Input and Output

Streams

• In Java, I/O handled with streams.
• Think of a stream as a sequence of data flowing from one place to another (useful to think of as a buffer of data going one way or the other).
  • An input stream flows from an input source (e.g. keyboard, file) into a program, usually to be stored in variables
  • An output stream flows from a program to an output destination (e.g. screen, file, network socket)
• I/O libraries are in the package java.io
• Many built-in stream classes in Java, for processing different types of data. Two primary categories: byte streams and character streams
  • InputStream is the base class for byte stream input classes
  • OutputStream is the base class for byte stream output classes
  • Reader is the base class for character stream input classes
  • Writer is the base class for character stream output classes

Reading and Writing with Files

• File is a class used for checking properties of files.
• Basic File I/O classes.
  • FileInputStream - for byte streams
  • FileOutputStream - for byte streams
  • FileReader - for character streams
  • FileWriter - for character streams
• For the input streams, the primary method is called read. There is a version that reads one byte (or char), and a version that reads an array of bytes (or chars).
• For the output streams, the primary methods are called write. For writing single bytes (or chars) and for arrays of byte (or chars).

Example: CopyFileUsingByteStream.java -- example from text, which uses the file stream classes to copy one file to another

Buffered Streams

• Buffered streams help increase efficiency. They use a buffered array of bytes or characters. The buffered stream classes are:
  • BufferedInputStream - for byte streams
  • BufferedOutputStream - for byte streams
  • BufferedReader - for character streams
  • BufferedWriter - for character streams
• Buffered streams are used to add functionality to other streams (i.e. the buffering). Usually constructed out of other stream objects
• For example, to applied buffered streams to file i/o, we can create file streams, and then wrap them in a buffered stream object. Examples:

     BufferedReader infile1 = new BufferedReader(new FileReader(filename));
     BufferedOutputStream outfile1 = new BufferedOutputStream(new FileOutputStream(filename));
     Reader r1 = new BufferedReader(new FileReader("file1.txt"));
  

  Note that in the last declaration, the buffered reader object is attached to a Reader reference variable. This is legal since Reader is the base class for all reader classes

Examples

• Test1.java -- This program reads an input file and writes an all-uppercase copy of it to an output file. First argument is the input file, second argument is the output file.
• Test2.java -- This program reads an input file and counts the number of times a word appears. First argument is the input file, second argument is the word to search for.
• Test3.java -- This program uses some classes from the java.util package in addition to a file reader, and it lists all the words in the input file along with the number of times each word appears. The one command-line argument is the input file.
• Frost.txt -- here is a sample text file you can use to test each of these programs