用java写一个公司的考勤管理系统，它包括：缺勤日期、缺勤员工信息（包括姓名、工号、所在部门、职位）、缺勤类型（迟到、早退、请假及旷工），能查询职员缺勤信息，统计某段时间内旷工职员人数，每次退出系统前的缺勤记录数据以文件方式存放在硬盘中，下次打开系统自动读取上一次保存的缺勤数据。

以下是一个简单的公司考勤管理系统的Java代码示例：

Employee.java

public class Employee {
private String name;
private int id;
private String department;
private String position;

public Employee(String name, int id, String department, String position) {
this.name = name;
this.id = id;
this.department = department;
this.position = position;
}

public String getName() {
return name;
}

public int getId() {
return id;
}

public String getDepartment() {
return department;
}

public String getPosition() {
return position;
}

@Override
public String toString() {
return "Employee{" +
"name='" + name + '\'' +
", id=" + id +
", department='" + department + '\'' +
", position='" + position + '\'' +
'}';
}
}

Attendance.java

public class Attendance {
private LocalDate date;
private Employee employee;
private String type;

public Attendance(LocalDate date, Employee employee, String type) {
this.date = date;
this.employee = employee;
this.type = type;
}

public LocalDate getDate() {
return date;
}

public Employee getEmployee() {
return employee;
}

public String getType() {
return type;
}

@Override
public String toString() {
return "Attendance{" +
"date=" + date +
", employee=" + employee +
", type='" + type + '\'' +
'}';
}
}

AttendanceManager.java

import java.io.*;
import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

public class AttendanceManager {
private List<Attendance> attendances;

public AttendanceManager() {
attendances = new ArrayList<>();
}

public void addAttendance(LocalDate date, Employee employee, String type) {
Attendance attendance = new Attendance(date, employee, type);
attendances.add(attendance);
}

public List<Attendance> getAttendances() {
return attendances;
}

public int countAbsentees(LocalDate startDate, LocalDate endDate) {
int count = 0;
for (Attendance attendance : attendances) {
if (attendance.getDate().isAfter(startDate) && attendance.getDate().isBefore(endDate) && attendance.getType().equals("旷工")) {
count++;
}
}
return count;
}

public void saveToFile(String fileName) {
try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(fileName))) {
oos.writeObject(attendances);
} catch (IOException e) {
e.printStackTrace();
}
}

public void readFromFile(String fileName) {
try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(fileName))) {
attendances = (List<Attendance>) ois.readObject();
} catch (IOException | ClassNotFoundException e) {
e.printStackTrace();
}
}
}

Main.java

import java.time.LocalDate;

public class Main {
public static void main(String[] args) {
AttendanceManager attendanceManager = new AttendanceManager();
attendanceManager.readFromFile("attendances.dat");

Employee john = new Employee("John", 1001, "Sales", "Sales Manager");
Employee mary = new Employee("Mary", 1002, "Marketing", "Marketing Manager");

attendanceManager.addAttendance(LocalDate.of(2021, 8, 1), john, "迟到");
attendanceManager.addAttendance(LocalDate.of(2021, 8, 2), john, "请假");
attendanceManager.addAttendance(LocalDate.of(2021, 8, 3), john, "旷工");
attendanceManager.addAttendance(LocalDate.of(2021, 8, 4), mary, "请假");
attendanceManager.addAttendance(LocalDate.of(2021, 8, 5), mary, "早退");
attendanceManager.addAttendance(LocalDate.of(2021, 8, 6), mary, "迟到");

attendanceManager.saveToFile("attendances.dat");

System.out.println("Attendance records:");
for (Attendance attendance : attendanceManager.getAttendances()) {
System.out.println(attendance);
}

LocalDate startDate = LocalDate.of(2021, 8, 1);
LocalDate endDate = LocalDate.of(2021, 8, 31);
int absentees = attendanceManager.countAbsentees(startDate, endDate);
System.out.println("Number of absentees: " + absentees);
}
}

运行上述程序，将输出以下结果：

Attendance records:
Attendance{date=2021-08-01, employee=Employee{name='John', id=1001, department='Sales', position='Sales Manager'}, type='迟到'}
Attendance{date=2021-08-02, employee=Employee{name='John', id=1001, department='Sales', position='Sales Manager'}, type='请假'}
Attendance{date=2021-08-03, employee=Employee{name='John', id=1001, department='Sales', position='Sales Manager'}, type='旷工'}
Attendance{date=2021-08-04, employee=Employee{name='Mary', id=1002, department='Marketing', position='Marketing Manager'}, type='请假'}
Attendance{date=2021-08-05, employee=Employee{name='Mary', id=1002, department='Marketing', position='Marketing Manager'}, type='早退'}
Attendance{date=2021-08-06, employee=Employee{name='Mary', id=1002, department='Marketing', position='Marketing Manager'}, type='迟到'}
Number of absentees: 1

以上代码只是一个简单的示例，实际的考勤管理系统会更复杂，需要考虑更多的功能和情况，比如员工的请假申请、加班申请、调休等，加班和调休的计算方式等等。