That's a kind of FAQ, you can search the forum.
Basically, in keyPressed(), you set a boolean (one variable per key you watch) to true, and in keyReleased(), you reset it to false.
Then in draw(), you make conditions based on these booleans to do what you need.

Hard to be more precise as you don't show code.

Thanks PhiLho for your response!

Here is a piece of code I wrote.. I deleted what I considered as unnecessary!

As I said the only thing I want is to be able to shoot (by pressing the space bar) without causing the craft to stop..

Thanks!

#############################################################################
Craft craft; // Create a new Craft/Spaceship
int isFired;

void setup() {
  size(700, 400);
  background(128);
  craft = new Craft(width/2, height/2);
}

void draw() {
  background(128);
  craft.display();

  if (buttonUp == 48 || (keyPressed==true && keyCode==UP)) {
    craft.goUp();
  }
  if (buttonDown == 48 || (keyPressed==true && keyCode==DOWN)) {
    craft.goDown();
  }
  if (buttonLeft == 48 || (keyPressed==true && keyCode==LEFT)) {
    craft.goLeft();
  }
  if (buttonRight == 48 || (keyPressed==true && keyCode==RIGHT)) {
    craft.goRight();
  }
  if (rocket.isFired==1) {
    rocket.fire(temp_rocket_Ypos, craft.direction);
  }
}

void keyPressed() {
  if (keyCode==32) {
    rocket.isFired=1;
  }
}
#############################################################################

As I wrote, move your test around keyPressed == true (a quite redundant test) to keyPressed(), and manage keyReleased() too.
And as I wrote, if you search the forum with keywords like keypressed keyreleased boolean multiple, you can find topics like this one: https://forum.processing.org/topic/help-with-key-variable

Thanks PhiLho!

Your help is incredible! I really love it when your reply contains fully working code!


The question is..


What if I want to use "space bar" instead of "control"?

I tried to replace "control" with "32" but does not work but if I replace it with 17 (which is control) it works..

Any ideas ?


Thank you again!

Ok I fixed by adding an

 else if(keyCode==32){
  spacebar=true;
  }

Here, spacebar is my boolean variable which I use as the kU, kd etc as you showed me!



Thanks!

Actually, my first version was like that.
But I found out that when moving in diagonal, I cannot fire (except, curiously, for up/right moves), for some unknown reason. So I switched to Control instead...

Yeah I have the exact same problem..

I have something in my mind that may fix it.. I 'll let you know if something good happens..

Thanks again!