I am stuck with a downcasting issue with java.
Here is the plot:
The class MyPicture extends the abstract class BufferedImage. The point is to add a few methods to BufferedImage. Then, I have the class MyWindow which sets a user-friendly window. In this class, I want to load a picture in MyPic, copy it in MyPic_filtered, use a method used in MyPicture on MyPic_filtered and finally show MyPic and MyPic_filtered in separated windows (but this last part is OK ^^).
I don't know which types I should use for MyPic and MyPic_filtered. I tried the cast them in the right type, it builds but doesn't run.
Here is the code:
//Loading the picture
BufferedImage MyPic = ImageIO.read(new File(URL)); //URL is a string
//Copy the picture
MyPicture myPic_filtered = myPic;
//Use the method from MyPicture
myPic_filtered.method_from_MyPicture();`
Could someone help me please?
You can add a caster when you are trying to pass a base class instance to extended one, like:
MyPicture myPic_filtered = (MyPicture)myPic;
Then you can access "myPic" by using this keyword.
Or maybe you do not need to extend the BufferedImage. Just treat bufferedImage as an instance variable, like:
class MyPicture {
BufferedImage bi;
//other variables
......;
public MyPicture(BufferedImage input) {
this.bi = input;
}
public BufferedImage method_from_MyPicture() {
//Do something with bi and output
........
}
}
Not sure which structure is better. But it solves the problem in either way.
The code below shows my Assets class which allows me to load the texture once and call it when I need it globally. If you see that my pack is called house1.pack meaning that there will be more than one house with different art styles. I was wondering if I could achieve a design similar to the popular app Clash Royale with my current code and minor tweaks. I want there to load a different .pack file based on player rank when they are in game. The different houses have the same objects with the same png file names and sizes, but they are just drawn differently.
Thanks,
Denfeet
public class Assets implements Disposable, AssetErrorListener {
public static final String TAG = Assets.class.getName();
public static final Assets instance = new Assets();
private AssetManager assetManager;
public AssetFonts fonts;
public AssetDoor door;
public AssetPlatform platform;
public AssetPlayer player;
public AssetControls controls;
// singleton
private Assets() {
}
public void init(AssetManager assetManager) {
this.assetManager = assetManager;
assetManager.setErrorListener(this);
assetManager.load("TexturePacker/house1.pack", TextureAtlas.class);
assetManager.finishLoading();
TextureAtlas atlas = assetManager.get("TexturePacker/house1.pack");
//create game resource objects
fonts = new AssetFonts();
door = new AssetDoor(atlas);
platform = new AssetPlatform(atlas);
player = new AssetPlayer(atlas);
controls = new AssetControls(atlas);
}
#Override
public void error(AssetDescriptor asset, Throwable throwable) {
Gdx.app.error(TAG, "Couldn't load asset '" + asset.fileName + "'", (Exception) throwable);
}
public class AssetFonts {
...
}
public class AssetPlayer {
...
}
public class AssetControls {
...
}
public class AssetDoor {
...
}
public class AssetPlatform {
...
}
}
You can load and unload assets at any time. Provided you don't want to use house1.pack anywhere else in your game, you can:
assetManager.unload("TexturePacker/house1.pack")
to dispose of your house1.pack, then do most of what you have in your init() method to again
assetManager.load("TexturePacker/house2.pack", TextureAtlas.class);
assetManager.finishLoading();
//etc
Not sure how you'd structure your code, but the above is the idea. Depending on how many assets you're talking about (loading time), you may need a natural transition point (not necessarily a full loading screen). But if you want to change textures from one house to another on the fly, you'd probably want to load them all at once at the beginning and find a different method to swap them.
The Picasso library allows one to load an image easily like:
Picasso.with(context).load(url).into(imageview);
The API also allows to specify an error image. But what can I do if I want the library to first try three or four different URLs before giving up and displaying the error image? Ideally these images would be tried sequentially, falling back to the next one if the previous wasn't loaded.
Natively there's no API for such functionality. But with some clever coded Picasso.Target you can easily achieve such functionality.
