Class FutureResult


  • public class FutureResult
    extends java.lang.Object
    A class maintaining a single reference variable serving as the result of an operation. The result cannot be accessed until it has been set.

    Sample Usage

     class ImageRenderer { Image render(byte[] raw); }
     class App {
       Executor executor = ...
       ImageRenderer renderer = ...
       void display(byte[] rawimage) {
         try {
           FutureResult futureImage = new FutureResult();
           Runnable command = futureImage.setter(new Callable() {
              public Object call() { return renderer.render(rawImage); }
           });
           executor.execute(command);
           drawBorders();             // do other things while executing
           drawCaption();
           drawImage((Image)(futureImage.get())); // use future
         }
         catch (InterruptedException ex) { return; }
         catch (InvocationTargetException ex) { cleanup(); return; }
       }
     }
     

    [ Introduction to this package. ]

    See Also:
    Executor
    • Field Summary

      Fields 
      Modifier and Type Field Description
      protected java.lang.reflect.InvocationTargetException exception_
      the exception encountered by operation producing result
      protected boolean ready_
      Status -- true after first set
      protected java.lang.Object value_
      The result of the operation
    • Constructor Summary

      Constructors 
      Constructor Description
      FutureResult()
      Create an initially unset FutureResult
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Clear the value and exception and set to not-ready, allowing this FutureResult to be reused.
      protected java.lang.Object doGet()
      internal utility: either get the value or throw the exception
      java.lang.Object get()
      Access the reference, waiting if necessary until it is ready.
      java.lang.reflect.InvocationTargetException getException()
      Get the exception, or null if there isn't one (yet).
      boolean isReady()
      Return whether the reference or exception have been set.
      java.lang.Object peek()
      Access the reference, even if not ready
      void set​(java.lang.Object newValue)
      Set the reference, and signal that it is ready.
      void setException​(java.lang.Throwable ex)
      Set the exception field, also setting ready status.
      java.lang.Runnable setter​(Callable function)
      Return a Runnable object that, when run, will set the result value.
      java.lang.Object timedGet​(long msecs)
      Wait at most msecs to access the reference.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Field Detail

      • value_

        protected java.lang.Object value_
        The result of the operation
      • ready_

        protected boolean ready_
        Status -- true after first set
      • exception_

        protected java.lang.reflect.InvocationTargetException exception_
        the exception encountered by operation producing result
    • Constructor Detail

      • FutureResult

        public FutureResult()
        Create an initially unset FutureResult
    • Method Detail

      • setter

        public java.lang.Runnable setter​(Callable function)
        Return a Runnable object that, when run, will set the result value.
        Parameters:
        function - - a Callable object whose result will be held by this FutureResult.
        Returns:
        A Runnable object that, when run, will call the function and (eventually) set the result.
      • doGet

        protected java.lang.Object doGet()
                                  throws java.lang.reflect.InvocationTargetException
        internal utility: either get the value or throw the exception
        Throws:
        java.lang.reflect.InvocationTargetException
      • get

        public java.lang.Object get()
                             throws java.lang.InterruptedException,
                                    java.lang.reflect.InvocationTargetException
        Access the reference, waiting if necessary until it is ready.
        Returns:
        current value
        Throws:
        java.lang.InterruptedException - if current thread has been interrupted
        java.lang.reflect.InvocationTargetException - if the operation producing the value encountered an exception.
      • timedGet

        public java.lang.Object timedGet​(long msecs)
                                  throws TimeoutException,
                                         java.lang.InterruptedException,
                                         java.lang.reflect.InvocationTargetException
        Wait at most msecs to access the reference.
        Returns:
        current value
        Throws:
        TimeoutException - if not ready after msecs
        java.lang.InterruptedException - if current thread has been interrupted
        java.lang.reflect.InvocationTargetException - if the operation producing the value encountered an exception.
      • set

        public void set​(java.lang.Object newValue)
        Set the reference, and signal that it is ready. It is not considered an error to set the value more than once, but it is not something you would normally want to do.
        Parameters:
        newValue - The value that will be returned by a subsequent get();
      • setException

        public void setException​(java.lang.Throwable ex)
        Set the exception field, also setting ready status.
        Parameters:
        ex - The exception. It will be reported out wrapped within an InvocationTargetException
      • getException

        public java.lang.reflect.InvocationTargetException getException()
        Get the exception, or null if there isn't one (yet). This does not wait until the future is ready, so should ordinarily only be called if you know it is.
        Returns:
        the exception encountered by the operation setting the future, wrapped in an InvocationTargetException
      • isReady

        public boolean isReady()
        Return whether the reference or exception have been set.
        Returns:
        true if has been set. else false
      • peek

        public java.lang.Object peek()
        Access the reference, even if not ready
        Returns:
        current value
      • clear

        public void clear()
        Clear the value and exception and set to not-ready, allowing this FutureResult to be reused. This is not particularly recommended and must be done only when you know that no other object is depending on the properties of this FutureResult.