从Hashmap返回信息

Question

Basically what I'm trying to do is store two values into a hashmap, i've tried a dictionary and failed with that as-well, anyhow, here we go.

private HashMap<Integer, Integer> dropTable = new HashMap<Integer, Integer>();

Then, in my code I have this

    for(int npc = 0; npc < 10; npc++){
        dropTable.put(npc, Constants.itemDrops[npc][1]);
    }

Basically, what I'm trying to do is save the values in this manner (With the ItemID being what is returned in the itemDrops array

<ArrayIndex, ItemID>

How,ever when I try to return this information, i can't figure it out.

Here is how I attempted returning this value

        for(int i = 0; i < dropTable.size(); i++) {
        System.out.println("NPC: " + dropTable.get((Integer)i));
    }

However, that returns null, and looking at it, it wont give me what I need.

How would I go about retrieving the Key/Value separately from the HashMap based on the Index of the HashMap? (If Hashmaps even have Index's, that's what I'm under the impression of)

=============== My idea of a hashmap.

<Integer>, <Integer> Index: 0
<Integer>, <Integer> Index: 1
etc...

Answer 1

HashMaps are unsorted, do not have indexes and the order features are returned during iteration is not guaranteed to be the order of insertion.

There are other Map objects available which provide some of these features. TreeMap is sorted for example.

All Maps provide a method keySet() which provides the set of Keys in an iterator and a similar values() Collection iterating over these objects is likely to provide the sort of behavour you wish.

Answer 2

First thing to aks, is a hashmap realy the data structure you need?

If not not then just use a simple List and use its get(index) method!

If Yes then you could use a Map implmentation - such as LinkedHashMap - that preserves the insert/put order. Then you can call values() of that map and iterate over it using enhanced for-loop, or probably also create a List and passing it the collection reurned if you need index access.

Answer 3

If you are looking to get a your objects according to an index - what you are really looking for is an ArrayList - which allows access by index, and is basically a dynamic array .

If you want to objects "attached" to the same index, you can use 2 ArrayLists (one for each type of object) - or use a Pair (from apache commons) as an element in the arraylist.