I'll add here a quick hack-untested code that should give you a rought idea on what to look for. You'll have to test and maybe fine tune, but that should be pretty OK.
private static final List<MultiFallBackTarget> TARGETS = new ArrayList<MultiFallBackTarget>();
public static class MultiFallBackTarget implements Picasso.Target {
private WeakReference<ImageView> weakImage;
private List<String> fallbacks;
public MultiFallBackTarget(ImageView image){
weakImage = new WeakReference<>(image);
fallbacks = new ArrayList<String>();
TARGETS.add(this);
}
public void addFallback(String fallbackUrl){
fallbacks.add(fallbackUrl);
}
public void onBitmapLoaded(Bitmap bitmap, LoadedFrom from){
removeSelf();
ImageView image = weakImage.get();
if(image == null) return;
image.setImageBitmap(bitmap);
}
public void onBitmapFailed(Drawable errorDrawable){
ImageView image = weakImage.get();
if(image == null) {
removeSelf();
return;
}
if(fallbacks.size() > 0){
String nextUrl = fallbacks.remove(0);
// here you call picasso again
Picasso.with(image.getContext()).load(nextUrl).into(this);
} else {
removeSelf();
}
}
public void onPrepareLoad(Drawable placeHolderDrawable){}
private void removeSelf(){
TARGETS.remove(this);
}
}
Remember that Picasso does not hold strong references to the Target you put inside into(object). That means, internally Picasso uses WeakReference to that.
So that means that you need that self reference in TARGETS to keep reference of all MultiFallBackTarget you create and allow them to self-remove when their job is done.
Overview
In my (Android) Java game, I have a class called resources. As the name suggests, this class holds the resources for the game. All of my OpenGL objects (Sprites) are created here
It's looks something like the following (obviously, this is a simplified version compared to that which appears in the real project):
public class Resources {
Hero hero;
Enemy enemy;
MenuButtons mainMenuButtons;
Background background;
Scene mainMenu;
public void createObjects(){
hero = new Hero();
enemy = new Enemy();
mainMenuButtons = new MenuButtons();
background = new Background();
mainMenu = new Scene(this);
}
}
So, within my mainMenu scene, I need access my objects, so we may see something like this:
public class mainMenu implements Scene {
Resources resources;
public mainMenu(Resources resources){
this.resources = resources;
}
#Override
public void render(){
resources.background.draw();
resources.hero.draw();
resources.enemy.draw();
mainMenuButtons.draw();
}
#Override
public void updateLogic(){
resources.hero.move();
resources.enemy.move();
resources.mainMenubuttons.animate();
}
}
Now, the above method is just one way to get access to the objects in resources and their methods. But does this actually break the Law of Demeter? If not, why not? If so, what is the best way to get access to these objects in a way that does not violate the LOD?
Accessors?
One option (which I've ruled out TBH - see below) is placing accessor methods into my resources class. So that I could do something like:
resources.drawBackround();
I have a lot of objects and I need an accessor for each method/variable of each object. Not really practical, it seems like I'm writing a ton of extra code and most importantly, it makes the resources class ridiculously long as it becomes filled with these accessors. Therefore, I'm not going down this road.
Passing in objects into the scene's constructor
Of course, I can also do something like this:
hero = new Hero();
enemy = new Enemy();
mainMenuButtons = new MenuButtons();
background = new Background();
mainMenu = new Scene(hero, enemy, mainMenuButtons, background);
So I can simply do this:
background.draw(); //etc....
This is workable for simple scene's (such as menu systems that don't require a lot of objects) but for the main game, it could quickly become a mess as I'd have to pass references to some 30+ objects into the constructor which doesn't really sound quite right......
So I would really appreciate if someone could point out the best way to proceed and why.
So I would really appreciate if someone could point out the best way to proceed and why.
The best way, in my opinion, is to keep the Resources class, make all objects private to not break the law and write accessors (but not for every object like you already ruled out).
I have a lot of objects and I need an accessor for each method/variable of each object. Not really practical, it seems like I'm writing a ton of extra code and most importantly, it makes the resources class ridiculously long as it becomes filled with these accessors. Therefore, I'm not going down this road.
I assume many objects are of the same class. So you do not have to make an accessor for every object what would really blow up the class.
I a game you normally have a hero, one or more enemies and many sprites.
public class Resources {
private Hero hero;
private Enemy enemy;
private MenuButtons mainMenuButtons;
private Background background;
private Scene mainMenu;
public void createObjects(){
hero = new Hero();
enemy = new Enemy();
mainMenuButtons = new MenuButtons();
background = new Background();
mainMenu = new Scene(this);
}
public Hero getBackground() {
return background;
}
public Hero getHero() {
return hero;
}
public List<Enemy> getEnemies() {
ArrayList<Enemy> list = new ArrayList<Enemy>();
list.add(enemy);
list.add(next_enemy);
return list;
}
public List<Sprite> getSprites() {
ArrayList<Sprite> list = new ArrayList<Sprite>();
list.addAll(enemy.getActiveSprites());
return list;
}
}
Instead of getHero() and getEnemy() you could also make a getActor() method if Hero and Enemy are derived from the same class.
The getSprites() method is just an example how it could look like.
If that solution is not going to work for you, I have another suggestion.
