Java: Using an enum as an array reference

You can do almost it. In contrast to C++ where enum is just an int, Java's enum is class. So you can't use it as an index of array. But every enum element has ordinal() that is int, so you can say

amount[COAL.ordinal()]
price[IRON.ordinal()]

But you have a better approach. Can add methods to enum, so it will look like:

IRON.price(amounts)
COAL.amount(prices)

I think this approach is much better.

I think you're looking for EnumMap, http://docs.oracle.com/javase/1.5.0/docs/api/java/util/EnumMap.html

It's not exactly an array, but because the key is an enum, it's still space efficient.

It ends up like:

amount.get(Resource.COAL)

Each Java enum element has an ordinal associated with it, indexed from zero based on the order of definition in the enum. Just use e.g.

COAL.ordinal()

However, it sounds to me like you'd be better off creating a class e.g. Order with fields for Amount and Price and then keeping a collection of those e.g. in a Map indexed by the enum elements.

e.g.

Map<Resource, Order> orders = new HashMap<Resource, Order>();
orders.put(Resource.COAL, new Order(price, amount));

Maps are very good for more dynamic data. But you also have to code all the checking for double names, double values, existing names/values and all the stuff. And even in this case if you do the error, it will be found at runtime only.

For more static data better use not primitive enums, but new type enums from Java 6. They are excellent! And errors will be found by compiler.

public enum Resource{
    COAL(0), IRON(1);
    int index;
    private Resource(int index){
        this.index=index;
    }
}
...
amount[Resource.COAL.index]=...

But better variant is:

public enum Resource{
    COAL(538,0.5f), IRON(115,1.5f);
    int amount;
    float price;
    private Resource(int amount, float price ){
        this.amount=amount;
        this.price=price;
    }
}
...
Resource.COAL.amount=...

You can use their name.

You could make the cycle through all enum:

for(Resource resourceType: Resource.values()) { 
   String toOutput=resourceType.name()+" amount="+ resourceType.amount;
}

Unfortunately, you'll need a slightly longer syntax:

Amount[COAL.ordinal()] // The amount of coal
Price[IRON.ordinal()]  // The price of iron

If that is not to your liking, constants may be your only option, i.e.

public class Resource {
    public static final int COAL = 0;
    public static final int IRON = 1;

}

Hope that helps.