A specialized implementation of the
based on an
This class maintains a member field of type
implements the following algorithm to create and initialize an object in its
- First it is checked whether the
AtomicReference variable contains
already a value. If this is the case, the value is directly returned.
- Otherwise the
#initialize() method is called. This method must be
defined in concrete subclasses to actually create the managed object.
- After the object was created by
#initialize() it is checked
AtomicReference variable is still undefined. This has to
be done because in the meantime another thread may have initialized the
object. If the reference is still empty, the newly created object is stored
in it and returned by this method.
- Otherwise the value stored in the
AtomicReference is returned.
Because atomic variables are used this class does not need any
synchronization. So there is no danger of deadlock, and access to the managed
object is efficient. However, if multiple threads access the
AtomicInitializer object before it has been initialized almost at the same
time, it can happen that
#initialize() is called multiple times. The
algorithm outlined above guarantees that
#get() always returns the
same object though.
Compared with the
LazyInitializer class, this class can be more
efficient because it does not need synchronization. The drawback is that the
#initialize() method can be called multiple times which may be
problematic if the creation of the managed object is expensive. As a rule of
thumb this initializer implementation is preferable if there are not too many
threads involved and the probability that multiple threads access an
uninitialized object is small. If there is high parallelism,
LazyInitializer is more appropriate.