一.介绍
1.建造者定义:
将一个复杂对象的构建与它的表示分离,使得同样的构建过程可以创建不同的表示 用户只需指定需要建造的类型就可以得到他们,建造过程及细节不需要知道2.类型:
创建型3.适用场景:
如果一个对象有非常复杂的内部结构(很多属性) 想把复杂对象的创建和使用分离4.优点:
封装性好,创建和使用分离 扩展性好,建造者之间独立,一定程度上解耦5.缺点:
产生多余的Builder对象 产品内部发生变化,建造者都要修改,成本较大二.demo演示
1.创建一个课程类和一些基本的属性
public class Course { private String courseName; private String coursePPT; private String courseVideo; private String courseArticle; //问答 private String courseQA; @Override public String toString() { return "Course{" + "courseName='" + courseName + '\'' + ", coursePPT='" + coursePPT + '\'' + ", courseVideo='" + courseVideo + '\'' + ", courseArticle='" + courseArticle + '\'' + ", courseQA='" + courseQA + '\'' + '}'; } public String getCourseName() { return courseName; } public void setCourseName(String courseName) { this.courseName = courseName; } public String getCoursePPT() { return coursePPT; } public void setCoursePPT(String coursePPT) { this.coursePPT = coursePPT; } public String getCourseVideo() { return courseVideo; } public void setCourseVideo(String courseVideo) { this.courseVideo = courseVideo; } public String getCourseArticle() { return courseArticle; } public void setCourseArticle(String courseArticle) { this.courseArticle = courseArticle; } public String getCourseQA() { return courseQA; } public void setCourseQA(String courseQA) { this.courseQA = courseQA; } }2.创建一个CourseBuilder抽象类,并且创建一些接口和制作课程的接口
public abstract class CourseBuilder { public abstract void buildCourseName(String courseName); public abstract void buildCoursePPT(String coursePPT); public abstract void buildCourseVideo(String courseVideo); public abstract void buildCourseArticle(String courseArticle); public abstract void buildCourseQA(String courseQA); //制作课程 public abstract Course makeCourse(); }3.创建CourseActualBuilder真正的实现者
/** * 真正的创造者 */ public class CourseActualBuilder extends CourseBuilder{ private Course course = new Course(); @Override public void buildCourseName(String courseName) { course.setCourseName(courseName); } @Override public void buildCoursePPT(String coursePPT) { course.setCoursePPT(coursePPT); } @Override public void buildCourseVideo(String courseVideo) { course.setCourseVideo(courseVideo); } @Override public void buildCourseArticle(String courseArticle) { course.setCourseArticle(courseArticle); } @Override public void buildCourseQA(String courseQA) { course.setCourseQA(courseQA); } @Override public Course makeCourse() { return course; } }4.创建Coach教练类,相当于指挥官协助讲师进行视频的制作
public class Coach { private CourseBuilder courseBuilder; public void setCourseBuilder(CourseBuilder courseBuilder) { this.courseBuilder = courseBuilder; } public Course makeCourse(String courseName,String coursePPT, String courseVideo,String courseArticle, String courseQA){ this.courseBuilder.buildCourseName(courseName); this.courseBuilder.buildCoursePPT(coursePPT); this.courseBuilder.buildCourseVideo(courseVideo); this.courseBuilder.buildCourseArticle(courseArticle); this.courseBuilder.buildCourseQA(courseQA); return this.courseBuilder.makeCourse(); } }5.测试
public class Coach { private CourseBuilder courseBuilder; public void setCourseBuilder(CourseBuilder courseBuilder) { this.courseBuilder = courseBuilder; } public Course makeCourse(String courseName,String coursePPT, String courseVideo,String courseArticle, String courseQA){ this.courseBuilder.buildCourseName(courseName); this.courseBuilder.buildCoursePPT(coursePPT); this.courseBuilder.buildCourseVideo(courseVideo); this.courseBuilder.buildCourseArticle(courseArticle); this.courseBuilder.buildCourseQA(courseQA); return this.courseBuilder.makeCourse(); } }结果不进行展示了,但是上面的缺点就是属性非常多会导致属性值设置混乱,所以要进行下面的升级
三.demo升级演示
1.创建Course课程类,属性和构造方法,创建CourseBuilder静态内部类,添加课程的属性,创建对应属性赋值的方法,最终返回仍为本类CourseBuilder,创建Course类的构造方法,并且把CourseBuilder以参数的形式传入,然后把静态内部类的中属性的值设置给Course类的成员变量
public class Course { private String courseName; private String coursePPT; private String courseVideo; private String courseArticle; //问答 private String courseQA; @Override public String toString() { return "Course{" + "courseName='" + courseName + '\'' + ", coursePPT='" + coursePPT + '\'' + ", courseVideo='" + courseVideo + '\'' + ", courseArticle='" + courseArticle + '\'' + ", courseQA='" + courseQA + '\'' + '}'; } public Course(CourseBuilder courseBuilder) { this.courseName=courseBuilder.courseName; this.coursePPT=courseBuilder.coursePPT; this.courseVideo=courseBuilder.courseVideo; this.courseArticle=courseBuilder.courseArticle; this.courseQA=courseBuilder.courseQA; } public static class CourseBuilder{ private String courseName; private String coursePPT; private String courseVideo; private String courseArticle; //问答 private String courseQA; public CourseBuilder buildCourseName(String courseName){ this.courseName=courseName; return this; } public CourseBuilder buildCoursePPT(String coursePPT){ this.coursePPT=coursePPT; return this; } public CourseBuilder buildCourseVideo(String courseVideo){ this.courseVideo=courseVideo; return this; } public CourseBuilder buildCourseArticle(String courseArticle){ this.courseArticle=courseArticle; return this; } public CourseBuilder buildCourseQA(String courseQA){ this.courseQA=courseQA; return this; } public Course build(){ return new Course(this); } } }2.测试
public class Test { public static void main(String[] args) { Course course = new Course.CourseBuilder().buildCourseName(“java设计模式”) .buildCourseVideo(“java视频”).buildCoursePPT(“设计模式的PPT”) .buildCourseArticle(“设计模式文章”).build(); System.out.println(course); } }
3.总结: 升级之后的方法好处就是会为对应的属性赋值,不会产生混乱的现象,原理就是,通过内部类的方法赋值给内部类的属性,然后在Course类的构造初始化的时候把内部类属性的值赋值给Course属性的值,最后通过builde方法返回当前已经赋过值的对象.
四.源码中的应用
1.在StringBuilder中的append方法使用的就是标准的建造者模式
@Override public StringBuilder append(String str) { super.append(str); return this; } public StringBuilder append(StringBuffer sb) { super.append(sb); return this; } @Override public StringBuilder append(CharSequence s) { super.append(s); return this; }还有很多append方法,想看的可以自己研究一下
2.Set的实现类ImmutableSet抽象类,看Builder类可以知道是一个标准的建造者模式
public static class Builder<E> extends ImmutableCollection.ArrayBasedBuilder<E> { public Builder() { this(DEFAULT_INITIAL_CAPACITY); } Builder(int capacity) { super(capacity); } @CanIgnoreReturnValue @Override public Builder<E> add(E element) { super.add(element); return this; } .....至此,建造者模式的讲解到此结束.