Follow-up: Find sum of number of times that each character of source occurs in the target
Sorry, but this looks worse. I guess, you've been confused by the different ideas presented in the answers. And I am, confused, too. I don't understand it, so just some minor comments:

//reset the single counter


This is a sign that you've defined the counter in a wrong scope. Define it inside of the loop.



tempMap, temp... everything is temporary, we too. But this doesn't mean that it can't be properly named. Or removed... you need no temp String anymore.



I think I sort of understand it. The tempMap keeps track of the number of occurrences per character. So name it like it....

I don't think it really works. However, why not use a Set to keep track of what chars you've seen already? The logic is then trivial: "already seen -> skip it".

Enough for now.