=+ Operator in Java

Question

Consider this code:

long val = 0;
for(int i = 0; i < 2; val++)
    val =+ ++i;

System.out.println(val);

Why is val = 3 in the end?

I would have calculated like this:

val     i
0       0   i < 2 = true;
0       0   ++i;
0       1   val =+ 1;
1       1   (end of for loop) val++;
2       1   i < 2 = true;
2       1   ++i;
2       2   val =+ 2;
4       2   (end of for loop) val++;
5       2   i < 2 = false;
Output: 5

But it's 3. I don't understand why the increment val =+ ++i is not done the second time when i = 1 and getting pre-incremented to i = 2.

Answer 1

Let's focus on the unusual-looking line first:

val =+ ++i;

The operators here are = (assignment), + (unary plus), and ++ (pre-increment). There is no =+ operator. Java interprets it as two operators: = and +. It's clearer with appropriate whitespace added:

val = + ++i;

Now let's analyze the processing:

First iteration: val and i are 0. i is pre-incremented to 1, and that's the result of ++i. The unary + does nothing, and 1 is assigned to val. Then the iteration statement val++ occurs and now val is 2. i is still 1, so the for loop condition is met and a second iteration occurs.

Second iteration: i is pre-incremented again, to 2. The unary + does nothing and val is assigned 2. The iteration statement val++ occurs again and it's now 3. But i is now 2, and it's not less than 2, so the for loop terminates, and val -- 3- is printed.