I/O in Java

The sometimes confusing world of Java I/O

Java supports many kinds of I/O Streams.

Specialized by the type of data processed

• Byte streams read and write 8-bit bytes
  • InputStream
  • OutputStream
• Character streams read and write Unicode characters
  • Reader
  • Writer
• Data streams read and write primitive values and String objects
  • DataInput
  • DataOutput
• Object streams read and write Serializable objects
  • objectInput
  • objectOutput

Specialized by how the data is processed

• Methods of the Scanner classes break input into tokens.
  • Every serious web programmer needs to known how regular expressions, as implemented in Java’s Pattern class, can be used to tokenize input.
• Using format strings, output can be neatly written.
  • PrintWriter provides formatting for character output.
  • PrintStreams provides formatting for byte output.

What do we really have to know?

• System.out is a PrintStream.
• While System.in is only a InputStream, new Scanner(System.in) will create a Scaner for the “standard” input streams.
• new Scanner(new File("input.txt")) will open an input file and return a Scanner.
• new PrintWriter(new File("output.txt")) will open an output file and return a PrintWriter.

Java 1.7 and beyond

Starting with version 1.7, Java has a new package java.nio.file for handling file access. This package is much more sophiscated the the present java.io.file class. This new package is not used in the textbook, and we will not use it in class.

As far as I can I tell, you can use the following statement to open a file as a Scanner using the classes of the java.nio.file package.

new Scanner(FileSystems.getDefault().getPath("inFile.txt").toFile()) ;