Make the Resources class do some work.
public class ResourceManager {
private Hero hero;
private Enemy enemy;
private MenuButtons mainMenuButtons;
private Background background;
private Scene mainMenu;
public void createObjects(){
hero = new Hero();
enemy = new Enemy();
mainMenuButtons = new MenuButtons();
background = new Background();
mainMenu = new Scene(this);
}
public void render(Scene scene) {
this.background.draw();
if (scene != mainMenu) {
this.hero.draw();
this.enemy.draw();
}
this.mainMenuButtons.draw();
}
public void updateLogic(Scene scene){
this.hero.move();
this.enemy.move();
this.mainMenubuttons.animate();
}
}
The mainMenu then calls logic methods directly in the RescourceManager class.
public class mainMenu implements Scene {
ResourceManager resourceManager;
public mainMenu(ResourceManager resourceManager){
this.resourceManager = resourceManager;
}
#Override
public void render(){
resourceManager.render(this);
}
#Override
public void updateLogic(){
resourceManager.updateLogic(this);
}
}
I hope my suggestions helped you a bit figure out how to continue with your project.
You could use dependency injection and eliminate your Resources class. Then you can call functions on your fields and wouldn't be in violation of the Law of Demeter.
Here is an example using constructor injection:
public class MainMenu implements Scene {
Background background;
Hero hero;
Enemy enemy;
MenuButtons buttons
public mainMenu(Background background, Hero hero, Enemy enemy, MenuButtons buttons){
this.background = background;
this.hero = hero;
this.enemy = enemy;
this.buttons = buttons;
}
#Override
public void render(){
this.background.draw();
this.hero.draw();
this.enemy.draw();
this.mainMenuButtons.draw();
}
#Override
public void updateLogic(){
this.hero.move();
this.enemy.move();
this.mainMenubuttons.animate();
}
}
With dependency injection, you pass instances into constructors and functions instead of "newing" them inside your class. You need to manage your instances somewhere though, and there are plenty of libraries that will do that for you. Dagger is a popular one for Android: http://square.github.io/dagger/
The idea of passing a list isn't a bad first step, but it's not sufficient. Game developers have a (somewhat controversial) concept of a structure called a "scene graph" that helps them keep track of their resources (among other things). https://en.wikipedia.org/?title=Scene_graph
It's a pretty complicated concept, but you're going to need to learn about it sooner or later. There's a lot of good advice on gamedev.stackexchange.com, so I'd suggest you take a peek over there.
Here's a nice YouTube video tutorial on the subject. https://www.youtube.com/watch?v=ktz9AlMSEoA
You could create an Drawer class that handles the drawing of all the objects. Your scene objects simply need to feed the Drawer the objects that I assume are Drawable.
public class Drawer {
public void drawObjects(Drawable... objects) {
for(Drawable drawable : objects) {
drawable.draw();
}
}
}
This is then used by Scene to draw those objects.
public class mainMenu implements Scene {
Resources resources;
Drawer drawer;
...
public void render() {
drawer.drawObjects(resources.background,
resources.hero,
resources.enemy,
resources.mainMenuButtons);
}
...
}
A similar strategy, using an Updater, can applied for the other methods. If your updateLogic() method makes as simple of calls as it looks, you can definitely do the same thing, by making all those objects inherit from an Updateable interface.
public interface Updateable {
void update();
}
Hero's and Enemy's update() methods could simply call their move() methods, while MenuButtons's update() could delegate to animate(), etc.
Obviously, if you like, you can use some sort of collection instead of varargs for the parameter of Drawer's drawObjects(). I just like the nice fluency made possible by the varargs, since you don't have to create the collection.
For other tips for keeping code in line with the Law of Demeter, check out this article: Law of Demeter and How to Work With It
I like the concept of a ResourceManager. But a ResourceManager should be responsilbe for loading Resources, caching and freeing them. Rendering is definitly a Method of a Render Object.
So the Scence - render Method could delegate the rendering to it after instantiating a Renderer and feed it with Drawables as the Renderer does not render Resources but renderable objects.
Say:
class MainMenu implements Scene {
Renderer sceneRenderer = new Renderer();
AnimatedRenderer animatedRenderer = new AnimatedRenderer();
ResourceManager resourceManager = ResourceManager.getInstance();
List<Resource> resources;
List<Drawable> renderedObjects;
GameObjectController gameObjectController;
void initializeScene() {
resources = resourceManager.getResources();
renderedObjects = resourcesAsRenderables();
sceneRenderer.setDrawables(renderedObjects);
}
List<Drawable> resourcesAsRenderables() {
// if resources are not directly renderable, do decoration etc
// and return a List of Drawable
}
#Override
public void render(){
sceneRenderer.render();
}
#Override
public void updateLogic(){
moveGameObjects();
doAnimations();
}
protected void moveGameObjects() {
gameObjectController.moveAllObjects(this, resources);
}
protected void doAnimations() {
animatedRenderer.render(resources);
}
class ResourceManager {
private static ResourceManager instance = null;
List<Resource> resources;
public ResourceManager getInstance() {
if(instance == null) {
instance = new ResourceManager();
instance.loadResources();
}
return instance;
}
private void loadResources() {
resources = new LinkedList<Resource>();
resources.add(new Hero());
....
