Service-provider class for selectors and selectable channels.
A selector provider is a concrete subclass of this class that has a
zero-argument constructor and implements the abstract methods specified
below. A given invocation of the Java virtual machine maintains a single
system-wide default provider instance, which is returned by the
provider method. The first invocation of that method will locate
the default provider as specified below.
The system-wide default provider is used by the static open
methods of the
SocketChannel classes. It is also
used by the
method. A program may make use of a provider other than the default provider
by instantiating that provider and then directly invoking the open
methods defined in this class.
All of the methods in this class are safe for use by multiple concurrent threads.