Use keyPressed(), the function, instead of a check in draw().

Take a look at this post below for a very simple example of jump:
http://forum.processing.org/topic/i-need-help-30-7-2013

To test it online, go here:
http://studio.processingtogether.com/sp/pad/export/ro.9LZizxKsIAY4F/latest

Thanks GoToLoop, really interesting your example, I still have to fix that project.

For PhiLho, in another sketch

1. 
      
   void draw()
   {
   
     if( keyPressed )
     {
       if( key == 'd' )
       {
         motorcycle.accelerate();
       }
       if( key == 'a' )
       {
         motorcycle.slowDown();
       }
       if( key == 'w' )
       {
        motorcycle.jump();
     }

the function motorcycle.jump () is already draw (). How can I fix the problem?

thanks

For animations in general, callback input events (like mouse, keyboard, joypad)
should focus mainly in registering what happened only,
rather than also attempting to execute the action by themselves.

In my "Jump Example", variable dir acts as both a jump action flag and the speed for that.
So, when dir isn't zero, a jumping is taking place. Otherwise the object is on its "feet".

So the responsible code lines behave differently depending whether dir is zero or not:

• keyPressed() refuses to jump again.
• move() is called only when dir isn't zero.
• move() turns off dir back to zero to flag jump animation has completed.

Another online example. Not about jumping, but other movement actions:
http://studio.processingtogether.com/sp/pad/export/ro.9bY07S95k2C2a/latest