How do I check if the user is pressing a key?

问题:

In java I have a program that needs to check continuously if a user is pressing a key. So In psuedocode, somthing like

if (isPressing(\"w\"))
{
 //do somthing
}

Thanks in advance!

回答1:

In java you don\'t check if a key is pressed, instead you listen to KeyEvents. The right way to achieve your goal is to register a KeyEventDispatcher, and implement it to maintain the state of the desired key:

import java.awt.KeyEventDispatcher;
import java.awt.KeyboardFocusManager;
import java.awt.event.KeyEvent;

public class IsKeyPressed {
    private static volatile boolean wPressed = false;
    public static boolean isWPressed() {
        synchronized (IsKeyPressed.class) {
            return wPressed;
        }
    }

    public static void main(String[] args) {
        KeyboardFocusManager.getCurrentKeyboardFocusManager().addKeyEventDispatcher(new KeyEventDispatcher() {

            @Override
            public boolean dispatchKeyEvent(KeyEvent ke) {
                synchronized (IsKeyPressed.class) {
                    switch (ke.getID()) {
                    case KeyEvent.KEY_PRESSED:
                        if (ke.getKeyCode() == KeyEvent.VK_W) {
                            wPressed = true;
                        }
                        break;

                    case KeyEvent.KEY_RELEASED:
                        if (ke.getKeyCode() == KeyEvent.VK_W) {
                            wPressed = false;
                        }
                        break;
                    }
                    return false;
                }
            }
        });
    }
}

Then you can always use:

if (IsKeyPressed.isWPressed()) {
    // do your thing.
}

You can, of course, use same method to implement isPressing(\"<some key>\") with a map of keys and their state wrapped inside IsKeyPressed.

回答2:

Try this:

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;

public class Main {

    public static void main(String[] argv) throws Exception {

    JTextField textField = new JTextField();

    textField.addKeyListener(new Keychecker());

    JFrame jframe = new JFrame();

    jframe.add(textField);

    jframe.setSize(400, 350);

    jframe.setVisible(true);

}

class Keychecker extends KeyAdapter {

     @Override
     public void keyPressed(KeyEvent event) {

     char ch = event.getKeyChar();

     System.out.println(event.getKeyChar());

}

回答3:

You have to implement KeyListener,take a look here: http://docs.oracle.com/javase/7/docs/api/java/awt/event/KeyListener.html

More details on how to use it: http://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html