Java Map between pairs and values

Question

I need to create a map which will cache results of a third party lookup service. The request is made up of two objects for example, time and month. The map needs to map between (time, month) and a result.

My initial idea is to make an object to wrap time and month into effectively a tuple object, so the cache is a map between this object and the result.

Is there a better way of doing this, without needing to wrap the request into the tuple object each time we need to use the cache?

Many thanks.

Answer 1

My initial idea is to make an object to wrap time and month into effectively a tuple object

That's the right idea. Override hashCode() and equals(Object) of your tuple to make it work with HashMap<TimeMonthTuple>, or compareTo(TimeMonthTuple) to make it work with TreeMap<TimeMonthTuple>

Is there a better way of doing this?

This is the most straightforward way, unless you have a class that can replace TimeMonthTuple with something that makes sense. For example, time and date could be combined into a Date object.

In certain cases you could make a key based on a primitive wrapper. For example, if time is expressed as the number of minutes since midnight and month is a number between 1 and 12, inclusive, you could wrap both values into an Integer, and use it as a key:

Integer makeTimeMonthKey(int time, int month) {
    return (time * 12) + (month - 1);
}