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Is there a difference between synchronized (UserDefine.class) and synchronized (define1.getClass ())?

I am learning Java MutliThread these days, I came across a problem. Is there a difference between synchronized (UserDefine.class) and synchronized (define1.getClass ())?

define1 is an instance of UserDefine class.

Thank you in advance:)

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2 answers


If it define1

stores a reference to an object of a specific type UserDefine

, there is no difference. Both expressions

UserDefine.class

and



define1.getClass()

will result in the same instance Class

. Therefore, there would be no difference.

If define1

stores a reference to an object of any other type (or null

) then there will be a difference. The corresponding thread will block the monitor on another object or will NullPointerException

(for the case null

).

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Small difference:



UserDefine.class

always refers to a UserDefine.class object define1.getClass();

may, in your case, always return UserDefine.class, but often in programming, if you or someone else comes later, perhaps subclassing UserDefine, in your code it may not return what you expect.

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