Thread: Adding value to existing map key

So I have a map:

Map<String, Integer> totals = new LinkedHashMap<String, Integer>();

I'm going to have about 6 running totals and I figured rather than creating 6 different variables, why not put it into a map. The only problem I have is, how do you add a value to an existing map entry? The map only seems to have the put method so I'm not sure how to go about this?

Any ideas? Am I over-complicating the situation?

Nevermind. I think I'm over-complicating it because now I have to check to see if the key exists or not... gah. Not worth it.

The map only seems to have the put method

Are you sure? I think it has many methods.

Well, it obviously has many methods, but it doesn't seem to have another method for adding a value to an existing key. I guess I could use put to add the existing value of that key to the new value but again, I have to check to see if the key exists yet or not and that's just a lot of extra processing.

method for adding a value to an existing key.

The key is associated with one value.
What do you mean by "adding a value" to a key?
You can change the value of the value object or you can replace the value object that is associated with the key.
Yes that will require some processing.

Well yeah, I understand how the map works. I guess what I want is:

mymap.add("key", value);

And that doesn't seem to exist. And I guess it makes sense that it wouldn't be there by default since maps can have any datatype as the value, so whatever. I went another route this time.

What would the add() method do?

Take the new value, add it to the existing value for the provided key.

Then you'd need a remove() method and a update() method and so on and on

What would be the result of add() when the current value is a String and the value to be added is a JComponent?

Well yeah, so maybe what I'm looking for is a map that is extended for this purpose.

You'd get a error if you tried to pass in a non-string... not sure what you're getting at?

Just talking about programming.

I do this for web stats - counting hits on an URL, visits from an IP address, visits from a country, counting the number of each HTTP response status code, that kind of thing. I use a HashMap for each 'kind' of count, and use an 'increment' method that as has arguments the HashMap and the key. The method retrieves the existing total and increments it, puts it back in, or creates a '1' entry if the key is new.

If you know in advance that you're only ever going to have 6 totals, it seems a waste of time: just create 6 variables.

Yeah. Not worth it for this instance. If it would be something different, it might be worth exploring.