在Java中,我有一个程序需要持续检查用户是否按下了某个键。伪代码如下:
if (isPressing("w")) {
// do somthing
}
在Java中,你不需要检查按键是否被按下,而是要监听KeyEvent
事件。
实现你的目标的正确方式是注册一个KeyEventDispatcher
,并实现它来维护所需按键的状态:
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;
}
}
});
}
}
那么您总是可以使用:
if (IsKeyPressed.isWPressed()) {
// do your thing.
}
当然,你可以使用相同的方法来实现isPressing("<some key>")
,其中包含键和其状态的映射封装在IsKeyPressed
中。
IsKeyPressed.this
替换为IsKeyPressed.class
)。顺便说一句,在那种情况下,synchronized
块并不是真正必要的。 - ElistisWPressed()
,那么可能会出现缓存问题。使用volatile boolean
可能可以解决这个问题。 - Elist试试这个:
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());
}
}
我基于@Elist的方法构建了一个方便实用的工具类,可适用于任何键。
import java.awt.*;
import java.awt.event.KeyEvent;
import java.util.HashMap;
import java.util.Map;
public class Keyboard {
private static final Map<Integer, Boolean> pressedKeys = new HashMap<>();
static {
KeyboardFocusManager.getCurrentKeyboardFocusManager().addKeyEventDispatcher(event -> {
synchronized (Keyboard.class) {
if (event.getID() == KeyEvent.KEY_PRESSED) pressedKeys.put(event.getKeyCode(), true);
else if (event.getID() == KeyEvent.KEY_RELEASED) pressedKeys.put(event.getKeyCode(), false);
return false;
}
});
}
public static boolean isKeyPressed(int keyCode) { // Any key code from the KeyEvent class
return pressedKeys.getOrDefault(keyCode, false);
}
}
使用示例:
do {
if (Keyboard.isKeyPressed(KeyEvent.VK_W)) System.out.println("W is pressed!");
} while (!Keyboard.isKeyPressed(KeyEvent.VK_ESCAPE));
你需要实现 KeyListener
,可以在这里查看:
http://docs.oracle.com/javase/7/docs/api/java/awt/event/KeyListener.html
更多关于如何使用它的细节: http://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html