Mostly from the keyboard.
A program that reads input from the keyboard
can also read input from a file.
This is called
and is a feature of the command line interface
of most operating systems.
Say that you have a program
echo.java that writes to the monitor
what the user has typed.
Here is how the program usually works:
c:/> java echo Enter your input: User types this. You typed: User types this. c:/>
Without making any changes to the program you can do the following:
c:/> java echo < input.txt Enter your input: You typed: This is text from the file. c:/>
< input.txt" part
of the command line
connects the file
to the program and uses it as input in place of the keyboard.
In this example the file contained the characters
"This is text from the file."
input.txt must exist before the program is run.
Create it with a text editor.
Is input redirection a feature of Java or a feature of the operating system?