Which code is heavy when being executed

Question

I'm comparing records based on their dates, if the date is equal to a particular month its data goes to a particular object. Example: If this the record is in the current month then it will be saved in the current month field. If the record is in the previous month then it will also be saved in the previous month field. Now, I have two sets of code snippets. Which is heavy when being executed:

First Snippet: (declaring variables)

DateTime prevDate = currentDate.AddMonths(-1),
                    nextDate = currentDate.AddMonths(1),
                    thirdDate = currentDate.AddMonths(2),
                    fourthDate = currentDate.AddMonths(3);

if (prevDate .Month == invoiceDetail.InvoiceDate.Month
     && prevDate.Year == invoiceDetail.InvoiceDate.Year)
{
   //code here
}

if (nextDate.Month == invoiceDetail.InvoiceDate.Month
     && nextDate.Year == invoiceDetail.InvoiceDate.Year)
{
   //code here
}

if (thirdDate.Month == invoiceDetail.InvoiceDate.Month
     && thirdDate.Year == invoiceDetail.InvoiceDate.Year)
{
   //code here
}

if (prevDate .Month == invoiceDetail.InvoiceDate.Month
     && prevDate.Year == invoiceDetail.InvoiceDate.Year)
{
   //code here
}

Second Snippet: (directly insert them in the if statement)

if (currentDate.AddMonths(-1).Month == invoiceDetail.InvoiceDate.Month
     && currentDate.AddMonths(-1).Year == invoiceDetail.InvoiceDate.Year)
{
   //code here
}

if (currentDate.AddMonths(1).Month == invoiceDetail.InvoiceDate.Month
     && currentDate.AddMonths(1).Year == invoiceDetail.InvoiceDate.Year)
{
   //code here
}

if (currentDate.AddMonths(2).Month == invoiceDetail.InvoiceDate.Month
     && currentDate.AddMonths(2).Year == invoiceDetail.InvoiceDate.Year)
{
   //code here
}

if (currentDate.AddMonths(3).Month == invoiceDetail.InvoiceDate.Month
     && currentDate.AddMonths(3).Year == invoiceDetail.InvoiceDate.Year)
{
   //code here
}

Answer 1

Other than some mistakes in the code (i.e. the year and month are not properties but methods), I'd say the 1st is the most efficient.

Even though in the 2nd snippet there's possibility for short-circuiting, the 2 conditions in each if() are based on the same evaluated date. So you need the dates to be already evaluated by default - can't take advantage of any short-circuit. (Read http://en.wikipedia.org/wiki/Short-circuit_evaluation if needed)

So the 1st approach is the way/the more efficient: with that, you "addMonths()" only once per condition, instead of doing it twice inline directly in the if().

Answer 2

I would be inclined to introduce local variables for invoiceDetail.InvoiceDate.Month and invoiceDetail.InvoiceDate.Year. It may be the case that the Apex compiler recognises that you are accessing the same prperties repeatedly, but then again, it may not.