Course.java

public class Course {

    private String courseName;
    private String coursePPT;
    private String courseVideo;
    private String courseArticle;

    //question & answer
    private String courseQA;

    public Course buildCourseName(String courseName){
        this.courseName = courseName;
        return this;
    }

    public Course buildCoursePPT(String coursePPT) {
        this.coursePPT = coursePPT;
        return this;
    }

    public Course buildCourseVideo(String courseVideo) {
        this.courseVideo = courseVideo;
        return this;
    }

    public Course buildCourseArticle(String courseArticle) {
        this.courseArticle = courseArticle;
        return this;
    }

    public Course buildCourseQA(String courseQA) {
        this.courseQA = courseQA;
        return this;
    }

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

Test.java

public class Test {
    public static void main(String[] args) {
        Course course = new Course();
        course.buildCourseName("Java设计模式精讲").buildCoursePPT("Java设计模式精讲PPT").buildCourseVideo("Java设计模式精讲视频");
        System.out.println(course);

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

        System.out.println(set);
    }
}

这样去掉static的内部类，和V2版本有内部static类有什么区别，或者说为什么定义个static内部类是出于哪方面的考虑