Road to Coding HashMap

For the 0.2 Release for the processing.js project, I decided I should code some more supportive classes to expand the processing.js library. I picked HashMap, because this class is missing and I still remember coding a C++ HashTable for an assignment in my previous course DSA555.

I start by reading the specifications in the processing.js references, the original processing implementation, and the Java API, to get a sense of what HashMap is supposed to do. The general idea of HashMap is very similar to HashTable, but I want to know the exact differences between them. So I did a search on Google and found this website. HashMap is actually just a new version of HashTable that accepts null keys; plus a name change. I guess I can start coding it.

Of course, I will not waste my time to come up with original codes if there's is a HashMap existed in the web. Therefore, I did a search on Google again to search for HashMap implementation on Javascript. I found this, and it's great, because the first thing I see is a Map implementation. That means I can probably take the code and do little work to use it. But it turns out that the Map class is more complicated than I thought, plus where is the missing Hash part?

I continue scrolling down and see HashMap implementation. As soon as I start tracing the codes, I realize there's no Hash anywhere in the code. Isn't it weird? Then one Javascript feature on array reappears to me: I don't even need to set a size for array in Javascript!! That means there's no need to hash the given key and insert into a limited size HashMap!! So why do I even need to write a HashMap for the processing.js library? The built-in Javascript array can do the exact same job already. That means all the above researches is wasted?

I decide that I shall code a HashMap anyways, since it is a class listed under processing.js reference. So I continue to trace the HashMap implementation. I don't really have a full understand on the usage for a few lines of codes. So I guess I can just modify some codes so that I understand the code better and see if it works the same way before I change those lines. Original version vs. Modified version.

It did, so the next will be inserting this chunk of code into processing.js. To do this, I decide to look at ArrayList, which has already been coded by someone else. Amazingly, I see uses of the keyword this, and I got freaked out since Dave have said something about it being different than what Java's keyword this. Then Dave sent me a link to show me how to use the troublesome keyword.

So, I coded this HashMap and pushed into the GitHub repository. I know it is not good codes, but I tried my best. It doesn't have codes to copy from another implementation of Map, either. But with the tests I throw to the code, it does what it is expected. I will refine the code so that it does more HashMap functions.