为什么我们使用Object作为同步锁？

Question

Does it provide any benefit over using lock on String etc?

private Object lock = new Object();

private String lock = new String();

Answer 1

Any class would do. Using Object makes sense because it is the smallest and simplest object you can create. Anything else would be "too much".

Answer 2

Like others have said, there's really no difference between using a String or an Object for your lock, though some would say one is more 'wasteful' of memory than another. If your looking for some good synchronization 'primitives' though then it's worth taking a look at the Java Concurrency packages , theres actually a Lock object that has alot of useful methods you can utilize.

Answer 3

Generally you do not want to use String objects as locks for synchronization. The reason is that the JVM can optimize memory used for storing Strings by interning them because Strings are immutable. This can potentially cause unrelated parts of your system to 'share' a lock that was never intended to be shared. This can manifest itself as simply non optimal performance or in the worst case deadlocks from a race condition that is non-obvious without a debugger.

This also applies for other Object primitive equivalents that are optimized such as Integer, Long, and Boolean. You do not want to use them as locks, as again for example all Boolean objects with the value true could actually be references to the same single instance of Boolean.TRUE.

This issue is explained further in the link below.

LCK01-J. Do not synchronize on objects that may be reused

Answer 4

No it doesn't. It's just that you explicitly say it's just an Object having no other sense than being used for locking—while String is a string, and an empty String is still a meaningful entity.

Answer 5

No.

Any object is equally suitable.