What is the runtime class of an object ?

[Razvan]

Hi !






Static synchronized methods are synchronizing on the runtime class of
an object. From the official documentation:

getClass()
public final Class getClass()Returns the runtime class of an object.
That Class object is the object that is locked by static synchronized
methods of the represented class.

Returns:
the object of type Class that represents the runtime class of the
object.


So, this runtime class object is a hidden object that is created only
when there is a static and synchronized method ? Aside from
synchronizing static methods I see no use for this object. Is it true
that this object is dedicated to synchronization ?



Regards,
Razvan

 

[Michael Borgwardt]

Static synchronized methods are synchronizing on the runtime class of
an object. From the official documentation:

getClass()
public final Class getClass()Returns the runtime class of an object.
That Class object is the object that is locked by static synchronized
methods of the represented class.

Returns:
the object of type Class that represents the runtime class of the
object.


So, this runtime class object is a hidden object that is created only
when there is a static and synchronized method ? Aside from
synchronizing static methods I see no use for this object. Is it true
that this object is dedicated to synchronization ?

No. I think you're completely misunderstanding the API docs. The class
object in question is *always* present for every class that is loaded.
Since it is unique for each class, it is also just the right thing to
be used by static (i.e. per-class) code to synchronize on, so the
language designers choose to use it that way for the 'synchronized'
method modifier.

 

[Tor Iver Wilhelmsen]

So, this runtime class object is a hidden object that is created only
when there is a static and synchronized method ?

No; it's the "metaclass" object (instance of java.lang.Class)
associated with the class. It's available at all times as long as the
class is loaded. Can also be obtained using Class.forName() or the
automagic reference SomeType.class.

Aside from synchronizing static methods I see no use for this
object. Is it true that this object is dedicated to synchronization
?

No. Take a look at its class (java.lang.Class) for a host of methods
used for e.g. reflection/introspection.