SynchronizedOnLiteralObject

Reports synchronized blocks that lock on an object initialized with a literal.

String literals are interned and Character, Boolean and Number literals can be allocated from a cache. Because of this, it is possible that some other part of the system, which uses an object initialized with the same literal, is actually holding a reference to the exact same object. This can create unexpected dead-lock situations, if the lock object was thought to be private.

Example:

class Main {
    final String mutex = "Mutex";
    void method() {
      synchronized (mutex) {
      }
    }
  }

Use the Warn on all possible literals option to report any synchronization on String, Character, Boolean and Number objects.