Automatically catching the use of =+ rather than += in Java

Question

I have this horrible habit of typing the below and not catching it until well into testing:

int i = 1;
int j = 2;
i =+ j;  //i equals 2, not 3 as intended; assign only, + is unary and works on the j

The correct version, of course, would be

int i = 1;
int j = 2;
i += j;  //i equals 3, as intended with additive & assignment compound operator

I have made this mistake a zillion times. It would not surprise me of there is some code out there with a bug in it that escaped a test case. There has just got to be a way to prevent this systematically. Any ideas?

Answer 1

I think you have to be rigorous in your unit testing. At the moment you're worried about one particular issue, but good unit tests will capture most issues (ignoring threading/loading etc.).

You have to decompose your classes/methods such that you can test each chunk of functionality and ensure complete (or as near as you can) coverage.

Clover (commercial) or Emma (open source) will manage code coverage for you.

Answer 2

Regularly use tools like PMD and/or Checkstyle. Ideally as part of your build process/continuous integration.

You might have to define a custom rule for this, because I don't know if any of those tools recognizes this as a problem by default.

This will not only catch this problem, but also hint at a lot of other potential problems as well.

Answer 3

Use standard text utilities, such as

find . -name \*.java -exec grep -H "=+" {} \;

Answer 4

Depending on what IDE you use, if it does syntax highlighting, I would modify the highlighting so that it looks for the pattern =+ and makes it some awful-to-look-at color.

Answer 5

As balpha commented, an easy way to find this would be to grep for the "=+" in code. It is probably never intentional.