Collecting characters from the keyboard is done by the operating system. While this is going on, the Java program is suspended. The user can edit the line, and then hit "enter" to signal that it is complete. Only then does the Java program see the characters and resume execution.

Here is another run of the program:

Notice that the characters '1', '4', '9', and '2' were read in and written out just as were the other characters.

Now consider yet another run:

Nothing special here. The '1', '4', '9', and '2' are just characters. A String object is created, and those characters are stored in the object, just like any characters. If you want the user to enter numeric data, your program must convert from character data to a numeric type.