Package org.eclipse.core.databinding.observable.set

Class ComputedSet<E>

  • Type Parameters:
    E - the type of the elements in this set
    All Implemented Interfaces:
    Iterable<E>, Collection<E>, Set<E>, IObservable, IObservableCollection<E>, IObservableSet<E>
    public abstract class ComputedSet<E>
extends AbstractObservableSet<E>
    A lazily calculated set 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 set 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 set of all primes greater than 1 and less than the value of an IObservableValue < Integer >. 

     final IObservableValue max = WritableValue.withValueType(Integer.TYPE);
 max.setValue(Integer.valueOf(0));
 IObservableSet primes = new ComputedSet() {
        protected Set calculate() {
                int maxVal = ((Integer) max.getValue()).intValue();

                Set result = new HashSet();
                outer: for (int i = 2; i < maxVal; i++) {
                        for (Iterator it = result.iterator(); it.hasNext();) {
                                Integer knownPrime = (Integer) it.next();
                                if (i % knownPrime.intValue() == 0)
                                        continue outer;
                        }
                        result.add(Integer.valueOf(i));
                }
                return result;
        }
 };

 System.out.println(primes); // => "[]"

 max.setValue(Integer.valueOf(20));
 System.out.println(primes); // => "[2, 3, 5, 7, 11, 13, 17, 19]"
    Since:
    1.2

    • Constructor Detail

      • ComputedSet

        public ComputedSet()
        Creates a computed set in the default realm and with an unknown (null) element type.

      • ComputedSet

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

      • ComputedSet

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

      • ComputedSet

        public ComputedSet​(Realm realm,
                   Object elementType)
        Creates a computed set 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

      • doGetSize

        protected int doGetSize()

      • calculate

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

      • 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 AbstractObservableSet<E>
        Returns:
        Returns the stale state.

      • 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 element type 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 AbstractObservable
        Parameters:
        listener - the listener to add; not null

      • 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 AbstractObservable

      • addListener

        protected void addListener​(Object listenerType,
                           IObservablesListener listener)
        Parameters:
        listenerType - arbitrary object to identify a type of the listener
        listener - the listener to add; not null

      • removeListener

        protected void removeListener​(Object listenerType,
                              IObservablesListener listener)
        Parameters:
        listenerType - arbitrary object to identify a type of the listener
        listener - the listener to remove; not null

      • hasListeners

        protected boolean hasListeners()

      • firstListenerAdded

        protected void firstListenerAdded()

      • lastListenerRemoved

        protected void lastListenerRemoved()

      • getRealm

        public Realm getRealm()
        Returns:
        Returns the realm.