The TIOBE Index uses this methodology to gauge the popularity of software languages. According to the latest measure:

• Java has swapped places with C, moving from number 2 in January 2015 to number 1 this month.
• Objective-C has moved from number 3 all the way down to number 18, one year later.
• Swift has risen from number 25 to number 14.
• C++ has moved from 4 to 3.
• Python has moved from 8 to 5.

An interesting comment from the article:

Java’s rise goes hand in hand with Objective-C’s decline (-5.88%). Apple’s announcement to replace Objective-C by Swift some time ago was the main cause of this fall. It was expected that Swift would gain as much popularity as Objective-C left behind, but that doesn’t appear to be the case. This is also observed in practice: TIOBE’s customers are not eagerly migrating to Swift yet.

I would have expected Swift plus Objective-C usage to be a near constant. Any fall in Objective-C would see a corresponding rise in Swift. That doesn’t appear to be the case.

Interesting.

UPDATE: You might also want to take a look at the annual Stack Overflow developer survey, found here. [H/T Eric Jacobson]