3-8作业中部门员工统计问题

老师好：

这是我的关联代码，由于要统计人事与市场部的员工人数，我用了两个整型变量进行统计：

//完成员工与部门的双向关联
	public void addEmployee(Employee emp) {
		for(int i=0;i<this.getMyEmployee().length;i++) {
			if(this.getMyEmployee()[i]==null) {
				emp.setEmployeeDep(this);//为参数emp对象设置部门
				this.getMyEmployee()[i]=emp;//部门有哪些员工
				if(this.getMyEmployee()[i].getEmployeeDep().getDepartmentNam().equals("人事部"))
				this.myEmployeeNum+=1;//统计人事部员工人数
				if(this.getMyEmployee()[i].getEmployeeDep().getDepartmentNam().equals("市场部"))
				this.myEmployeeNum1+=1;//统计市场部员工人数
				return;
			}
		}
	}

测试类中我用的是员工去统计部门的人数：

public static void main(String[] args) {
		//实例化部门
		Department d1=new Department("部门01","人事部");
		Department d2=new Department("部门02","市场部");
		//实例化职务
		Post p1=new Post("职务01","经理");
		Post p2=new Post("职务02","助理");
		Post p3=new Post("职务03","职员");
		//实例化员工
		Employee e1=new Employee("S001","张铭","男",29,d1,p1);
		Employee e2=new Employee("S002","李艾爱","女",21,d1,p2);
		Employee e3=new Employee("S004","孙超","男",29,d1,p3);
		Employee e4=new Employee("S005","张美美","女",26,d2,p3);
		Employee e5=new Employee("S006","蓝迪","男",37,d2,p1);
		Employee e6=new Employee("S007","米莉","女",24,d2,p3);
		//调用addEmployee方法完成员工与部门的双向关联
		d1.addEmployee(e1);
		d1.addEmployee(e2);
		d1.addEmployee(e3);
		d2.addEmployee(e4);
		d2.addEmployee(e5);
		d2.addEmployee(e6);
		System.out.println("员工信息如下：");
		System.out.println(e1.introduction());
		System.out.println("=======================================");
		System.out.println(e2.introduction());
		System.out.println("=======================================");
		System.out.println(e3.introduction());
		System.out.println("=======================================");
		System.out.println(e4.introduction());
		System.out.println("=======================================");
		System.out.println(e5.introduction());
		System.out.println("=======================================");
		System.out.println(e6.introduction());
		System.out.println("=======================================");
		System.out.println("人事部总共有"+d1.getMyEmployeeNum()+"名员工！");
		System.out.println("市场部总共有"+d2.getMyEmployeeNum()+"名员工！");
		System.out.println("人事部总共有"+e2.getEmployeeDep().getMyEmployeeNum()+"名员工！");
		System.out.println("市场部总共有"+e6.getEmployeeDep().getMyEmployeeNum1()+"名员工！");
	}

但是实际上可以用部门来统计部门里的人数：

public static void main(String[] args) {
		//实例化部门
		Department d1=new Department("部门01","人事部");
		Department d2=new Department("部门02","市场部");
		//实例化职务
		Post p1=new Post("职务01","经理");
		Post p2=new Post("职务02","助理");
		Post p3=new Post("职务03","职员");
		//实例化员工
		Employee e1=new Employee("S001","张铭","hah",90,d1,p1);
		Employee e2=new Employee("S002","李艾爱","女",21,d1,p2);
		Employee e3=new Employee("S004","孙超","男",29,d1,p3);
		Employee e4=new Employee("S005","张美美","女",26,d2,p3);
		Employee e5=new Employee("S006","蓝迪","男",37,d2,p1);
		Employee e6=new Employee("S007","米莉","女",24,d2,p3);
		//调用addEmployee方法完成员工与部门的双向关联
		d1.addEmployee(e1);
		d1.addEmployee(e2);
		d1.addEmployee(e3);
		d2.addEmployee(e4);
		d2.addEmployee(e5);
		d2.addEmployee(e6);
		System.out.println("员工信息如下：");
		System.out.println(e1.introduction());
		System.out.println("=======================================");
		System.out.println(e2.introduction());
		System.out.println("=======================================");
		System.out.println(e3.introduction());
		System.out.println("=======================================");
		System.out.println(e4.introduction());
		System.out.println("=======================================");
		System.out.println(e5.introduction());
		System.out.println("=======================================");
		System.out.println(e6.introduction());
		System.out.println("=======================================");
		System.out.println("人事部总共有"+d1.getMyEmployeeNum()+"名员工！");
		System.out.println("市场部总共有"+d2.getMyEmployeeNum()+"名员工！");

我觉d1.getMyEmployeeNum(）与d2.getMyEmployeeNum()不好理解，我在代码中为什么只需要一个员工人数的属性即myEmployeeNum就可以统计，为什么部门间就能分别智能的统计，而不是一个3人一个6人得到的是累加的结果。希望老师解答一下，谢谢0.0！