Can some pattern help here?

[Prasma Kankut]

Assume the following case:

The price to transport a shipment depends on 2 things
i) the distance from origin to destination and
ii) the weight of the shipment

For example,
If the transportation distance is less than 100 kms, the cost is 10$
If the transportation distance is between 100 and 200 kms, the cost is 20$
If the transportation distance is greater than 200 kms, the cost is 30$

If the shipment weight is less than 10 kgs, the cost is 10$
If the shipment weight is between 10 and 20 kgs, the cost is 20$
If the shipment weight is greater than 20 kgs, the cost is 30$

So, to transport a 50 kg shipment for 500 kms, the total cost is 60$.

Now, the shipment will have a getTotalCost() method, which will calculate the total cost, based on the above rules. It can be done with simple if/else checks, but ofcourse that is the worst way of doing.

Is there any pattern, which can help me here?

Strategy looks close, but I'm not sure. Any clues.

Many thanks

[Stan James]

I like Strategy but I almost always use fixed values to get a strategy from a map ... your ranges of values are a bit tougher.

For something this simple I'd probably just work through a collection of distance / rate pairs.

getRateForDistance( int distance )
{
   for each pair in pairCollection
      if distance < pair.distance
         return pair.value
   next
}

If you really must be objecty or if things got a bit more complex you could use a chain of widgets with this method:

getRateForDistance( int distance )
{
   if ( distance <= this.maxDistance )
      return this.rate
   else
      return nextWidget.getRateForDistance( distance )
}

I don't know if that's quite Chain Of Responsibility or not.

If your relationships are so neatly mathematical and you don't want to be at all objecty you could even do

int ix = distance / 100;
rate = rates[ix];

Any other thoughts?
[ January 05, 2006: Message edited by: Stan James ]

[Ilja Preuss]

Another "objecty" solution would be to replace

if distance < pair.distance

with

if pair.appliesTo(distance)

But it's most likely overkill, and easy to refactor to should it become valuable.