Player Inventory

Newbie & Debugging Questions
#1

Hello~!

I’m new to Game Programming using Java, and I’m sort of kind of just playing around with various tutorials to grasp the concepts of using Java to create Games.
There is one thing I’m having a little trouble with, and I was hoping someone could shed some light for me.

[b]First[b]
Are there any tutorials specifically to learn how to create RPG games using Java?
I’ve tried to use Google, but of the 1928390182630916208 billion websites on game programming, only about 200 are written in Java, and of those 200, only about 3 are specific to RPG games >.< (common sense, and yes, im exaggerating)

Disclaimer: Yes, I do realize Java is already not the best option for creating games, let alone RPGs. I simply enjoy the challenge; and yes, I do have knowledge of the Java (and many other) language(s).

[b]Second[b]
I realize that’s a TON of code (well, at least a good chunk), so I won’t ask anyone to “code for me”, but can someone perhaps give me a detailed, step by step explanation on how I should go about creating an inventory class that is easy and effective?

I suppose I could create an inventory method:
inventory( ADD, “Herb”, 1); //add or delete, name, quantity

To add the item, I would create an object of class Item:
Item item = new Item( “Herb”, “Description of Herb”, 50, 200, 0 ); //name, description, buy value, baseValue, type

How would I go about deleting that?
Item item = new Item( “”, “”, 0, 0, 0 ); <== override object item?
^ that wouldn’t delete it though right? If I were to view the player’s inventory, I think I’d just see a blank line. rawr

#2

Welcome to Java game programming.
Java2D is fine for games if your not expecting to do a lot of alpha effects or particles. Otherwise I suggest using a library that supports such things.

This tut should help you:http://fivedots.coe.psu.ac.th/~ad/jg/

For items in my game I have a list of Item objects in the player class, so removing a item would just simply remove that item from the list.

HashTable<Item,String> items = new HashTable< Item, String >();

So you could make a method like:

void RemoveItemByID(String ID){
items.remove(ID);

}
#3

Hi!

It is only your opinion based on prejudices. Some people here (at least me) think that Java is the best fitted language for cross-platform game programming.

Look at JCRPG, it is really impressive:

#4

I think the entry types are swapped here!?

If you need to have multiple items under a specific name/id (like in some RPG inventories), you could just store a List in the HashMap:


public class Inventory
{
  HashMap<String,ArrayList<Item>> items = new HashMap<String,ArrayList<Item>>();

  public void add(Item item)
  {
     String name = item.getName();
     ArrayList<Item> itemGroup = items.get(name);
     if(itemGroup==null) // add a new group, if none exist, yet
     {
       itemGroup = new ArrayList<Items>();
       items.put(name,itemGroup);
     }
     itemGroup.add(item);
  }

  public void remove(String name){
     String name = item.getName();
     ArrayList<Item> itemGroup = items.get(name);
     if(itemGroup==null) return;
     itemGroup.remove(name);
     // remove an empty group
     if(itemGroup.size()) == 0;
     items.remove(name);
  }
#5

Woops yes your right there swapped, my browser is missing an inbuilt Java IDE ::slight_smile:
I have the quantity value in the Item object itself which removes the need for that ArrayList, unless there’s another reason to have the same ID?

#6

Nope. It’s just that if you have a stack of herbs or something you usually only remove one item from this stack, if you use it. Your removeByID would remove the whole stack.

#7

Oh yes in my removeByID method would remove them all, I wasn’t thinking about quantities when I posted that.
So yes that would need to be modified.

#8

Wow, thank you all so much for the tips and linkies~!
I wasn’t expecting so much help so quickly, much appreciated

BTW

Thanks for the warm welcome~! Have a /cupcake :smiley:

I’m actually familiar with this website (and have purchased the book, void of CD, so I have to refer to this site continuously, considering the author doesn’t have a single page in the book that “reviews” the code for that chapter - goodness me)

The website is currently experiencing a page load error (perhaps they’re simply doing maintenance) so if any curious readers hop into this thread and click the link - it isn’t broken.

tyvm 4 all ur help!

I concur with you, I’ve also previously seen JCRPG (and I’ve been told Runescape was created in Java by a 15 year old boy). The only problem is, of the 8709816-238162-93861-9236-1` million websites devoted to game programming, only ~200 are written in java, and only 3 are RPGs (previously exaggerated example).
So, yes, I suppose my opinion is based on prejudices and Chapter 1 of Killer Game Programming in Java. :\

I do think Java has AMAZING capabilities (that’s for sure) - after all my online bank allows me to scan my paycheck straight into my checking account (that’s pretty awesomesauce imo)
And I would LOVE to learn more about the language and how I can apply it to creating games (regardless if i currently think I could create a game much easier in C++ or visual basic, or the XNA studio, or any of the microsoft visual studio programs… but probably best to stick with C++)

Also Many Thanks to
cylab & zammbi for collaborating on the best way for me to go about creating an inventory. many /cupcakes to you two~!

