Package org.eclipse.core.databinding.observable.list

Class ComputedList<E>

java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractList<E>
org.eclipse.core.databinding.observable.list.AbstractObservableList<E>
org.eclipse.core.databinding.observable.list.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 Details

    • 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 Details

    • create

      public static <E> IObservableList<E> create(Supplier<List<E>> supplier)
      Factory method to create ComputedList objects in an easy manner.

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

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

    • doGetSize

      protected int doGetSize()
      Specified by:
      doGetSize in class AbstractObservableList<E>
      Returns:
      the size

    • get

      public E get(int index)
      Specified by:
      get in interface IObservableList<E>
      Specified by:
      get in interface List<E>
      Specified by:
      get in class AbstractList<E>

    • 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>
      Parameters:
      listener - the listener to add; not null

    • addListChangeListener

      public void addListChangeListener(IListChangeListener<? super E> listener)
      Description copied from interface: IObservableList
      Adds the given list change listener to the list of list change listeners.
      Specified by:
      addListChangeListener in interface IObservableList<E>
      Overrides:
      addListChangeListener in class AbstractObservableList<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 AbstractObservableList<E>