Java easiest keylistener

Question

I know there was milions of questions about that, but I can't understand most of them. I've seen that people make something like that:

public void keyPressed(KeyEvent e)
{
    if (e.getKeyCode()== KeyEvent.VK_Q)
        //do something
}

but keyPressed must override methos of some class to work or be runned in other thread. I really don't know how to do that. Can someone give me code of the easiest keylistener for java.
It should work even when program is not focused (it's just console program).

import java.awt.AWTException;
import java.awt.Robot;
import java.awt.event.*;

import javax.swing.JFrame;

public class SquatCounter {

class MyKeyListener extends KeyAdapter{
    public void keyPressed(KeyEvent e)
    {
        if (e.getKeyCode()== KeyEvent.VK_Q)
            System.out.println("Key Q pressed!");
    }
}

JFrame jf = new JFrame("title");
public SquatCounter() {
    jf.addKeyListener(new MyKeyListener());
}
public static void main(String[] args) {
    Key1 key = new Key1 ();
    SquatCounter test = new SquatCounter();
}
}

If it's a console program, I don't think a KeyListener will help you. Can you tell us more about why you think you need a KeyListener? What problem are you really trying to solve? — dnault, Jan 18 '16 at 21:49
Possible duplicate of [How to read a single char from the console in Java (as the user types it)?](http://stackoverflow.com/questions/1066318/how-to-read-a-single-char-from-the-console-in-java-as-the-user-types-it) — dnault, Jan 18 '16 at 21:51
KeyListener is part of Swing which means GUI not console. What are you really trying to accomplish? — Pshemo, Jan 18 '16 at 21:52
There is a tutorial https://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html about implementing key listeners. — nolexa, Jan 18 '16 at 21:53
I don't want to type anything in console. I want make something like game hack? I want to turn it's functions on and off while playing. — Konrad, Jan 18 '16 at 21:59
Then, as stated, `KeyListener` is useless for you. You want to keep an open input stream. — user1803551, Jan 18 '16 at 23:41
Look [here](http://stackoverflow.com/q/30564519/1803551) and [here](http://stackoverflow.com/q/1066318/1803551). — user1803551, Jan 19 '16 at 16:03

sguan · Accepted Answer · 2016-01-18T22:25:20.523

When you setup the JFrame, add a KeyListener like this:

JFrame jf = new JFrame("title");
jf.addKeyListener(new MyKeyListener());
jf.setVisible(false);

(The jf.setVisible(false); stops the program window from appearing (only command line)

Then create a new class called MyKeyListener that extends KeyAdapter.

class MyKeyListener extends KeyAdapter{
    public void keyPressed(KeyEvent e)
    {
        if (e.getKeyCode()== KeyEvent.VK_Q)
            System.out.println("Key Q pressed!");
    }
}

Now let me explain things a bit.

First, when you create a JFrame, it has no default KeyListener attached. Therefore, we have to create a class MyKeyListener to do that.

Secondly, we extended KeyAdapter instead of implementing KeyListener because there are a lot more methods than what you need in there. You only need to override the keypressed() method when you extends KeyAdapter but you have to implement all (I think it's 3) the other methods that you don't need for your purposes.

Lastly, if you want to do other methods like keyreleased(), just add it in to the MyKeylistener class and it will work.

Hope this helps!

EDIT: Per OP's request, it should be like this:

BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String line = "";

while (line.equalsIgnoreCase("q") == false) {
   line = in.read();

   System.out.println("Q is pressed!");
}

in.close();

I see what you try to tell me, but is it possible to have something like keylistener without program window? — Konrad, Jan 18 '16 at 22:01
I did as you wrote, but is seems not to work. Need I call that method or something? I made that class in my main class. — Konrad, Jan 18 '16 at 22:07
The OP wants a console program, not Swing. Besides, hiding the frame will not allow it to receive any key events. — user1803551, Jan 18 '16 at 23:37

score 0 · Answer 2 · edited May 23 '17 at 12:04

Just add a KeyListener.

import java.awt.AWTException;
import java.awt.Robot;
import java.awt.event.*;

import javax.swing.JFrame;

public class SquatCounter {
    JFrame jf = new JFrame("title") {{
        setVisible(true);
        setDefaultCloseOperation(3); // EXIT_ON_CLOSE
    }};

    public SquatCounter() {
        jf.addKeyListener(new KeyListener() {
            @Override
            public void keyPressed(KeyEvent event) {
                if (e.getKeyCode()== KeyEvent.VK_Q)
                    //do something
            }
            @Override
            public void keyReleased(KeyEvent event) {
                // different stuff
            }
            @Override
            public void keyTyped(KeyEvent event) {
                // more stuff
            }
        });
    }

    public static void main(String[] args) {
        SquatCounter test = new SquatCounter();
    }
}

Doing something out of focus has an answer here: Stackoverflow: Listening for input without focus in Java

Um, I don't think so, it wouldn't make much sense if it did, but I'm not 100% sure. — John S., Jan 18 '16 at 22:49
The OP wants a console program, not Swing. Besides, hiding the frame will not allow it to receive any key events. — user1803551, Jan 18 '16 at 23:38

Java easiest keylistener

2 Answers2