增量运算符如何在Java中运行？

Question

Why is the result 8 and not 9?

By my logic:

1. ++x gives 4
2. 4 + 4 gives 8, so x = 8
3. But after that statement x should be increased due to x++ , so it should be 9.

What's wrong with my logic?:

int x = 3;
x = x++ + ++x;
System.out.println(x); // Result: 8 

Answer 1

You should note that the expression is evaluated from the left to the right :

First x++ increments x but returns the previous value of 3.

Then ++x increments x and returns the new value of 5 (after two increments).

x = x++ + ++x;
    3   +  5     = 8

However, even if you changed the expression to

x = ++x + x++;

you would still get 8

x = ++x + x++
     4  +  4   = 8

This time, the second increment of x ( x++ ) is overwritten once the result of the addition is assigned to x.

Answer 2

++x is called preincrement and x++ is called postincrement. x++ gives the previous value and ++x gives the new value.