Module javafx.graphics
Package javafx.concurrent

Interface Worker<V>

  • All Known Implementing Classes:
    ScheduledService, Service, Task
    public interface Worker<V>

    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 cancel() method. If called, the Worker will cease execution (if possible, including use of Thread.interrupt) and the state changed to 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

    • Method Detail

      • 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

      • getValue

        V getValue()
        Specifies the value, or result, of this Worker. This is set upon entering the SUCCEEDED state, and cleared (set to null) if the Worker is reinitialized (that is, if the Worker is a reusable Worker and is reset or restarted).
        Returns:
        the current value of this Worker

      • getException

        Throwable getException()
        Indicates the exception which occurred while the Worker was running, if any. If this property value is null, there is no known exception, even if the status is FAILED. If this property is not null, it will most likely contain an exception that describes the cause of failure.
        Returns:
        the exception, if one occurred

      • getWorkDone

        double getWorkDone()
        Indicates the current amount of work that has been completed. Zero or a positive value indicate progress toward completion. This variables value may or may not change from its default value depending on the specific Worker implementation. A value of -1 means that the current amount of work done cannot be determined (ie: it is indeterminate). The value of this property is always less than or equal to totalWork.
        Returns:
        the amount of work done
        See Also:
        totalWorkProperty(), progressProperty()

      • getTotalWork

        double getTotalWork()
        Indicates a maximum value for the workDoneProperty() property. The totalWork will either be -1 (indicating that the amount of work to do is indeterminate), or it will be a non-zero value less than or equal to Double.MAX_VALUE.
        Returns:
        the total work to be done
        See Also:
        workDoneProperty(), progressProperty()

      • totalWorkProperty

        ReadOnlyDoubleProperty totalWorkProperty()
        Gets the ReadOnlyDoubleProperty representing the maximum amount of work that needs to be done. These "work units" have meaning to the Worker implementation, such as the number of bytes that need to be downloaded or the number of images to process or some other such metric.
        See Also:
        getTotalWork()

      • getProgress

        double getProgress()
        Indicates the current progress of this Worker in terms of percent complete. A value between zero and one indicates progress toward completion. A value of -1 means that the current progress cannot be determined (that is, it is indeterminate). This property may or may not change from its default value of -1 depending on the specific Worker implementation.
        Returns:
        the current progress
        See Also:
        workDoneProperty(), totalWorkProperty()

      • isRunning

        boolean isRunning()
        True if the state is either SCHEDULED or RUNNING. When binding a Worker to a ProgressIndicator, you will typically bind the visibility of the ProgressIndicator to the Worker's running property, and the progress of the ProgressIndicator to the Worker's progress property.
        Returns:
        true if this Worker is running

      • getMessage

        String getMessage()
        Gets a message associated with the current state of this Worker. This may be something such as "Processing image 1 of 3", for example.
        Returns:
        the current message

      • getTitle

        String getTitle()
        An optional title that should be associated with this Worker. This may be something such as "Modifying Images".
        Returns:
        the current title

      • cancel

        boolean cancel()
        Terminates execution of this Worker. Calling this method will either remove this Worker from the execution queue or stop execution.
        Returns:
        returns true if the cancel was successful