Why can't we read one character at a time from System.in?

user_276052 0
Viewed 12004

The program below prints each character written on standard in, but only after a new-line has been written (at least on my system!).

public class Test {
    public static void main(String[] args) throws java.io.IOException {
        int c;
        while ((c = System.in.read()) != -1)
            System.out.print((char) c);
    }
}

This prevents people from writing stuff like "Press any key to continue" and forces something like "Press enter to continue."

  • What is the underlying reason for this?
  • Is it a limitation of Java?
  • Is this behavior system-dependent (I'm on Ubuntu)? How does it work on Mac? Windows?
  • Is it dependent on the specific terminal I run the application in? (For me it behaves like this in Eclipse and in gnome-terminal)
  • Is there a workaround?
stdin java
3 Answers

see my answer in Equivalent function to C's "_getch()" in Java?


public static void getCh() {


    final JFrame frame = new JFrame();

    synchronized (frame) {

        frame.setUndecorated(true);

        frame.getRootPane().setWindowDecorationStyle(JRootPane.FRAME);

        frame.addKeyListener(new KeyListener() {

            public void keyPressed(KeyEvent e) {

                synchronized (frame) {

                    frame.setVisible(false);

                    frame.dispose();

                    frame.notify();

                }

            }  



        public void keyReleased(KeyEvent e) {  
        }  

        public void keyTyped(KeyEvent e) {  
        }  
    });  
    frame.setVisible(true);  
    try {  
        frame.wait();  
    } catch (InterruptedException e1) {  
    }  
}

}

user_10617860
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