Processing Streams

A processing stream operates on the data supplied by another stream. Often a processing stream acts as a buffer for the data coming from another stream. A buffer is a block of main memory used as a work area. For example, usually disks deliver their data in blocks of 512 bytes, no matter how few bytes a program has asked for. Usually the blocks of data are buffered and delivered to the program in the amounts it asks for.

In the following, the keyboard sends data to the InputStream System.in which is connected to a InputStreamReader stream which is connected to a BufferedReader stream. System.in is a stream object that the Java system automatically creates when your program starts running.

The data are transformed along the way. The raw bytes from the keyboard are grouped together into a String object that the program reads using stdin.readLine().

A program can set all this up by declaring a BufferedReader as follows:

BufferedReader stdin = 
    new BufferedReader( new  InputStreamReader( System.in ) );

This may seem like an unnecessary complication. But java.io gives you a collection of parts that can be assembled to do nearly any IO task you need.