PrintWriter 和 Scanner 类的组合使用

Posted 2020-06-15

// 示例程序：将一个Employee记录数组存储成一个文本文件，其中每个记录都保存在单独的一行中，
// 而实例的域彼此之间使用分隔符分离开。
// 众所周知：
// 以二进制格式写出数据，需要使用DataOutputStream
// 以文本格式写出数据，需要使用PrintWriter
// 你可能认为存在着与DataOutputStream类似的类允许我们以文本格式读入数据，与此最接近的类是Scanner。
// 但在Java SE 5.0之前，处理文本输入的唯一方式就是通过BufferedReader类，它拥有一个readLine方法，
// 使得我们可以读入一行文本。你需要将带缓冲区的读入器与输入源组合起来：
// BufferedReader in = new BufferedReader(new FileReader("employee.txt"));
// readLine方法在没有输入时返回null。然而，一个典型的输入循环类似于这样：
// String line;
// while((line = in.readLine())!= null) {
// do something with line
// }
// 然而，BufferedReader没有任何用于读入数字的方法，建议使用Scanner来读入文本输入。
package com.example.io;

import java.io.FileReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Scanner;

public class TextFileTest {
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 {
PrintWriter out = new PrintWriter("employee.dat");
writeData(staff, out);
out.close();

Scanner in = new Scanner(new FileReader("employee.dat"));
Employee[] newStaff = readData(in);
in.close();

for (Employee e : newStaff) {
System.out.println(e);
}
} catch (IOException e) {
e.printStackTrace();
}
}

private static void writeData(Employee[] employees, PrintWriter out) throws IOException {
out.println(employees.length);
for (Employee e : employees) {
e.writeData(out);
}
}

private static Employee[] readData(Scanner in) {
int n = in.nextInt(); //读入数组长度
in.nextLine(); //消耗掉行尾的回车换行符

Employee[] employees = new Employee[n];
for (int i = 0; i < n; i++) {
employees[i] = new Employee();
employees[i].readData(in);
}
return employees;
}

}

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(PrintWriter out) {
GregorianCalendar calendar = new GregorianCalendar();
calendar.setTime(hireDay);
out.println(name + "|" + salary + "|" + calendar.get(Calendar.YEAR) + "|"
+ (calendar.get(Calendar.MONTH) + 1) + "|" + calendar.get(Calendar.DAY_OF_MONTH));
}

public void readData(Scanner in) {
String line = in.nextLine();
String[] tokens = line.split("\\|");//竖线在正则表达式中具有特殊的含义，因此需要用\字符来转义，而这个\又需要用另一个\来转义
name = tokens[0];
salary = Double.parseDouble(tokens[1]);
int y = Integer.parseInt(tokens[2]);
int m = Integer.parseInt(tokens[3]);
int d = Integer.parseInt(tokens[4]);
GregorianCalendar calendar = new GregorianCalendar(y, m - 1, d);
hireDay = calendar.getTime();
}
private String name;
private double salary;
private Date hireDay;
}