在Java中使用“ + =”代替“ =”的目的是什么？

Question

So I ran into this piece of code today while working on an existing codebase. My question is why the assignment operator was not used here.

  int getSum(int mVar) {
      int sum = 0;
      sum += ((mVar != null) ? mVar : 0);
      return sum;
    }

It appears an assignment operator would suffice:

int getSum(int mVar) {
      int sum = ((mVar != null) ? mVar : 0);
      return sum;
    }

Is there any benefit to initializing the value to zero?

Answer 1

This

int getSum(int mVar) {
    int sum = 0;
    sum += ((mVar != null) ? mVar : 0);
    return sum;
}

is the same as

int getSum(int mVar) {
    int sum = 0;
    if( mVar != null ) {
        sum = sum + mVar;
    } else {
        sum = sum + 0;
    }
    return sum;
}

It's just full of shorthand code. :)

As many of the comments mentioned, a += b is just the same as a = a + b . It's a nifty trick to have. The same also applies for a -= b , a *= b , and a /= b .

If you were curious, (mVar != null) ? mVar : 0; (mVar != null) ? mVar : 0; is a ternary operator. It goes like condition ? value if true : value if false; condition ? value if true : value if false; and is usually used for assignments.

Some notes though. An int is a primitive data type that can never be null, so the code above is just for the sake of explaining syntax.

Answer 2

To answer your question, in this example there is no point in using "+=", a regular assignment operator is better

 int getSum(int mVar) {
      int sum = 0;
      sum += ((mVar != null) ? mVar : 0);
      return sum;
 }

This code is a bad example of "+=" because it shouldn't be used here. Instead it should be:

   int getSum(Integer mVar) {
          return mVar != null? mvar : 0;
   }

You don't see the benefit of "+=" because sum is already 0 . So, you look at it and you're wondering why you would do sum = 0 + mVar; (which is the same as saying sum += mVar when you can do sum = mVar;

A better example is (ofc these values probably don't make sense, but it makes the "+=" valuable):

  int getSum(int mVar) {
          int sum = 5;
          sum += ((mVar != null) ? mVar : 10);
          return sum;
     }

This way if you don't use "+=" you are forced in saying sum = sum + mVar; or else it wouldn't be correct.