Java i++ operation explanation [duplicate]

Answer 1

When the ++ operator appears after the variable, as in your example i++, the increment of i, happens after the operation is over. that's why the first print in the first example is zero, you haven't added yet, and then second one is 1.

the second example is the same as saving i, then incremeting it, and placing the original back.

i++

is an operator itself.

You could experiment the first one with ++i which will increase i before doing the printing action

Answer 2

i = i++; is the tricky construct, what it really does is something like the following:

int iOld = i;
i = i + 1;
i = iOld;

You want to use only i++; as a standalone statement.

Answer 3

The statement i = i++ has well-defined behavior in Java. First, the value of i is pushed on a stack. Then, the variable i is incremented. Finally, the value on top the stack is popped off and assigned into i. The net result is that nothing happens -- a smart optimizer could remove the whole statement.