structure for holding data in this instance (Hashmap/ArrayList etc)?

Best way to describe this is explain the situation.

Imagine I have a factory that produces chairs. Now the factory is split into 5 sections. A chair can be made fully in one area or over a number of areas. The makers of the chairs add attributes of the chair to a chair object. At the end of the day these objects are collected by my imaginary program and added into X datatype(ArrayList etc).

When a chair is added it must check if the chair already exists and if so not replace the existing chair but append this chairs attributes to it(Dont worry about this part, Ive got this covered)

So basically I want a structure than I can easily check if an object exists if not just straight up insert it, else perform the append. So I need开发者_如何学编程 to find the chair matching a certain unique ID. Kind of like a set. Except its not matching the same object, if a chair is made in three areas it will be three distinct objects - in real life they all reperesent the same object though - yet I only want one object that will hold the entire attribute contents of all the chairs.

Once its collected and performed the update on all areas of the factory it needs iterate over each object and add its contents to a DB. Again dont worrk about adding to the DB etc thats covered.

I just want to know what the best data structure in Java would be to match this spec.

Thank you in advance.

I'd say a HashMap: it lets you quickly check whether an object exists with a given unique ID, and retrieve that object if it does exist in the collection. Then it's simply a matter of performing your merge function to add attributes to the object that is already in the collection.

Unlike most other collections (ArrayList, e.g.), HashMaps are actually optimized for looking something up by a unique ID, and it will be just as fast at doing this regardless of how many objects you have in your collection.

This answer originally made reference to the Hashtable class, but after further research (and some good comments), I discovered that you're always better off using a HashMap. If you need synchronization, you can call Collections.synchronizedMap() on it. See here for more information.

I'd say use ArrayList. Override the hashcode/equals() method on your Chair object to use the unique ID. That way you can just use list.contains(chair) to check if it exists.

I'd say use an EnumMap. Define an enum of all possible part categories, so you can query the EnumMap for which part is missing

public enum Category {
    SEAT,REST,LEGS,CUSHION
}