Java 对文件进行读写操作的例子很多，让初学者感到十分困惑，我觉得有必要将各种方法进行一次分析，归类，理清不同方法之间的异同点。一．在 JDK 1.0 中，通常是用 InputStream & OutputStream 这两个基类来进行读写操作的。InputStream 中的 FileInputStream 类似一个文件句柄，通过它来对文件进行操作，类似的，在 OutputStream 中我们有 FileOutputStream 这个对象。用FileInputStream 来读取数据的常用方法是：FileInputStream fstream = new FileInputStream(args[0]);DataInputStream in = new DataInputStream(fstream);用 in.readLine() 来得到数据，然后用 in.close() 关闭输入流。完整代码见 Example 1。用FileOutputStream 来写入数据的常用方法是：FileOutputStream out out = new FileOutputStream("myfile.txt"); PrintStream p = new PrintStream( out );用 p.println() 来写入数据，然后用 p.close() 关闭输入。完整代码见 Example 2。二．在 JDK 1.1中，支持两个新的对象 Reader & Writer, 它们只能用来对文本文件进行操作，而 JDK1.1中的 InputStream & OutputStream 可以对文本文件或二进制文件进行操作。用FileReader 来读取文件的常用方法是：FileReader fr = new FileReader("mydata.txt");BufferedReader br = new BufferedReader(fr); 用 br.readLing() 来读出数据，然后用br.close() 关闭缓存，用fr.close() 关闭文件。完整代码见 Example 3。 用 FileWriter 来写入文件的常用方法是：FileWriter fw = new FileWriter("mydata.txt");PrintWriter out = new PrintWriter(fw); 在用out.print 或 out.println 来往文件中写入数据，out.print 和 out.println的唯一区别是后者写入数据或会自动开一新行。写完后要记得 用out.close() 关闭输出，用fw.close() 关闭文件。 完整代码见 Example 4。-------------------------------------------------------------- following is the source code of examples------------------------------------------------------Example 1:// FileInputDemo// Demonstrates FileInputStream and DataInputStreamimport java.io.*;class FileInputDemo { public static void main(String args[]) { // args.length is equivalent to argc in C if (args.length == 1) { try { // Open the file that is the first command line parameter FileInputStream fstream = new FileInputStream(args[0]); // Convert our input stream to a DataInputStream DataInputStream in = new DataInputStream(fstream); // Continue to read lines while there are still some left to read while (in.available() !=0) { // Print file line to screen System.out.println (in.readLine()); } in.close(); } catch (Exception e) { System.err.println("File input error"); } } else System.out.println("Invalid parameters"); }}Example 2:// FileOutputDemo// Demonstration of FileOutputStream and PrintStream classesimport java.io.*;class FileOutputDemo { public static void main(String args[]) { FileOutputStream out; // declare a file output object PrintStream p; // declare a print stream objecttry { // connected to "myfile.txt" out = new FileOutputStream("myfile.txt"); // Connect print stream to the output stream p = new PrintStream( out ); p.println ("This is written to a file"); p.close(); } catch (Exception e) { System.err.println ("Error writing to file"); } }}Example 3:// FileReadTest.java// User FileReader in JDK1.1 to read a file import java.io.*;class FileReadTest { public static void main (String[] args) { FileReadTest t = new FileReadTest(); t.readMyFile();} void readMyFile() { String record = null; int recCount = 0; try { FileReader fr = new FileReader("mydata.txt"); BufferedReader br = new BufferedReader(fr); record = new String(); while ((record = br.readLine()) != null) { recCount++; System.out.println(recCount + ": " + record); }br.close();fr.close(); } catch (IOException e) { System.out.println("Uh oh, got an IOException error!"); e.printStackTrace(); }} } Example 4:// FileWriteTest.java// User FileWriter in JDK1.1 to writer a file import java.io.*;class FileWriteTest { public static void main (String[] args) { FileWriteTest t = new FileWriteTest(); t.WriteMyFile();} void WriteMyFile() { try { FileWriter fw = new FileWriter("mydata.txt");PrintWriter out = new PrintWriter(fw); out.print(“hi,this will be wirte into the file!”); out.close();fw.close(); } catch (IOException e) { System.out.println("Uh oh, got an IOException error!"); e.printStackTrace(); }} }
