设计模式原则
设计模式示例代码库地址：
https://gitee.com/Jasonpupil/designPatterns
迪米特法则原则：
- 意义在于降低类之间的耦合。由于每个对象尽量减少对于其他对象的了解，因此，很容易使得系统的功能模块功能独立，相互之间不存在（或很少有）依赖关系
- 迪米特法则还有一个英文解释是：talk only to your immediate friends（只和直接的朋友交流）
- 什么是朋友：每个对象基本上会与其他的对象有耦合关系，当两个对象之间耦合就会成为朋友关系
- 什么是直接朋友：出现在成员变量、局部变量、全局变量和方法的输入输出参数中的类就是直接的朋友
模式场景：学生成绩&排名
- 迪米特法则替换前：教师管理班级里的学生，校长通过教师获取班里的学生来统计出班级的总分、平均分和班级人数
- 迪米特法则替换后：教师管理班级里的学生，统计出班级的总分、平均分和班级人数由教师来做，校长只需要根据班级寻找老师获取相应的信息
迪米特法则替换前示例代码：
校长类：
/*** @Description: 校长* @Author: pupil* @Date: 2024/06/24 下午 1:13*/
public class Principal {private Teacher teacher = new Teacher("智盛", "3年1班");// 查询班级信息，总分数、学生人数、平均值public Map<String, Object> queryClazzInfo(String clazzId) {// 获取班级信息；学生总人数、总分、平均分int stuCount = clazzStudentCount();double totalScore = clazzTotalScore();double averageScore = clazzAverageScore();// 组装对象，实际业务开发会有对应的类Map<String, Object> mapObj = new HashMap<>();mapObj.put("班级", teacher.getClazz());mapObj.put("老师", teacher.getName());mapObj.put("学生人数", stuCount);mapObj.put("班级总分数", totalScore);mapObj.put("班级平均分", averageScore);return mapObj;}// 总分public double clazzTotalScore() {double totalScore = 0;for (Student stu : teacher.getStudents()) {totalScore += stu.getScore();}return totalScore;}// 平均分public double clazzAverageScore(){double totalScore = 0;for (Student stu : teacher.getStudents()) {totalScore += stu.getScore();}return totalScore / teacher.getStudents().size();}// 班级人数public int clazzStudentCount(){return teacher.getStudents().size();}}老师类：
/*** @Description: 教师* @Author: pupil* @Date: 2024/06/24 下午 1:14*/
public class Teacher {private String name; // 学生姓名private String clazz; // 班级private static List<Student> students; // 学生public Teacher() {}public Teacher(String name, String clazz) {this.name = name;this.clazz = clazz;}static {students = new ArrayList<>();students.add(new Student("王五", 10, 589));students.add(new Student("李四", 100, 256));students.add(new Student("小三", 23, 449));students.add(new Student("皮皮", 2, 665));students.add(new Student("蛋蛋", 15, 532));}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getClazz() {return clazz;}public void setClazz(String clazz) {this.clazz = clazz;}public static List<Student> getStudents() {return students;}public static void setStudents(List<Student> students) {Teacher.students = students;}
}
学生类：
/*** @Description: 学生* @Author: pupil* @Date: 2024/06/24 下午 1:14*/
public class Student {private String name; // 学生姓名private int rank; // 考试排名（总排名）private double score; // 考试分数（总分）public Student() {}public Student(String name, int rank, double score) {this.name = name;this.rank = rank;this.score = score;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getRank() {return rank;}public void setRank(int rank) {this.rank = rank;}public double getScore() {return score;}public void setScore(double score) {this.score = score;}
}
测试类：
/*** @Description: 测试验证* @Author: pupil* @Date: 2024/06/24 下午 3:09*/
public class ApiTest {private Logger logger = LoggerFactory.getLogger(ApiTest.class);@Testpublic void test_Principal(){Principal principal = new Principal();Map<String, Object> map = principal.queryClazzInfo("3年1班");logger.info("查询结果：{}", JSON.toJSONString(map));}
}
结果：
迪米特法则替换后示例代码：
校长类：
/*** @Description: 校长* @Author: pupil* @Date: 2024/06/24 下午 1:13*/
public class Principal {private Teacher teacher = new Teacher("智盛", "3年1班");// 查询班级信息，总分数、学生人数、平均值public Map<String, Object> queryClazzInfo(String clazzId) {// 获取班级信息；学生总人数、总分、平均分int stuCount = teacher.clazzStudentCount();double totalScore = teacher.clazzTotalScore();double averageScore = teacher.clazzAverageScore();// 组装对象，实际业务开发会有对应的类Map<String, Object> mapObj = new HashMap<>();mapObj.put("班级", teacher.getClazz());mapObj.put("老师", teacher.getName());mapObj.put("学生人数", stuCount);mapObj.put("班级总分数", totalScore);mapObj.put("班级平均分", averageScore);return mapObj;}
}
老师类：
/*** @Description: 教师* @Author: pupil* @Date: 2024/06/24 下午 1:14*/
public class Teacher {private String name; // 学生姓名private String clazz; // 班级private static List<Student> students; // 学生public Teacher() {}public Teacher(String name, String clazz) {this.name = name;this.clazz = clazz;}static {students = new ArrayList<>();students.add(new Student("王五", 10, 589));students.add(new Student("李四", 100, 256));students.add(new Student("小三", 23, 449));students.add(new Student("皮皮", 2, 665));students.add(new Student("蛋蛋", 15, 532));}// 总分public double clazzTotalScore() {double totalScore = 0;for (Student stu : getStudents()) {totalScore += stu.getScore();}return totalScore;}// 平均分public double clazzAverageScore(){double totalScore = 0;for (Student stu : getStudents()) {totalScore += stu.getScore();}return totalScore / getStudents().size();}// 班级人数public int clazzStudentCount(){return getStudents().size();}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getClazz() {return clazz;}public void setClazz(String clazz) {this.clazz = clazz;}public static List<Student> getStudents() {return students;}public static void setStudents(List<Student> students) {Teacher.students = students;}
}
学生类：
/*** @Description: 学生* @Author: pupil* @Date: 2024/06/24 下午 1:14*/
public class Student {private String name; // 学生姓名private int rank; // 考试排名（总排名）private double score; // 考试分数（总分）public Student() {}public Student(String name, int rank, double score) {this.name = name;this.rank = rank;this.score = score;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getRank() {return rank;}public void setRank(int rank) {this.rank = rank;}public double getScore() {return score;}public void setScore(double score) {this.score = score;}
}
测试类：
/*** @Description: 测试验证* @Author: pupil* @Date: 2024/06/24 下午 3:09*/
public class ApiTest {private Logger logger = LoggerFactory.getLogger(ApiTest.class);@Testpublic void test_Principal(){Principal principal = new Principal();Map<String, Object> map = principal.queryClazzInfo("3年1班");logger.info("查询结果：{}", JSON.toJSONString(map));}
}
结果：
根据迪米特法则原则的示例类图：
校长类与教师类是聚合关系
教师类与学生类是聚合关系