如何在主Java中调用功能Keypress

Question

so i've only this function keyPressed(KeyEvent e) in my class and i'm trying to call it in the main but it doesn't work. i know i should not initialize KeyEvent with null but i don't know how to call it

public void  keyPressed(KeyEvent e){
    int key = e.getKeyCode();

    switch(e.getKeyCode()) {

    case KeyEvent.VK_UP:
         break;
    case KeyEvent.VK_DOWN:
         break;
    case KeyEvent.VK_LEFT:
         break;
    case KeyEvent.VK_RIGHT:
         break;
}

public static void main(String args[]){
 Myclass class = new Myclass();
 KeyEvent KeyEvent = null;
 class.keyPressed(KeyEvent);
}

Answer 1

Update ^{(for this comment )} :

You'll get a NullPointerException inside your keyPressed(KeyEvent e) method because you haven't checked whether the passed argument is null or not before trying to access e.getKeyCode(); .

Try parsing an KeyEvent object

Myclass c = new Myclass();
KeyEvent ke = new KeyEvent(new Component() {}, 0, 0l, 0, KeyEvent.VK_UP);
c.keyPressed(ke);

---

Avoid using keywords as variable names. Try this,

Myclass c = new Myclass();
c.keyPressed(null);

Answer 2

You are sending a null value as a parameter to the function.

So It will surely crash at

     int key = e.getKeyCode();

with a NullPointerException since e is null bacuse you can't call getKeyCode() on a null object

Try passing a valid KeyEvent object as parameter

Eg:

public static void main(String args[]){
   Myclass myclass = new Myclass();
   KeyEvent KeyEvent = new KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_1);
   myclass.keyPressed(KeyEvent);
 }

Note: Replace new KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_1); with the code to find the keyEvent

Also if you want to prevent NullPointerException , put a null check in the keyPressed function as follows

 public void  keyPressed(KeyEvent e){
            if(e != null){
                int key = e.getKeyCode();

                switch(e.getKeyCode()) {

                case KeyEvent.VK_UP:
                     break;
                case KeyEvent.VK_DOWN:
                     break;
                case KeyEvent.VK_LEFT:
                     break;
                case KeyEvent.VK_RIGHT:
                     break;
            }
        }