CODEWITHSUNDEEP
javamathoperators
alexg2021
alexg2021

Reputation: 313

=+ Operator in Java

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.

Upvotes: 10

Views: 602

Answers (4)

Moha the almighty camel
Moha the almighty camel

Reputation: 4483

if the operator used was += you will be adding to val the value of i+1.

in your case you are assigning to val the value of i+1 each time, on the final iteration i = 2 so val = 3.

Upvotes: 0

rgettman
rgettman

Reputation: 178323

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.

Upvotes: 18

alexg2021
alexg2021

Reputation: 313

Corrected calculation:

val   i
0     0  i<2 = true;
0     0  ++i;
0     1  val = +i = 1;
1     1  (end of for loop) val++;
2     1  i<2 = true;
2     1  ++i;
2     2  val = +i = 2;
2     2  (end of for loop) val++;
3     2  i<2 = false;
Output: 3

Upvotes: 0

0x6B6F77616C74
0x6B6F77616C74

Reputation: 2630

There is no =+ operator in Java, according to the official documentation. Use += instead to get desired effect.

Upvotes: 0

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