Animation.java

import java.awt.Image;
import java.util.ArrayList;


/**
    The Animation class manages a series of images (frames) and
    the amount of time to display each frame.
*/
public class Animation {

    private GamePanel panel;					// JPanel on which animation is being displayed
    private ArrayList<AnimFrame> frames;			// collection of frames for animation
    private int currFrameIndex;					// current frame being displayed
    private long animTime;					// time that the animation has run for already
    private long startTime;					// start time of the animation or time since last update
    private long totalDuration;					// total duration of the animation

    private boolean loop;
    private boolean isActive;

    /**
        Creates a new, empty Animation.
    */
    public Animation(boolean loop) {
        frames = new ArrayList<AnimFrame>();
        totalDuration = 0;
	this.loop = loop;
	isActive = false;
    }


    /**
        Adds an image to the animation with the specified
        duration (time to display the image).
    */
    public synchronized void addFrame(Image image, long duration)
    {
        totalDuration += duration;
        frames.add(new AnimFrame(image, totalDuration));
    }


    /**
        Starts this animation over from the beginning.
    */
    public synchronized void start() {
	isActive = true;
        animTime = 0;						// reset time animation has run for to zero
        currFrameIndex = 0;					// reset current frame to first frame
	startTime = System.currentTimeMillis();			// reset start time to current time
    }


    /**
        Terminates this animation.
    */
    public synchronized void stop() {
	isActive = false;
    }


    /**
        Updates this animation's current image (frame), if
        neccesary.
    */
    public synchronized void update() {

	if (!isActive)
	    return;

        long currTime = System.currentTimeMillis();		// find the current time
	long elapsedTime = currTime - startTime;		// find how much time has elapsed since last update
	startTime = currTime;					// set start time to current time

        if (frames.size() > 1) {
            animTime += elapsedTime;				// add elapsed time to amount of time animation has run for
            if (animTime >= totalDuration) {			// if the time animation has run for > total duration
		if (loop) {
                    animTime = animTime % totalDuration;	// reset time animation has run for
                    currFrameIndex = 0;				// reset current frame to first frame
		}
		else { 
	            isActive = false;				// set to false to terminate animation
		}
            }

	    if (!isActive)
	       return;

            while (animTime > getFrame(currFrameIndex).endTime) {
                currFrameIndex++;				// set frame corresponding to time animation has run for
            }
        }
	
    }


    /**
        Gets this Animation's current image. Returns null if this
        animation has no images.
    */
    public synchronized Image getImage() {
        if (frames.size() == 0) {
            return null;
        }
        else {
            return getFrame(currFrameIndex).image;
        }
    }


    public int getNumFrames() {					// find out how many frames in animation
	return frames.size();
    }


    private AnimFrame getFrame(int i) {				// returns ith frame in the collection
        return frames.get(i);
    }


    public boolean isStillActive () {
	return isActive;
    }


    private class AnimFrame {					// inner class for the frames of the animation

        Image image;
        long endTime;

        public AnimFrame(Image image, long endTime) {
            this.image = image;
            this.endTime = endTime;
        }
    }

}