Pre/Post increment query

Question

I have a query regarding Pre/Post increment.
The following code:
int x = 0;
int y = 0;
x += y++;
System.out.println("x = " + x);
System.out.println("y = " + y);
Produces the following output:
x = 0
y = 1
(Value of y is assigned to x, y is then post incremented).
This makes sense to me. However the following code,
the value of x does not get incremented. Can someone
explain this to me?
The following code:
int x = 0;
x += x++;
System.out.println("x = " + x);
Produces the following output:
x = 0
(Value of x is assigned to x, then x does not get post incremented??).

Answer 1

I code with the mind set of "If the code is not self explanatory or obvious, then
it's too confusing and should be avoided".
I am studying for the Java Programmer Certification exam, so this query was more
to try and understand why the output did not match what I had expected.
So
x += x++;
is the same as (where x' refers to the original value of x)
x = (x) + (x++);
which is then executed in the following order:
x = x++; //(x = x + 1) post incrementation
x = x' + x'; //(x = 0 + 0) evalutation of the assignment
Thanks for all the responses!!