Standard Streams

Some programs read the entire input stream is before they write the output stream. Other programs read the input stream item by item and produce one item of output for each item of input. There are many other patterns of input and output.

In general, a program may have several input streams flowing into it and several output streams flowing out of it. For most of the programs in these notes, there are three I/O streams:

• System.in — the input stream.
• System.out — the output stream for normal results.
• System.err — the output stream for error messages.

Normally System.in is connected to the keyboard and the data are characters. System.out and System.err both are connected to the monitor, and also are character data. These notes do not use System.err.