What does a "+=" operator inside a ternary operator means?

user_11214643 0
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I came across a code snippet inside the androidx.lifecycle package and I was wondering what does this means.

LiveData.this.mActiveCount += mActive ? 1 : -1;

Where mActiveCount is an int, and mActive is a boolean.

But, as I was writting this question, I think I came with the answer, so if I'm not mistaken the "+=" operator, is used as we normally use the "=" operator.

This means that the order in which the code executes is the following:

the mActive ? 1 : -1; portion executes first.

Once this is resolved, the LiveData.this.mActiveCount += mActive executes. So my real question is:

Is this the correct equivalence of this code?:

    int intToAdd = mActive ? 1 : -1;
    activeCount += intToAdd;
java
4 Answers

The operator += is not concerned with ternary operator. You are checking for a condition using ternary operator and incrementing or decrementing it variable by 1.

a = a + b is equivalent to a += b, assuming we have declared a and b previously.

So, your code LiveData.this.mActiveCount += mActive ? 1 : -1; is equivalent to :-

 if(mActive){
    LiveData.this.mActiveCount += 1;
 }
 else{
   LiveData.this.mActiveCount -= 1;
 }

Your Logic below is also correct:-

 int intToAdd = mActive ? 1 : -1;
 activeCount += intToAdd;
user_115883710

This line of code adds either 1 or -1 to mAtiveCount, and looks at the boolean mActive to determine whether it adds +1 or -1.

It is exactly equivalent to this chunk of code, where I removed the usage of the tertiary operator and the += operator (and made their function explicit):

int amountToAdd;
if (mActive) {
  amountToAdd = 1;
} else { 
  amountToAdd = -1;
}
LiveData.this.mActiveCount = LiveData.this.mActiveCount + amountToAdd;

I think the line is a bit unclear, but could be made more clear with the judicious use of parenthesis:

LiveData.this.mActiveCount += (mActive ? 1 : -1);

user_612480

Yes, you are right. There is something called as shorthand in java .

For example :

sum = sum + 1 can be written as sum += 1.

This statement :

LiveData.this.mActiveCount += mActive ? 1 : -1;

This statement really mean to say :

Either do this LiveData.this.mActiveCount += 1 or LiveData.this.mActiveCount += -1 based on mActive's value (true or false)

user_83409970

This can be answered by looking up Java operator precedence.

Assignment operators have the absolute lowest precedence, everything else happens first. The conditional expression mActive ? 1 : -1 is evaluated first. then the += is evaluated using the result of the condition expression.

user_2173240
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