}
public List<Resource> getResources() {
return resources;
}
}
This clearly separates the logic and responsibilities for the tasks carried out during the scene lifecycle. A resource manager which is responsible for retrieving resources and as they may take long loading times does things like caching or freeing in low memory situations hiding the details from the client. A renderer which is responsible for displaying the objects and a controller which is responsible for moving the objects. The controller itself may implement handlers for keyboard events but that is not something which must be transparent to the scene. The renderer may swap backgrounds in or out or scale or set lighting effects but the scene only calls its render method. The animated renderer is responsible for starting , rendering and stopping animations.
Change this:
public void render(){
resources.background.draw();
resources.hero.draw();
resources.enemy.draw();
mainMenuButtons.draw();
}
#Override
public void updateLogic(){
resources.hero.move();
resources.enemy.move();
resources.mainMenubuttons.animate();
}
With this:
public void render(){
resources.render();
}
#Override
public void updateLogic(){
resources.update();
}
ResourceManager don't have to know what's inside Resources. It may be one enemy or ten, it doesn't care to ResourceManager.
And so in 'Resource' you can do:
public void update(){
hero.update();// Cause hero may, or may not move, he makes the choice
enemy.update();//...
mainMenubuttons.update();//.
}
public void render(){
...
}
More than this! you could change the "Resource" implementation with an interface and you will be programming for interfaces and not for implementations, which is cool! This way you can have a 'Resources' for in-game and another one for menus that will be used in same way: Only changing, at runtime, the concrete Resources you will be in a menu or in game!
Anyway, not always is needed to fill Demeter.
As can be seen your Resources dont need to be recreated, instead they do use some resources that cant be reloaded (probably images).
You should share the images object within a Resource class, and create your objects within a Scene class, on the constructor of the entities you can get the shared resource that is pre-loaded.
I have a List<Presenter> presenterList;
With
public class Presenter(){
String name;
String imageRef; // Filename to be downloaded
Bitmap image;
(etc...)
}
I'm working with AsyncTask & once the image has downloaded, I wish to go through the list and set Image value to the newly download image.
so far i have
Presenter pres = PresenterList.get(Position);
pres.Image = new (Bitmap) downloadedImageFromImageRef;
however i fear that this will not relate to the Image value of the presenter within the list.
How do i refer, or even assign to the specific Presenter attribute within the list?
From working with C (many years ago), i belive somthing like a pointer to the value in which to assign .Image would work
Thank you in advace
Well, if you have C experience, then the thing to know about Java is that it doesn't use pointers, but it does use references. So if I'm understanding your problem correctly, you are already using the Image attribute of a Presenter instance elsewhere and then you want to fill it in later. Assigning pres.Image = new (Bitmap) DownloadedImageFromImageRef; would not work in this case because other objects are looking at a different Bitmap object reference.
What you might need to do is use an observer pattern -- it depends on the details of your problem. Here's an example:
Somewhere in the code I have a class Foo that wants to use the Image property from a Presenter instance. But, since that property isn't set until later, this class wants to be notified when it is ready (it is an observer).
public class Presenter {
String Name;
String ImageRef; // Filename to be downloaded
private Bitmap Image;
private PresenterImageObserver observer;
public void setImageObeserver(PresenterImageObserver pio) {
this.observer = pio;
}
public void setImage(Bitmap b) {
this.Image = b;
this.observer.imageLoaded(b);
}
}
public interface PresenterImageObserver {
public void imageLoaded(Bitmap b);
}
public class Foo implements PresenterImageObserver {
//Foo's constructor. It wants the image from presenter p, when it is ready
public Foo(Presenter p) {
p.setImageObserver(this);
}
public void imageLoaded(Bitmap b) {
//b contains the loaded image and this Foo instance can use it now!
}
}
You'd need to set the image using pres.setImage(new (Bitmap) downloadedImageFromImageRef);.
So you have to find in your list the Presenter for which the correct imageref. You have basically two options.
First, you simply iterate through your list
for (Presenter presenter: presenterList) {
if (presenter.imageref.equals(imageName) {
Presenter.image = new Bitmap(downloadedImage);
break; // found : stop iterations
}
}
Secondly, you can create a HashMap for your presenters, with the imageref as the key :
HashMap<String, Presenter> map = new HashMap<>();
for (Presenter presenter: presenterList) {
map.put(presenter.imageref, presenter);
}
Then, you can directly find the right presenter through map.get(imageName)