五、設計模式之建造者

一、建造者定義

將一個複雜對象的構建與它的表示分離,使得一樣的構建過程能夠建立不一樣的表示。
用戶只須要指定須要建立的類型就能夠獲得它們,建造過程及細節不須要知道。

適用場景:
1) 若是一個對象具備很是複雜的內部結構(不少屬性)
2) 想把複雜對象的建立和使用分離

優勢:
1) 封裝性好,建立和使用分離
2) 擴展性好、建造類之間獨立,必定程度上解耦

缺點:
1) 產生多餘的Builder對象
2) 產品內部發生變化,建造者都要修改,成本較大

二、代碼演示

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;
    }

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);
        }
    }
}

public class Test {
    public static void main(String[] args) {
        Course course = new Course.CourseBuilder()
                                  .buildCourseName("Java設計模式精講")
                                  .buildCoursePPT("Java設計模式精講PPT")
                                  .buildCourseVideo("Java設計模式精講視頻").build();
        System.out.println(course);

        Set<String> set = ImmutableSet.<String>builder().add("a").add("b").build();
        System.out.println(set);
    }
}