Collision Detection

// For the Door class code
 // add the following to your instance variables
// this will allow for opening AND closing the door
private boolean opened = false;
// change the checkKeyPress method to the following
public void checkKeyPress()
{
    if (Greenfoot.mouseClicked(this))
    {
        Greenfoot.playSound("door-open-7.wav");
        // the next statement will allow the sound to process some
        // before the action of the door is seen
        Greenfoot.delay(20);
        // here we change the state of the door
        opened = !opened
        // and now set the appropriate image
        if (!opened) setImage(image1);
        else setImage(image2);
    }
}

// for the Radio class
// the complete class code follows
import greenfoot.*; 

public class Radio extends Actor
{
    // we save the GreenfootSound object in an instance variable (aka: object field)
    GreenfootSound gs = new GreenfootSound("Animal Crossing - K.K. Aria.mp3");

    public void act()
    {
        if (Greenfoot.mouseClicked(this))
        {
            if (!gs.isPlaying()) gs.play();
            else gs.stop();
        }
    }
}