#9

Hmm, worked a couple of minutes before - maybe you broke it :wink: Ahh, works again…

You are welcome. Usually java-gaming.org is an extremly friendly and helpfull community.

Btw. interesting video blog :wink:

#10

HAHAHAHAHAHHAHA yea, im a little cooky :stuck_out_tongue:
I should really take that off there >.< but it still makes people laugh, so I suppose it’s going to stay up :smiley:

#11

Yeah I’d agree with everyone here that you should be treating your inventory more as a list than as an array. In your original idea over how to do it, you seemed to have been treating it this way by needing to fill in blank spaces when an item was taken away. Instead, just use a list and then print it out however you want in your inventory menu. If you think of it that way then you don’t really need to worry about any of the outliers - it’s just list access, which is easy.

You could use a HashMap also like zammbi recommended, but I don’t necessarily see a reason for this because typically item access will be chosen by the user and therefore can be index-based. If you have a lot of event-stuff happening based on items (like if(playerHasItem(“Doggy”) { foo(); } ) then it’s logical to use a HashMap so you can get that O(1) access. But any time a player is selecting an item, using one from an inventory screen, or even if all the items are being drawn out in the inventory, then a HashMap will be slower and more convoluted to use in terms of accessing elements.

In the end I think it really depends upon the uses you’re going to need to get out of it.

#12

I think one should use a HashMap just because of it’s simplicity. Speed won’t likely be an issue with an inventory…

#13

I am making an rpg aswell. This is gunn abe helpful when/if I make an inventory.

#14

hi, you may want to check this out
http://roguebasin.roguelikedevelopment.org/index.php?title=Main_Page

rouges arnt necessarily intense rpgs, but are and can be mini-rpgs and can also be dungeon crawlers.

The wiki goes through how random maps and maps can be created, also here is another article for your read,

http://www-cs-students.stanford.edu/~amitp/gameprog.html#tiles
i find this website very interesting :slight_smile:

#15

If you treat the inventory as a list you’ll lose position information. If you imagine your inventory on screen as a grid of boxes then if you treat it as a list, when you remove an item all the other items will slide through the grid to close the now empty space.

There’s nothing wrong with using an array for inventory. Something like:


public class Inventory {
     private static final int MAX_INVENTORY_SIZE = 100;

     private Item[] items = new Item[MAX_INVENTORY_SIZE];

     public Inventory() {
     }

     public boolean addItem(Item item) {
           int slot = findFreeSlot();
           if (slot >= 0) {
               items[slot] = item;
           }
     }

     public Item removeItem(Item item) {
           for (int i=0;i<items.length;i++) {
                if (items[i].equals(item)) {
                      Item temp = items[i];
                      items[i] = null;
                      return temp;
                }
            }

            return null;
     }

     public Item getItemAt(int index) {
            return items[index];
     }

     public int getInventorySize() {
             return MAX_INVENTORY_SIZE;
     }

     private int findFreeSlot() {
          for (int i=0;i<items.length;i++) {
               if (items[i] == null) {
                    return i;
               }
          }

          return -1;
     }
}

works fine (just typed, not compiled). The interesting bits come when you want to start stacking quantities of items on top of each other. On the other hand, if you’re not expecting the normal behavior from your inventory when you display it then lists might work just fine for you. Best idea would be to wrap it up in an Inventory class and then decide when you have a reason to what needs to be done internally.

Kev

#16

Yeah, that’s true, Kev. I actually prefer to have the empty spaces fill in. Basically the list is compacted to be as minimally sized as possible. Then you can order it however you want as a player. It sorta depends what you want. If you’re going for something like Legend of Zelda where everything has a set slot, then position information is very important. Also if it’s like World of Warcraft where you have bag slots, then position also matters. If you are doing something more like Final Fantasy, however, then a list probably makes more sense.

Either way there probably is no best way to do it, and cylab was right when he said speed isn’t really important in an inventory. So function is what you should design for.

#17

You have been misinformed. RuneScape started out as a university project, so Andrew was probably 20 when he started. He may have written parts of his graphics and audio libraries when he was 15.

As far as tutorials, there are plenty of general tutorials covering things like the collections framework, 3D rendering, etc. Read and understand those. If you do find an RPG tutorial but you don’t understand the basics then you’ll end up with a lot of code you can’t debug. If you understand the basics, including basic OO design, you won’t have much need for an RPG tutorial (or, at least, not for a language-specific one).