AssignmentToStaticFieldFromInstanceMethod

Reports assignment to, or modification of static fields from within an instance method.

Although legal, such assignments are tricky to do safely and are often a result of marking fields static inadvertently.

Example:

class Counter {
    private static int count = 0;

    void increment() {
      // Warning: updating a static field
      // from an instance method
      count++;
    }
  }