// DataInputStream类实现了DataInput接口，要想从文件中读入二进制数据，

// 你需要将DataInputStream与某个字节源相结合，例如FileInputStream

// 与此同时，要想写出二进制数据，可以使用实现了DataOutput接口的DataOutputStream类

// RandomAccessFile类同时实现了DataInput和DataOutput接口。

// 以下程序将三条记录写到一个数据文件中，然后以逆序将它们从文件中读回。

// 为了高效地执行，这里需要使用随机访问，因为我们需要首先读入第三条记录

// 让我们来计算每条记录的大小：我们将使用40个字符来 表示姓名字符串，因此每条记录包含100个字节：

// 40字符 = 80字节，用于姓名

// 1 double = 8字节，用于薪水

// 3 int = 12字节，用于日期

package com.example.io;

import java.io.DataInput;

import java.io.DataOutput;

import java.io.DataOutputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.util.Calendar;

import java.util.Date;

import java.util.GregorianCalendar;

public class RandomFileTest {

    public static void main(String[] args) {

        Employee[] staff = new Employee[3];

        staff[0] = new Employee("Carl Cracker", 75000, 1987, 12, 15);

        staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);

        staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);

        try {

            // 保存所有雇员记录到文件当中

            DataOutputStream out = new DataOutputStream(new FileOutputStream("employee.dat"));

            for (Employee e : staff) {

                e.writeData(out);

            }

            out.close();

            // 读取所有记录到新数组中

            RandomAccessFile in = new RandomAccessFile("employee.dat", "r");

            // 计算数组的尺寸

            int n = (int) (in.length() / Employee.RECORD_SIZE);

            Employee[] newStaff = new Employee[n];

            //反序读入雇员记录

            for (int i = n - 1, j = 0; i >= 0; i--) {

                newStaff[j] = new Employee();

                in.seek(i * Employee.RECORD_SIZE);

                newStaff[j].readData(in);

                j++;

            }

            in.close();

            // 打印新读入数组记录内容

            for (Employee e : newStaff) {

                System.out.println(e);

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

}

class Employee {

    public Employee() {

    }

    public Employee(String n, double s, int year, int month, int day) {

        name = n;

        salary = s;

        GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);

        hireDay = calendar.getTime();

    }

    public String getName() {

        return name;

    }

    public double getSalary() {

        return salary;

    }

    public Date getHireDay() {

        return hireDay;

    }

    public void raiseSalary(double byPercent) {

        double raise = salary * byPercent / 100;

        salary += raise;

    }

    @Override

    public String toString() {

        return "Employee{" + "name=" + name + ", salary=" + salary + ", hireDay=" + hireDay + '}';

    }

    public void writeData(DataOutput out) throws IOException {

        DataIO.writeFixedString(name, NAME_SIZE, out);

        out.writeDouble(salary);

        GregorianCalendar calendar = new GregorianCalendar();

        calendar.setTime(hireDay);

        out.writeInt(calendar.get(Calendar.YEAR));

        out.writeInt(calendar.get(Calendar.MONTH) + 1);

        out.writeInt(calendar.get(Calendar.DAY_OF_MONTH));

    }

    public void readData(DataInput in) throws IOException {

        name = DataIO.readFixedString(NAME_SIZE, in);

        salary = in.readDouble();

        int y = in.readInt();

        int m = in.readInt();

        int d = in.readInt();

        GregorianCalendar calendar = new GregorianCalendar(y, m - 1, d);

        hireDay = calendar.getTime();

    }

    public static final int NAME_SIZE = 40;

    public static final int RECORD_SIZE = 2 * NAME_SIZE + 8 + 4 + 4 + 4;

    private String name;

    private double salary;

    private Date hireDay;

}

class DataIO {

    public static String readFixedString(int size, DataInput in) throws IOException {

        StringBuilder b = new StringBuilder(size);

        int i = 0;

        boolean more = true;

        while (more && i < size) {

            char ch = in.readChar();

            i++;

            if (ch == 0) {

                more = false;

            } else {

                b.append(ch);

            }

        }

        in.skipBytes(2 * (size - i));

        return b.toString();

    }

    public static void writeFixedString(String s, int size, DataOutput out) throws IOException {

        for (int i = 0; i < size; i++) {

            char ch = 0;

            if (i < s.length()) {

                ch = s.charAt(i);

            }

            out.writeChar(ch);

        }

    }

}