J2ME Controls LEFT and UP

Question

I'm trying to make a 2d game using java microedition and i just want to make my control smoother but the problem is when i press the LEFT key while pressing the UP Key the condition is not working i dont know why

public void moveJet2() throws IOException{
     int gameAction = getKeyStates();

     if(gameAction==LEFT_PRESSED && gameAction==UP_PRESSED){
         padX-=padXVel;
         padY-=padYVel;
     }
     else if(gameAction==RIGHT_PRESSED){
         padX += padXVel;
     }
     else if(gameAction==UP_PRESSED){
         padY-=padYVel;
     }
     else if(gameAction==DOWN_PRESSED){
         padY+=padYVel;
     }            
}

score 1 · Accepted Answer · answered Oct 02 '16 at 15:56

getKeyStates() returns the state of keys in a single int. The various keys have individual values. UP_PRESSED = 0x0002 and LEFT_PRESSED = 0x0004. So if you press UP on your d-pad while calling getKeyStates(), you'll get 2 back, and if (getKeyStates()==UP_PRESSED) will thus be true. Likewise, if you press LEFT on your d-pad while calling getKeyStates(), you'll get 4 back.

But if you press UP and LEFT at the same time, you can't get back 2 and 4 - because that's obviously 2 ints - and getKeyStates() only returns one int.

What you do get back though, is rather simple: 2 + 4 = 6. So, asking if (getKeyStates()==6) will be true if pressing UP and LEFT at the same time. Or if (getKeyStates()==UP_PRESSED+LEFT_PRESSED).

Typically though, you would ask using bit-operators, like this:

public void moveJet2() throws IOException{
 int gameAction = getKeyStates();

 if((gameAction & LEFT_PRESSED)!=0) {
  padX -= padXVel;
 }
 if((gameAction & RIGHT_PRESSED)!=0) {
  padX += padXVel;
 }
 if((gameAction & UP_PRESSED)!=0) {
  padY-=padYVel;
 }
 if((gameAction & DOWN_PRESSED)!=0){
  padY+=padYVel;
 }            
}

Because using that approach will work with any of the 8 directions you can press at the same time.

Thank you so much Mister :) – xFaceless Oct 02 '16 at 21:09 — xFaceless, Oct 02 '16 at 21:09

J2ME Controls LEFT and UP

1 Answers1