What is the difference between -= and =-?

Question

In java and other languages I’ve seen in some projects things like:

saldo -= 100 and sometimes saldo =- 100 but I could never understand the difference between those two guys, if there’s any difference.

After all, there is some difference between performing an operation with -= and =- ?

Answer 1

saldo -= 100 is the same thing as saldo = saldo - 100.

saldo =- 100 is assigning -100 to the variable saldo. It’s clearer to visualize like this:

saldo = -100

Answer 2

Hello! I know that your doubt has been solved by friends. I will only share one more explanation about it, as it is the one I usually pass when someone asks me the same question. Then goes as "a complement" to the above answers.

Behold:

saldo = 500;
saldo -= 100;

System.out.println(saldo);

Output window prints:

run:
400

In this next logic, the first assignment in the value of 500, is no longer valid for variable balance and the account owner still had negative balance.

saldo = 500;
saldo =- 100;

System.out.println(saldo);

Output window prints:

run:
-100

Remembering that the account owner will also have negative balance, if done so:

saldo = 500;
saldo -= 600;

System.out.println(saldo);

Output window prints:

run:
-100

Answer 3

The operator -= java is used when we want to assign the value of a variable to subtract a second value from the current value of this variable.

Take this example:

int a -= b;

is the same as doing:

int a = a - b;

Already =- is not an operator, it is simply an assignment giving a negative signal to the value to be assigned to the right.

Answer 4

I think you understand the concept of increment and decrement wrong, see, in the first case you are actually decreasing the balance variable by -100, however; in the second case you are assigning the variable the value -100.

See the example below of a decrease:

class Teste {
    public static void main(String[] args) {
        int saldo = 14000;
        int i = 0;
        for(i=0; i < 5; i++) {
            saldo -= 100; //Aqui tem um decremento
            System.out.println("saldo : "+ saldo);
        }
    }
}

Its result is:

saldo : 13900
saldo : 13800
saldo : 13700
saldo : 13600
saldo : 13500

Now notice if you do the reverse, which is to put the sign - after the =assignment signal, getting sando =- 100

class Teste {
    public static void main(String[] args) {
        int saldo = 14000;
        int i = 0;
        for(i=0; i < 5; i++) {
            saldo =- 100; //Aqui tem uma atribuição, isto é, mesma coisa que saldo = -100;
            System.out.println("saldo : "+ saldo);
        }
    }
}

Result, was -100 in everything, because each loop the variable balance was assigned the value of -100:

saldo : -100
saldo : -100
saldo : -100
saldo : -100
saldo : -100