玻璃杯中的花生壳--Java中对文件的读写操作之比较

[java]Java中对文件的读写操作之比较

[ 2006/8/10 14:58:06 | By: 玻璃杯中的花生壳 ]

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 Cif (args.length == 1) {try {// Open the file that is the first command line parameterFileInputStream fstream = new FileInputStream(args[0]);// Convert our input stream to a DataInputStreamDataInputStream in = new DataInputStream(fstream);// Continue to read lines while there are still some left to readwhile (in.available() !=0) {// Print file line to screenSystem.out.println (in.readLine());}in.close();} catch (Exception e) {System.err.println("File input error");}}elseSystem.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 objectPrintStream p; // declare a print stream objecttry {// connected to "myfile.txt"out = new FileOutputStream("myfile.txt");// Connect print stream to the output streamp = 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 fileimport 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 fileimport 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();}}}

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