3、建造者模式

定义

将一个复杂对象的创建与它的表示分离，使得同样的构建过程可以创建不同的表示
用户只需要建造的类型就可以得到它们，建造过程及细节不需要知道

类型

创建型

适用场景

1、如果一个对象有非常复杂得内部结构（很多属性）
2、想把复杂对象的创建和使用分离

优点

1、封装性好，创建和使用分离
2、扩展性好、建造类之间独立、一定程度上解耦

缺点

1、产生多余的builder对象
2、产品内部发生变化，建造者都要修改，成本太大。

与工厂模式区别

1、建造者更注重方法调用顺序 工厂注重创建产品
2、创建对象的力度不同
建造者可以创建一些复杂的产品
3、关注点
工厂创建出来就好了 建造者不止要创建出来还要知道这个产品是那个部件组成的

代码

1、标准写法

//课程实例
public class Course {
    private String courseName;
    private String coursePPT;
    private String courseVideo;
    private String courseArticle;
    private String courseQA;
	//......Getter Setter  toString
}

//课程抽象建造者
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);

    public abstract Course makeCourse();
}

//课程实体建造者
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;
    }
}

//指挥官用于制作课程
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();
    }
}

//测试
public class Test {
    public static void main(String[] args) {
        CourseBuilder courseBuilder = new CourseActualBuilder();
        Coach coach = new Coach();
        coach.setCourseBuilder(courseBuilder);
        Course course = coach.makeCourse("java入门",
                "javaPPT",
                "javaVideo",
                "javaArticle",
                "javaQA"
                );
        System.out.println(course);
    }
}

UML类图

2、优化写法

public class Course {
    private String courseName;
    private String coursePPT;
    private String courseVideo;
    private String courseArticle;
    private String 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;
    }

    @Override
    public String toString() {
        return "Course{" +
                "courseName='" + courseName + '\'' +
                ", coursePPT='" + coursePPT + '\'' +
                ", courseVideo='" + courseVideo + '\'' +
                ", courseArticle='" + courseArticle + '\'' +
                ", courseQA='" + courseQA + '\'' +
                '}';
    }


    public static class CourseBuilder{
        private String courseName;
        private String coursePPT;
        private String courseVideo;
        private String courseArticle;
        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);
        }
    }
}

//测试
public class Test {
    public static void main(String[] args) {
        Course course = new Course.CourseBuilder().
                buildCourseName("Python课程").
                buildCourseArticle("Py手记").
                buildCoursePPT("PyPPt").
                buildCourseQA("PyQA").buildCourseVideo("Py视频").build();
        System.out.println(course );
    }
}

UML类图

源码应用

1、java.lang.StringBuilder

2、java.lang.Stringbuffer方法加了同步所以线程安全

3、com.google.common.collect.ImmutableSet(guava)