Responding directly to your title, keyPressed() is only called when a key is pressed... you need keyReleased() to pick up key releases... perhaps what you are looking for is multiple key presses?

Thank you for your reply.

You have events when a key is pressed or released. Just use that. You know A is still down because it hasn't been released. With a few booleans, you can track the current state of the keys you want to monitor.

Well,  it is not event-driven.

" it is not event-driven"
Not sure what is "it".
keyPressed() and friends are event driven. Not directly, the events are actually queued, but the queuing is event driven.

These events doesn't work how you think they should...
" I want to got "pressed 65535 37" after key RIGHT released if the key LEFT not release"
LEFT isn't pressed again. Pressed means it goes from up to down. But LEFT is just down.
You expect a state, but as I wrote, these are events.
And as I wrote, you have to use booleans to manage the states yourself.
OK, here is a simple demonstration:

1. // States
2. boolean aIsDown, bIsDown;
3.  
4. // Events
5. void keyPressed()
6. {
7.   if (key == 'a') aIsDown = true;
8.   if (key == 'b') bIsDown = true;
9. }
10.  
11. void keyReleased()
12. {
13.   if (key == 'a') aIsDown = false;
14.   if (key == 'b') bIsDown = false;
15. }
16.  
17. void setup()
18. {
19.   size(400, 200);
20. }
21.  
22. void draw()
23. {
24.   if (aIsDown) fill(#FF0000);
25.   else fill(#FFFF00);
26.   ellipse(100, 100, 75, 75);
27.  
28.   if (bIsDown) fill(#FF0000);
29.   else fill(#FFFF00);
30.   ellipse(200, 100, 75, 75);
31. }

I know it works. But If you always key down one key not release. The keypressed will be called again and again till it released.

" The keypressed will be called again and again till it released."
Ah, that! Indeed, that's a system thing, that's the auto-repeat of your keyboard, which you can see when you leave a key pressed in your message window... I don't think that's a problem, is it?

" it will response just what they need response"
I am not sure of what that means. What is "it", "they" and what is a "response"? Perhaps some code (like the simple one I shown) can illustrate your problem.

" If I need more key to flag, management will be so hard."
Not really, if you use an array.

" I don't want to care about the specific key."
Well, I fear I failed to understand what you plan to do then.

Thank you very much indeed!