Order of operations for compound assignment operators in Java

Question

I came across the following on a mock exam recently, and was a bit lost as to why the answer given is 25, 25 according to the order of operations, and what I mi

Answer 1

In this answer, I will only consider the k case, it is the same for the array.

int k = 1;
k += (k = 4) * (k + 2);
// k += (k = 4) * (k + 2)
// 1 += (k = 4) * (k + 2)
// 1 +=    4    * (k + 2) with k = 4
// 1 +=    4    *   6     with k = 4
// k = 25

The tricks here:

• k += captures the value of k before doing the calculation. += is called a compound assignment operator. Quoting the relevant part of the JLS:

  the value of the left-hand operand is saved and then the right-hand operand is evaluated.

• k = 4 returns the assigned value, so 4.