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

Question

Is there an easy way to read a single char from the console as the user is typing it in Java  Is it possible  I ve tried with these methods but they all wait for the user to press enter key   char tmp    char  System in read    char tmp    char  new InputStreamReader System in  read     char tmp    char  System console   reader   read                 Java 6   I m starting to think that System in is not aware of the user input until enter is pressed

User · Accepted Answer

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.

User · Answer

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  lt  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

User · Answer

Use jline3   Example   Terminal terminal   TerminalBuilder builder        jna true       system true       build        raw mode means we get keypresses rather than line buffered input terminal enterRawMode    reader   terminal  reader        int read   reader read         reader close    terminal close

User · Answer

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

User · Answer

There is no portable way to read raw characters from a Java console   Some platform-dependent workarounds have been presented above  But to be really portable  you d have to abandon console mode and use a windowing mode  e g  AWT or Swing

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

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