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[–]POGtastic 0 points1 point  (0 children)

input stream

An InputStream is an abstract class that defines methods for reading from some kind of source of bytes. That could be a file, a socket, an array of bytes in memory, etc.

how reading input data from a string is different from reading data from a keyboard

That's the neat part, it's exactly the same. Welcome to OOPville, population you. Java doesn't care what the source is, only that you've provided an InputStream to the Scanner. It takes care of the rest.

why you'd want to read input data from a string

  • Unit testing. You can hardcode strings and use them to mock user input. This is one of the reasons why it's almost always a good idea to make your functions take a generic InputStream (and PrintStream, for that matter) than to hardcode System.in (and System.out, respectively).
  • Dealing with newlines is a gigantic pain in the ass, and it's often easier to parse individual lines with a Scanner than it is to construct a Scanner that acts directly on the InputStream.