File Processing

In Java, reading from files and writing to files are handled using streams. Any operation can throw an exception.

A file opened for writing must be closed before it can be opened for reading, or vice versa.

Writing

import java.io.*;

class WriteAFile {
  public static void main (String[] args) {
    try {
      FileWriter writer = new FileWriter(“foo.txt”); // creates foo.txt if doesn't exist
      writer.write(“hello foo!”);
      writer.close(); // if not closed, when the program ends abnormally, the file might get corrupt
    } catch(IOException ex) {
      ex.printStackTrace();
    }
  }
}

Reading

import java.io.*;

class ReadAFile {
  public static void main (String[] args) {
    try {
      FileReader reader = new FileReader("foo.txt");
      BufferedReader bufferedReader = new BufferedReader(reader);

      String line;
      while ((line = bufferedReader.readLine()) != null) {
        System.out.println(line);
      }
      bufferedReader.close();
    } catch(IOException ex) {
      ex.printStackTrace();
    }
  }
}

Buffering

By default, in Java, each byte is read/written from/to disk as soon as possible. Each byte will have a little delay as the disk operations are slower. Causes performance issues.

Buffering is a solution. Instead of reading/writing from/to disk instantly, the data is read/written in chunks. A buffer (fixed-length memory) is allocated for temporarily storing the chunk. When writing, disk is accessed only when the buffer is full. When reading, the operation have to wait until the chunk is filled from the disk.

BufferedReader and BufferedWriter can be used for this purpose.