How to read a single char from the console in Java (as the user types it)?

You need to knock your console into raw mode. There is no built-in platform-independent way of getting there. jCurses might be interesting, though.

On a Unix system, this might work:

String[] cmd = {"/bin/sh", "-c", "stty raw </dev/tty"};
Runtime.getRuntime().exec(cmd).waitFor();

For example, if you want to take into account the time between keystrokes, here's sample code to get there.

What you want to do is put the console into "raw" mode (line editing bypassed and no enter key required) as opposed to "cooked" mode (line editing with enter key required.) On UNIX systems, the 'stty' command can change modes.

Now, with respect to Java... see Non blocking console input in Python and Java. Excerpt:

If your program must be console based, you have to switch your terminal out of line mode into character mode, and remember to restore it before your program quits. There is no portable way to do this across operating systems.

One of the suggestions is to use JNI. Again, that's not very portable. Another suggestion at the end of the thread, and in common with the post above, is to look at using jCurses.

I have written a Java class RawConsoleInput that uses JNA to call operating system functions of Windows and Unix/Linux.

• On Windows it uses _kbhit() and _getwch() from msvcrt.dll.
• On Unix it uses tcsetattr() to switch the console to non-canonical mode, System.in.available() to check whether data is available and System.in.read() to read bytes from the console. A CharsetDecoder is used to convert bytes to characters.

It supports non-blocking input and mixing raw mode and normal line mode input.