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

Class ComputedSet<E>

java.lang.Object
org.eclipse.core.databinding.observable.AbstractObservable
org.eclipse.core.databinding.observable.set.AbstractObservableSet<E>
org.eclipse.core.databinding.observable.set.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 Details

    • 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 Details

    • create

      public static <E> IObservableSet<E> create(Supplier<Set<E>> supplier)
      Factory method to create ComputedSet objects in an easy manner.

      The created list has a null IObservableSet.getElementType().

      Parameters:
      supplier - Supplier, which is tracked using ObservableTracker to find out observables it uses, in the same manner as calculate().
      Returns:
      ComputedSet whose elements are computed using the given Supplier.
      Since:
      1.12

    • doGetSize

      protected int doGetSize()

    • getWrappedSet

      protected Set<E> getWrappedSet()
      Specified by:
      getWrappedSet in class AbstractObservableSet<E>

    • 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

    • addSetChangeListener

      public void addSetChangeListener(ISetChangeListener<? super E> listener)
      Specified by:
      addSetChangeListener in interface IObservableSet<E>
      Overrides:
      addSetChangeListener in class AbstractObservableSet<E>
      Parameters:
      listener - the change 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()

    • fireEvent

      protected void fireEvent(ObservableEvent event)

    • firstListenerAdded

      protected void firstListenerAdded()

    • lastListenerRemoved

      protected void lastListenerRemoved()

    • getRealm

      public Realm getRealm()
      Returns:
      Returns the realm.

    • clone

      protected Object clone() throws CloneNotSupportedException
      Overrides:
      clone in class Object
      Throws:
      CloneNotSupportedException