Java 源码 ——顺序存取文件的创建及写入（Writing data to a sequential text file with class Formatter）

代码如下：

// Fig. 15.3: CreateTextFile.java// Writing data to a sequential text file with class Formatter.package ch15;import java.io.FileNotFoundException;     import java.lang.SecurityException;       import java.util.Formatter;               import java.util.FormatterClosedException;import java.util.NoSuchElementException;  import java.util.Scanner;                 public class CreateTextFile{   private static Formatter output; // outputs text to a file          public static void main(String[] args)   {      openFile();      addRecords();      closeFile();   }    // open file clients.txt   public static void openFile()   {      try      {         output = new Formatter("clients.txt"); // open the file      }      catch (SecurityException securityException)      {         System.err.println("Write permission denied. Terminating.");         System.exit(1); // terminate the program      }       catch (FileNotFoundException fileNotFoundException)      {         System.err.println("Error opening file. Terminating.");         System.exit(1); // terminate the program      }    }    // add records to file   public static void addRecords()   {      Scanner input = new Scanner(System.in);      System.out.printf("%s%n%s%n? ",          "Enter account number, first name, last name and balance.",         "Enter end-of-file indicator to end input.");      while (input.hasNext()) // loop until end-of-file indicator      {         try         {            // output new record to file; assumes valid input            output.format("%d %s %s %.2f%n", input.nextInt(),               input.next(), input.next(), input.nextDouble());                                      }          catch (FormatterClosedException formatterClosedException)         {            System.err.println("Error writing to file. Terminating.");            break;         }          catch (NoSuchElementException elementException)         {            System.err.println("Invalid input. Please try again.");            input.nextLine(); // discard input so user can try again         }          System.out.print("? ");      }   }   // close file   public static void closeFile()   {      if (output != null)         output.close();   } } // end class CreateTextFile

测试结果：

1. 正常

Enter account number, first name, last name and balance.
Enter end-of-file indicator to end input.
? 101 Honglei Li 898.99
? 102 Facai Yao 999.58
? 106 Yongjiu Niu 1058.99
? ^Z

2. 异常

将clients.txt文件更改为read only，运行程序，报错：

Error opening file. Terminating.

文件操作还是很有意思的！:)