Class ComputedList<E>

  • Type Parameters:
    E - the list element type
    All Implemented Interfaces:
    Iterable<E>, Collection<E>, List<E>, IObservable, IObservableCollection<E>, IObservableList<E>

    public abstract class ComputedList<E>
    extends AbstractObservableList<E>
    A lazily calculated list that automatically computes and registers listeners on its dependencies as long as all of its dependencies are IObservable objects. Any change to one of the observable dependencies causes the list to be recomputed.

    This class is thread safe. All state accessing methods must be invoked from the current realm. Methods for adding and removing listeners may be invoked from any thread.

    Example: compute the fibonacci sequence, up to as many elements as the value of an IObservableValue < Integer >.

     final IObservableValue count = WritableValue.withValueType(Integer.TYPE);
     count.setValue(Integer.valueOf(0));
     IObservableList fibonacci = new ComputedList() {
            protected List calculate() {
                    int size = ((Integer) count.getValue()).intValue();
    
                    List result = new ArrayList();
                    for (int i = 0; i < size; i++) {
                            if (i == 0)
                                    result.add(Integer.valueOf(0));
                            else if (i == 1)
                                    result.add(Integer.valueOf(1));
                            else {
                                    Integer left = (Integer) result.get(i - 2);
                                    Integer right = (Integer) result.get(i - 1);
                                    result.add(Integer.valueOf(left.intValue() + right.intValue()));
                            }
                    }
                    return result;
            }
     };
    
     System.out.println(fibonacci); // => "[]"
    
     count.setValue(Integer.valueOf(5));
     System.out.println(fibonacci); // => "[0, 1, 1, 2, 3]"
     
    Since:
    1.1
    • Constructor Detail

      • ComputedList

        public ComputedList()
        Creates a computed list in the default realm and with an unknown (null) element type.
      • ComputedList

        public ComputedList​(Object elementType)
        Creates a computed list in the default realm and with the given element type.
        Parameters:
        elementType - the element type, may be null to indicate unknown element type
      • ComputedList

        public ComputedList​(Realm realm)
        Creates a computed list in given realm and with an unknown (null) element type.
        Parameters:
        realm - the realm
      • ComputedList

        public ComputedList​(Realm realm,
                            Object elementType)
        Creates a computed list in the given realm and with the given element type.
        Parameters:
        realm - the realm
        elementType - the element type, may be null to indicate unknown element type
    • Method Detail

      • calculate

        protected abstract List<E> calculate()
        Subclasses must override this method to calculate the list contents. Any dependencies used to calculate the list must be IObservable, and implementers must use one of the interface methods tagged TrackedGetter for ComputedList to recognize it as a dependency.
        Returns:
        the object's list.
      • isStale

        public boolean isStale()
        Description copied from interface: IObservable
        Returns whether the state of this observable is stale and is expected to change soon. A non-stale observable that becomes stale will notify its stale listeners. A stale object that becomes non-stale does so by changing its state and notifying its change listeners, it does not notify its stale listeners about becoming non-stale. Clients that do not expect asynchronous changes may ignore staleness of observable objects.
        Specified by:
        isStale in interface IObservable
        Overrides:
        isStale in class AbstractObservableList<E>
        Returns:
        true if this observable's state is stale and will change soon.
      • getElementType

        public Object getElementType()
        Description copied from interface: IObservableCollection
        Returns the element type of this observable collection, or null if this observable collection is untyped.
        Returns:
        the type of the elements or null if untyped
      • addChangeListener

        public void addChangeListener​(IChangeListener listener)
        Description copied from interface: IObservable
        Adds the given change listener to the list of change listeners. Change listeners are notified about changes of the state of this observable in a generic way, without specifying the change that happened. To get the changed state, a change listener needs to query for the current state of this observable.
        Specified by:
        addChangeListener in interface IObservable
        Overrides:
        addChangeListener in class AbstractObservableList<E>
      • dispose

        public void dispose()
        Description copied from interface: IObservable
        Disposes of this observable object, removing all listeners registered with this object, and all listeners this object might have registered on other objects.
        Specified by:
        dispose in interface IObservable
        Overrides:
        dispose in class AbstractObservableList<E>