

	@Override
	public void addHotel(String hotel) {
		vacation.setHotel(hotel);
	}

	@Override
	public void addTicket(String ticket) {
		vacation.setTickets(ticket);
	}

	@Override
	public void addSpecialEvent(String specialEvent) {
		vacation.setSpecialEvent(specialEvent);
	}
}

客戶端類：
public class BuilderTest {
	public static void main(String[] args) {
		AbstractBuilder vacationBuilder = new VacationBuilder();
		vacationBuilder.buildDay(3);
		vacationBuilder.addHotel("hotel");
		vacationBuilder.addSpecialEvent("specialEvent");
		vacationBuilder.addTicket("ticket");
		Vacation vocationPlanner = vacationBuilder.getVocationPlanner();
		System.out.println(vocationPlanner);
	}
}

參考

1. Head First 設計模式[書籍]
2. 百度百科之建造者模式
3. 簡書之生成器模式