设计模式之建造者模式-蒲公英云

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;
    }
    .....