| Instances of boxed primitive types may be cached by the standard library |
| `valueOf` method. This method is used for autoboxing. This means that using a |
| boxed primitive as a lock can result in unintentionally sharing a lock with |
| another piece of code. |
| |
| Consider using an explicit lock `Object` instead of locking on a boxed |
| primitive. That is, prefer this: |
| |
| ```java |
| private final Object lock = new Object(); |
| |
| void doSomething() { |
| synchronized (lock) { |
| // ... |
| } |
| } |
| ``` |
| |
| instead of this: |
| |
| ```java |
| private final Integer lock = 42; |
| |
| void doSomething() { |
| synchronized (lock) { |
| // ... |
| } |
| } |
| ``` |
