Counter.java

// (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
import greenfoot.Actor;
import greenfoot.Color;
import greenfoot.GreenfootImage;

/**
 * A Counter class that allows you to display a numerical value on screen.
 * 
 * The Counter is an actor, so you will need to create it, and then add it to
 * the world in Greenfoot. If you keep a reference to the Counter then you can
 * adjust its value. Here's an example of a world class that displays a counter
 * with the number of act cycles that have occurred:
 * 
 * <pre>
 * class CountingWorld {
 * 	private Counter actCounter;
 * 
 * 	public CountingWorld() {
 * 		super(600, 400, 1);
 * 		actCounter = new Counter("Act Cycles: ");
 * 		addObject(actCounter, 100, 100);
 * 	}
 * 
 * 	public void act() {
 * 		actCounter.setValue(actCounter.getValue() + 1);
 * 	}
 * }
 * </pre>
 * 
 * <br>
 * from the Greenfoot class library
 * 
 * @author Neil Brown and Michael Kölling
 * @version 1.0
 */
public class Counter extends Actor {
	private static final Color transparent = new Color(0, 0, 0, 0);
	private GreenfootImage background;
	private int value;
	private int target;
	private String prefix;

	public Counter() {
		this(new String());
	}

	/**
	 * Create a new counter, initialised to 0.
	 */
	public Counter(String prefix) {
		background = getImage(); // get image from class
		value = 0;
		target = 0;
		this.prefix = prefix;
		updateImage();
	}

	/**
	 * Animate the display to count up (or down) to the current target value.
	 */
	public void act() {
		if(value < target) {
			value++;
			updateImage();
		} else if(value > target) {
			value--;
			updateImage();
		}
	}

	/**
	 * Add a new score to the current counter value. This will animate the counter
	 * over consecutive frames until it reaches the new value.
	 */
	public void add(int score) {
		target += score;
	}

	/**
	 * Return the current counter value.
	 */
	public int getValue() {
		return target;
	}

	/**
	 * Set a new counter value. This will not animate the counter.
	 */
	public void setValue(int newValue) {
		target = newValue;
		value = newValue;
		updateImage();
	}

	/**
	 * Sets a text prefix that should be displayed before the counter value (e.g.
	 * "Score: ").
	 */
	public void setPrefix(String prefix) {
		this.prefix = prefix;
		updateImage();
	}

	/**
	 * Update the image on screen to show the current value.
	 */
	private void updateImage() {
		GreenfootImage image = new GreenfootImage(background);
		GreenfootImage text = new GreenfootImage(prefix + value, 22, Color.BLACK, transparent);

		if(text.getWidth() > image.getWidth() - 20) {
			image.scale(text.getWidth() + 20, image.getHeight());
		}

		image.drawImage(text, (image.getWidth() - text.getWidth()) / 2, (image.getHeight() - text.getHeight()) / 2);
		setImage(image);
	}
}