Collision detection then get player to stop

Question

I am using processing and I would like to create a game where the player is in a room and if they hit a wall they stop moving like a normal wall. However I don't really have any idea how to do this. With my current method once they hit the wall they can't move on the x axis anymore. Any help would be greatly appreciated.

PVector playerPosition;
PVector barrierPosition;

float velocity = 4;

boolean goLeft=false;
boolean goRight=false;
boolean goUp=false;
boolean goDown=false;

float playerWidth = 10;
float playerHeight = 10;

float barrierWidth = 10;
float barrierHeight = 600;



void setup() {
  size(800,600);
  rectMode(CORNER);
  playerPosition = new PVector(200,200);
  barrierPosition = new PVector(0,0);
}

void draw() {
 background(255); 
 drawPlayer();
 movePlayerPosition();
 drawBarrier();
 checkCollide();



}
  //check for collision with barrier then stop player moving
  void checkCollide() {
   if (playerPosition.y <= barrierHeight + playerHeight && playerPosition.x <= barrierWidth + playerWidth)
   {
     println("COLLIDED");
     playerPosition.x = barrierPosition.x + 10;
   }

  }

void drawPlayer() {
  fill(255,0,0);
  rect(playerPosition.x,playerPosition.y,playerWidth,playerHeight);  
}
void drawBarrier() {
  fill(0);
  rect(barrierPosition.x,barrierPosition.y,barrierWidth,barrierHeight);  
}

void movePlayerPosition() {

    //moves up and down
    if (goUp && playerPosition.y > 0)
    {
      playerPosition.y = playerPosition.y - velocity;
    } else if (goDown && playerPosition.y < 598-playerHeight)
    {
      playerPosition.y = playerPosition.y + velocity;
    }

    //moves right and left
    if (goLeft && playerPosition.x > 0)
    {
      playerPosition.x = playerPosition.x -velocity;
    } else if (goRight && playerPosition.x <800-playerWidth)
    {
      playerPosition.x = playerPosition.x + velocity;
    }
  }

  //if the keys are pressed move in that direction
void keyPressed() {
  if (key == 'w') {
    goUp=true;
  } else if (key == 'a') {
    goLeft=true;
  } else if (key == 's') {
    goDown=true;
  } else if (key == 'd') {
    goRight=true;
  }
}
//if the keys are released stop moving
void keyReleased() {
  if (key == 'w') {
    goUp=false;
  } else if (key == 'a') {
    goLeft=false;
  } else if (key == 's') {
    goDown=false;
  } else if (key == 'd') {
    goRight=false;
  }
}

Answer 1

Simple answer first; Your checkForCollide method should return a boolean instead of been void, then you can use this method with your movePlayerPosition one and only perform the X axis movement when there has been no collision.

Now, in a more complete answer; You should study a little more about the subject, there are a lot of patterns and libraries to better and easier handle this topic. I recommend you the Nature of code, you can get this pdf for free and you have a lot about the use of physic libraries from chapter 5 and on, also lots of samples about programming games.

Hope this helps and good luck. Regards Jose