IntelliJ IDEA underlines variables when using += in JAVA

Question

Since the new update (2018.2) IntelliJ IDEA underlines variables, when they are \"unnecessarily\" reassigned - this includes, however, each use of \"+=\".
Is this a mistake

Answer 1

If you know what is the side effect in programming then it will be easy for you. To protect your variable from the side effect, the IDE shows the underline as a warning to you.