Interface Worker<V>
- All Known Implementing Classes:
WorkerImpl
A Worker is an object which performs some work in one or more background
threads, and whose state is observable and available to JavaFX applications
and is usable from the main JavaFX Application thread. This interface is
primarily implemented by both Task
and Service
, providing
a common API among both classes which makes it easier for libraries and
frameworks to provide workers which work well when developing user interfaces.
A Worker may or may not be reusable depending on the implementation. A
Task
, for example, is not reusable while a Service
is.
A Worker has a well defined life cycle. Every Worker begins in the
Worker.State.READY
state. When the Worker has been scheduled for work
(for example, when a Service's Service.start()
method is called), it is transitioned to Worker.State.SCHEDULED
. Even
Workers which are not technically scheduled, but started immediately
(such as with FutureTask.run()
) will transition through
the Worker.State.SCHEDULED
on its way to the Worker.State.RUNNING
state.
When the Worker is actually performing its work, the state will have been
transitioned to Worker.State.RUNNING
. If the Worker completes normally,
it will end in the Worker.State.SUCCEEDED
state, and the result of the
Worker will be set as the value
property. If however an Exception
occurs during the execution of the Worker, then the state will be set to
Worker.State.FAILED
and the exception
property will be set
to the Exception which occurred.
At any time prior to the conclusion of the Worker (that is, if the state
is not already Worker.State.SUCCEEDED
or Worker.State.FAILED
) the developer
may invoke the
invalid @link
javafx.concurrent.Worker#cancel()
Worker.State.CANCELLED
.
The only valid beginning state for a Worker is Worker.State.READY
, and the
valid ending states are Worker.State.CANCELLED
, Worker.State.SUCCEEDED
,
and Worker.State.FAILED
. The running
property is set to
true when the state is either Worker.State.SCHEDULED
or Worker.State.RUNNING
.
The Worker's progress can be monitored via three different properties,
totalWork
, workDone
, and progress
.
These properties are set by the actual implementation of the Worker
interface, but can be observed by anybody. The workDone
is
a number between -1 (meaning indeterminate progress) and
totalWork
, inclusive. When workDone == totalWork
the progress
will be 100% (or 1). totalWork
will be a number between -1 and Long.MAX_VALUE, inclusive. The progress
will be either -1 (meaning indeterminate), or a value between 0 and 1, inclusive,
representing 0% through 100%.
A Worker which is in the Worker.State.READY
or Worker.State.SCHEDULED
states
will always have workDone
and progress
set to -1.
A Worker which is in the Worker.State.SUCCEEDED
state will always have
workDone == totalWork
and progress == 1
. In any
other state, the values for these properties may be any value in their
respective valid ranges.
- Since:
- JavaFX 2.0
-
Property Summary
PropertiesTypePropertyDescriptionGets the ReadOnlyObjectProperty representing the current state. -
Nested Class Summary
Nested Classes -
Method Summary
Modifier and TypeMethodDescriptiongetState()
Specifies the current state of this Worker.Gets the ReadOnlyObjectProperty representing the current state.
-
Property Details
-
state
ReadOnlyObjectProperty<Worker.State> statePropertyGets the ReadOnlyObjectProperty representing the current state.- See Also:
-
-
Method Details
-
getState
Worker.State getState()Specifies the current state of this Worker. The initial value is State.READY. A Task may be restarted, in which case it will progress from one of these end states (SUCCEEDED, CANCELLED, or FAILED) back to READY and then immediately to SCHEDULED and RUNNING. These state transitions may occur immediately one after the other, but will always occur in the prescribed order.- Returns:
- The current state of this Worker
-
stateProperty
ReadOnlyObjectProperty<Worker.State> stateProperty()Gets the ReadOnlyObjectProperty representing the current state.- Returns:
- The property representing the state
- See Also:
-