如何检查用户是否按下了某个键？

Question

在java中，我有一个程序需要连续检查用户是否按下了某个键。 所以在伪代码中，类似

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

Answer 1

在 Java 中，您不会检查是否按下了某个键，而是“听”KeyEvent。 实现目标的正确方法是注册一个

KeyEventDispatcher

，并实现它来维持所需键的状态：

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;
                }
            }
        });
    }
}

那么您可以随时使用：

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

当然，您可以使用相同的方法来实现 

isPressing("<some key>")

，并将键映射及其状态封装在

IsKeyPressed

中。

Answer 2

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());
    }
}

Answer 3

我基于@Elist 的方法构建了一个方便的实用程序类，它适用于任何键。

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));

Answer 4

KeyListener

，看这里：

http://docs.oracle.com/javase/7/docs/api/java/awt/event/KeyListener.html

有关如何使用它的更多详细信息：

http://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html