迪米特法則的核心是降低類之間的耦合 , 最少知道原則

import java.util.ArrayList; import java.util.List;public class Demeter1 {public static void main(String[] args){SchoolManager schoolManager = new SchoolManager();schoolManager.printAllEmployee(new CollegeManager());} }// 學?？偛繂T工 class Employee{private String id;public String getId() {return id;}public void setId(String id) {this.id = id;} }//學院總部員工 class CollegeEmployee{private String id;public String getId() {return id;}public void setId(String id) {this.id = id;} }// 管理學院員工的管理類 class CollegeManager{public List<CollegeEmployee> getAllEmployee(){List<CollegeEmployee> list = new ArrayList<CollegeEmployee>();for(int i=0;i<10;i++){CollegeEmployee emp = new CollegeEmployee();emp.setId("學院員工id="+i);list.add(emp);}return list;} }// 分析SchoolManager, 類的直接朋友有哪些 Employee, CollegeManager // CollegeEmployee不是直接朋友,這樣違背了迪米特法則 class SchoolManager{public List<Employee> getAllEmployee(){List<Employee> list = new ArrayList<Employee>();for(int i=0;i<5;i++){Employee emp = new Employee();emp.setId("學?？偛繂T工id="+i);list.add(emp);}return list;}void printAllEmployee(CollegeManager sub){// CollegeEmployee不是直接朋友，應該調整這部分代碼List<CollegeEmployee> list1 = sub.getAllEmployee();System.out.println("------學院員工-----");for(CollegeEmployee e : list1){System.out.println(e.getId());}List<Employee> list2 = this.getAllEmployee();System.out.println("------學校總部員工-----");for(Employee e : list2){System.out.println(e.getId());}} }

改進版

import java.util.ArrayList; import java.util.List;public class Demeter1 {public static void main(String[] args){SchoolManager schoolManager = new SchoolManager();schoolManager.printAllEmployee(new CollegeManager());} }// 學?？偛繂T工 class Employee{private String id;public String getId() {return id;}public void setId(String id) {this.id = id;} }//學院總部員工 class CollegeEmployee{private String id;public String getId() {return id;}public void setId(String id) {this.id = id;} }// 管理學院員工的管理類 class CollegeManager{public List<CollegeEmployee> getAllEmployee(){List<CollegeEmployee> list = new ArrayList<CollegeEmployee>();for(int i=0;i<10;i++){CollegeEmployee emp = new CollegeEmployee();emp.setId("學院員工id="+i);list.add(emp);}return list;}public void printAllEmployee(){// CollegeEmployee不是直接朋友，應該調整這部分代碼List<CollegeEmployee> list1 = getAllEmployee();System.out.println("------學院員工-----");for(CollegeEmployee e : list1){System.out.println(e.getId());}}}// 分析SchoolManager, 類的直接朋友有哪些 Employee, CollegeManager // CollegeEmployee不是直接朋友,這樣違背了迪米特法則 class SchoolManager{public List<Employee> getAllEmployee(){List<Employee> list = new ArrayList<Employee>();for(int i=0;i<5;i++){Employee emp = new Employee();emp.setId("學?？偛繂T工id="+i);list.add(emp);}return list;}void printAllEmployee(CollegeManager sub){sub.printAllEmployee();List<Employee> list2 = this.getAllEmployee();System.out.println("------學?？偛繂T工-----");for(Employee e : list2){System.out.println(e.getId());}} }

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總結

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