Java 2D collision response method

Question

Recently I have been playing around with basic 2D java game programming and have been having a lot of fun discovering things on my own, but I have come up with a problem. I have created a simple collision method that has been extremely buggy. So my question is how to change the x and y of the player when they collid with a block. I have tried the below code and it is recognizing when the player has collided but it doesn't set his x and y to the x and y to the tempx and y. Code:

private void update(){
    tempx = player.getX(); 
    tempy = player.getY();
    collided = checkCollision();
    if(collided == false){
        player.update();
    }
    else if(collided){
        player.setX((int)tempx);
        player.setY((int)tempy);
        System.out.println("COLLIDED");
    }
}

private boolean checkCollision(){
    for(int i = 0; i < tiles.size(); i++){
        Tile t = tiles.get(i);
        Rectangle tr = t.getBounds();
        if(tr.intersects(player.getBounds())){
            return tr.intersects(getBounds());
        }
    }
    return false;
}

The collision is being detected but the player x and y aren't being changed accordingly. If you need more code or have any questions just ask. Thanks for any help:)

P.S. I have tried adding gravity and the collision only works for the top of the blocks if that is any help

Below is the player.update() method:

@Override
public void keyPressed(KeyEvent e){
    int k = e.getKeyCode();
    if(k != 0){
        if(k == KeyEvent.VK_W){
            y -= vy;
        }
        else if(k == KeyEvent.VK_A){
            x -= vx;
        }
        else if(k == KeyEvent.VK_S){
            y += vy;
        }
        else if(k == KeyEvent.VK_D){
            x += vx;
        }
    }
}
public void update(){

}

Answer 1

The problem appears to be in your update method.

private void update(){
    tempx = player.getX(); // tempx now is the same as the players x location
    tempy = player.getY();
    collided = checkCollision();
    if(collided == false){
        player.update();
    }
    else if(collided){
        player.setX((int)tempx);  // you set players location equal to temp, which is 
        player.setY((int)tempy);  // already the players location
        System.out.println("COLLIDED");
    }
}

Since you are setting the players location equal to the location that it is currently in, you're not going to see the character move anywhere at all. You'll probably want to change the values of tempx and tempy

tempx = player.getX() + 10; 
tempy = player.getY() + 10;

Update

There seems to be some confusion about how the updating process is working.

Consider the following:

• character starts at (0,0)
• some object at (2,2) chich would cause a collision

Given the above the following happens in your update method and IN THIS ORDER

• tempx = player.getX() both x's are now 0
• tempy = player.getY() both y's are now 0
• checks collision, there are none
• since no collisions, player is updated. (I'll presume the update method moves the character (+1,+1). So character is now at location (1,1).
• tempx and tempy are set to getX and getY again. X and Y are now both 1. Now tempx and tempy are also 1
• no collisions, so character is updated (moved) to (2,2)
• tempx and tempy are set to getX and getY. X and Y are now both 2, so tempx and tempy are also 2.
• checks collisions, its true there was one at (2,2)
• because there was a collision you then "move" the character to tempx and tempy, BUT tempx and tempy are the same value as character.getX and character.getY.

You have to set tempx and tempy equal to the characters location outside of the update loop if you want them to remain the same throughout the characters updated movements.