涉及模式讲究的是一个平衡和业务模型的匹配。

定义

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
特征：用户只需指定需要构建的类型就可以得到他们，建造过程及细节不需要知道
类型：创建型

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

    优点

  • 封装性好，创建和使用分离

  • 扩展性好、建造类之间独立，一定程度上解耦

    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

    Coding

    Course

    1. public class Course {
    2.   private String courseName;
    3.   private String coursePPT;
    4.   private String courseVideo;
    5.   private String courseArticle;
    7.   //question & answer
    8.   private String courseQA;
    10.   public String getCourseName() {
    11.       return courseName;
    12.   }
    14.   public void setCourseName(String courseName) {
    15.       this.courseName = courseName;
    16.   }
    18.   public String getCoursePPT() {
    19.       return coursePPT;
    20.   }
    22.   public void setCoursePPT(String coursePPT) {
    23.       this.coursePPT = coursePPT;
    24.   }
    26.   public String getCourseVideo() {
    27.       return courseVideo;
    28.   }
    30.   public void setCourseVideo(String courseVideo) {
    31.       this.courseVideo = courseVideo;
    32.   }
    34.   public String getCourseArticle() {
    35.       return courseArticle;
    36.   }
    38.   public void setCourseArticle(String courseArticle) {
    39.       this.courseArticle = courseArticle;
    40.   }
    42.   public String getCourseQA() {
    43.       return courseQA;
    44.   }
    46.   public void setCourseQA(String courseQA) {
    47.       this.courseQA = courseQA;
    48.   }
    50.   @Override
    51.   public String toString() {
    52.       return "Course{" +
    53.               "courseName='" + courseName + '\'' +
    54.               ", coursePPT='" + coursePPT + '\'' +
    55.               ", courseVideo='" + courseVideo + '\'' +
    56.               ", courseArticle='" + courseArticle + '\'' +
    57.               ", courseQA='" + courseQA + '\'' +
    58.               '}';
    59.   }
    60. }

    CourseBuilder

    1. public abstract class CourseBuilder {
    2.   public abstract void buildCourseName(String courseName);
    3.   public abstract void buildCoursePPT(String coursePPT);
    4.   public abstract void buildCourseVideo(String courseVideo);
    5.   public abstract void buildCourseArticle(String courseArticle);
    6.   public abstract void buildCourseQA(String courseQA);
    7.   public abstract Course makeCourse();
    8. }

    CourseActualBuilder ```java public class CourseActualBuilder extends CourseBuilder {

    private Course course = new Course();

  1. @Override
  2. public void buildCourseName(String courseName) {
  3.     course.setCourseName(courseName);
  4. }
  6. @Override
  7. public void buildCoursePPT(String coursePPT) {
  8.     course.setCoursePPT(coursePPT);
  9. }
  11. @Override
  12. public void buildCourseVideo(String courseVideo) {
  13.     course.setCourseVideo(courseVideo);
  14. }
  16. @Override
  17. public void buildCourseArticle(String courseArticle) {
  18.     course.setCourseArticle(courseArticle);
  19. }
  21. @Override
  22. public void buildCourseQA(String courseQA) {
  23.     course.setCourseQA(courseQA);
  24. }
  26. @Override
  27. public Course makeCourse() {
  28.     return course;
  29. }

}

  1. Coach
  2. ```java
  3. public class Coach {
  4.     private CourseBuilder courseBuilder;
  6.     public void setCourseBuilder(CourseBuilder courseBuilder) {
  7.         this.courseBuilder = courseBuilder;
  8.     }
  10.     public Course makeCourse(String courseName,String coursePPT,
  11.                              String courseVideo,String courseArticle,
  12.                              String courseQA){
  13.         this.courseBuilder.buildCourseName(courseName);
  14.         this.courseBuilder.buildCoursePPT(coursePPT);
  15.         this.courseBuilder.buildCourseVideo(courseVideo);
  16.         this.courseBuilder.buildCourseArticle(courseArticle);
  17.         this.courseBuilder.buildCourseQA(courseQA);
  18.         return this.courseBuilder.makeCourse();
  19.     }
  20. }

Test

  1. public class Test {
  2.     public static void main(String[] args) {
  3.         CourseBuilder courseBuilder = new CourseActualBuilder();
  4.         Coach coach = new Coach();
  5.         coach.setCourseBuilder(courseBuilder);
  6.         Course course = coach.makeCourse("Java设计模式精讲",
  7.                 "Java设计模式精讲PPT",
  8.                 "Java设计模式精讲视频",
  9.                 "Java设计模式精讲手记",
  10.                 "Java设计模式精讲问答");
  11.         System.out.println(course);
  12.     }
  13. }

V2

  1. public class Course {
  3.     private String courseName;
  4.     private String coursePPT;
  5.     private String courseVideo;
  6.     private String courseArticle;
  8.     //question & answer
  9.     private String courseQA;
  11.     public Course(CourseBuilder courseBuilder) {
  12.         this.courseName = courseBuilder.courseName;
  13.         this.coursePPT = courseBuilder.coursePPT;
  14.         this.courseVideo = courseBuilder.courseVideo;
  15.         this.courseArticle = courseBuilder.courseArticle;
  16.         this.courseQA = courseBuilder.courseQA;
  17.     }
  20.     @Override
  21.     public String toString() {
  22.         return "Course{" +
  23.                 "courseName='" + courseName + '\'' +
  24.                 ", coursePPT='" + coursePPT + '\'' +
  25.                 ", courseVideo='" + courseVideo + '\'' +
  26.                 ", courseArticle='" + courseArticle + '\'' +
  27.                 ", courseQA='" + courseQA + '\'' +
  28.                 '}';
  29.     }
  31.     public static class CourseBuilder{
  32.         private String courseName;
  33.         private String coursePPT;
  34.         private String courseVideo;
  35.         private String courseArticle;
  37.         //question & answer
  38.         private String courseQA;
  40.         public CourseBuilder buildCourseName(String courseName){
  41.             this.courseName = courseName;
  42.             return this;
  43.         }
  46.         public CourseBuilder buildCoursePPT(String coursePPT) {
  47.             this.coursePPT = coursePPT;
  48.             return this;
  49.         }
  51.         public CourseBuilder buildCourseVideo(String courseVideo) {
  52.             this.courseVideo = courseVideo;
  53.             return this;
  54.         }
  56.         public CourseBuilder buildCourseArticle(String courseArticle) {
  57.             this.courseArticle = courseArticle;
  58.             return this;
  59.         }
  61.         public CourseBuilder buildCourseQA(String courseQA) {
  62.             this.courseQA = courseQA;
  63.             return this;
  64.         }
  66.         public Course build(){
  67.             return new Course(this);
  68.         }
  70.     }
  71. }

Test

  1. public class Test {
  2.     public static void main(String[] args) {
  3.         // 链式调用
  4.         Course course = new Course.CourseBuilder().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").build();
  5.         System.out.println(course);
  6.     }
  7. }

典型用例

StringBuilder
StringBuffer