The java.io Package - Reading and Writing Files

• FileStreams have three types of constructors
  1. a constructor that takes a filename as a String
  2. a constructor that takes a File object
  3. a constructor that takes a FileDescriptor object
• when constructors (1) or (2) are used, a new FileDescriptor object is created. This can be accessed by calling getFD()
• a FileDescriptor object represents a system-dependent value that describes an open file
• FileOutputStream has one additonal constructor

      FileOutputStream(String name, boolean append)
  

• if the file exists, you can set append to true to force the write to occur at the end of the file; otherwise, the existing file is overwritten
• FileOutputStream (and FileWriter) have a flush() method that forces the underlying buffer to be flushed.

• FileReader and FileWriter read and write 16-bit Unicode characters
• FileInputStream and FileOutputStream read and write bytes

Random Access Files (JPL pg 258)

• the RandomAccessFile class is NOT a subclass of InputStream, OutputStream, Reader or Writer; instead it incorporates all their functionaly plus additional methods by implementing the DataInput and DataOutput interfaces.

• the class has two constructors

      public RandomAccessFile(String name, String mode)
      public RandomAccessFile(File file, String mode)
  

• the mode argument must be either "r" or "rw" to indicate if the file is to be opened for reading only or reading and writing
• if the file is opened for writing and it does not exist; it will be created
• as with the other File streams, a FileDescriptor object is created when the file is opened
• the class allows you to set a read/write pointer to any position in the file
• key methods are:

      public long getFilePointer() throws IOException
      public void seek(long pos) throws IOException
      public void skipBytes(int count) throws IOException
      public long length() throws IOException
  

Source code examples

• Read a file using FileInputStream
  
• Write to a file using FileWriter
  
• Copy a file (jung.txt) to another file using FileReader and FileWriter
  
• An example, CopyBytes, to do the same thing using FileInputStream and FileOutputStream
• Test using a RandomAccessFile