阅读和理解下面程序段 Class Manager extends employee { public Manager(String n,double s, int year, int month, int day) { super(n,s,year,month,day); bonys=0; } Public doub1e getSalary(); {doub1e baseSalary=super.getSalary();; return baseSalary+bonus; } Public void setBonys(doub1e b) {bonus=b; } Private doub1e bonus; } Manager 是Employee的子类,其理由是____