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@Synchronized

synchronized done right: Don't expose your locks.

Overview

+ @Synchronized is a safer variant of the synchronized method modifier. Like synchronized, the + annotation can be used on static and instance methods only. It operates similarly to the synchronized keyword, but it locks + on different objects. The keyword locks on this, but the annotation locks on a field named $lock, which is private.
+ If the field does not exist, it is created for you. If you annotate a static method, the annotation locks on a static field + named $LOCK instead. +

+ If you want, you can create these locks yourself. The $lock and $LOCK fields will of course not be generated if you + already created them yourself. You can also choose to lock on another field, by using specifying it as parameter to the @Synchronized + annotation. In this usage variant, the fields will not be created automatically, and you must explicitly create them yourself. +

+ Locking on this or your own class object can have unfortunate side-effects, as other code not under your control can lock on these + objects as well, which can cause race conditions and other nasty threading-related bugs. +

With Lombok

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Vanilla Java

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Small print

+ If $lock and/or $LOCK are auto-generated, the fields are initialized with an empty Object[] array, and not + just a new Object() as most snippets showing this pattern in action use. Lombok does this because a new object is NOT + serializable, but 0-size array is. Therefore, using @Synchronized will not prevent your object from being serialized. +

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