Unexpected post-increment result

Question

so im currently working my way becoming a java developer, im starting with testing the basic stuff and when i was testing the post increment operator i stumbled upon some unexpected result.

The code goes like this:

public static void main(String[] args) {

    int intVar1 = 10;
    int intVar2 = 20;
    short shortSum = (short) (intVar1 + intVar2);
    short shortSum2 = shortSum++;

    System.out.println(shortSum);
    System.out.println(shortSum2);

}

The result displayed in the terminal is:

31 30

Question is, shouldnt it display the values the other way around? Shouldnt the shortSum variable be 30 and shortSum2 be 31?