Java's Object Orientation, I/O

CS 161 - Java

Attaching / Stacking Streams

An easy way to improve performance: Use Java's capability to attach one stream to another.

Source: examples/BufferedCopy.java



/** Copy file contents using buffering

 **/

 

import java.io.BufferedReader;

import java.io.FileReader;

import java.io.BufferedWriter;

import java.io.FileWriter;

import java.io.IOException;

 

public class BufferedCopy {

  public static void main(String[] args) {

    if (args.length != 1)

      System.out.println("usage: BufferedCopy file_to_copy");

    else {

      BufferedCopy obj = new BufferedCopy();

      try {

        obj.makeCopy(args[0]);

      }

      catch (IOException e) {

        System.out.println(e);

      }

    }

  }

 

  public void makeCopy(String filename) throws IOException {

    FileReader fr = new FileReader(filename);

    BufferedReader bufIn = new BufferedReader(fr);

 

    FileWriter fw = new FileWriter(filename + ".copy");

    BufferedWriter bufOut = new BufferedWriter(fw);

 

    // An alternative way to write the previous four lines is:

    // BufferedReader bufIn = new BufferedReader( new FileReader(args[0]));

    // BufferedWriter bufOut = new BufferedWriter( new FileWriter(filename + "copy));

    // since fr and fw are only used in the BufferedReader/Writer

    // constructors.  

 

    String s;

 

    // Read and write lines of text (through buffers) 

    while (true) {

      s = bufIn.readLine();             // trims end of line character

      if (s == null)

        break;

      bufOut.write(s);

      bufOut.newLine();                 // adds an end of line character

    }

 

    // Flush anything remaining and release resouurces

    bufIn.close();

    bufOut.close();

    bufIn = null;

    bufOut = null;

  }

}

Buffered input also enables some other capabilities that would not be possible otherwise, e.g., readLine().

Question: Why isn't readLine() implemented for other Stream and Reader classes?

Other Stream and Reader/Writer classes provide other useful filters.

Question: What's the point of the alternative way of creating in and out?

jwd