org.eclipse.core.databinding.observable.value
Class ComputedValue

java.lang.Object
  

org.eclipse.core.databinding.observable.AbstractObservable
      

org.eclipse.core.databinding.observable.value.AbstractObservableValue
          
org.eclipse.core.databinding.observable.value.ComputedValue

All Implemented Interfaces:

IObservable, IObservableValue

Direct Known Subclasses:

AggregateValidationStatus

public abstract class ComputedValue
extends 
AbstractObservableValue

A Lazily calculated value 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 value 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 sum of all elements in an IObservableList < Integer >.

 final IObservableList addends = WritableValue.withValueType(Integer.TYPE);
 addends.add(new Integer(0));
 addends.add(new Integer(1));
 addends.add(new Integer(2));
 
 IObservableValue sum = new ComputedValue() {
        protected Object calculate() {
                int sum = 0;
                for (Iterator it = addends.iterator(); it.hasNext();) {
                        Integer addend = (Integer) it.next();
                        sum += addend.intValue();
                }
                return sum;
        }
 };
 
 System.out.println(sum.getValue()); // => 3
 
 addends.add(new Integer(10));
 System.out.println(sum.getValue()); // => 13
 

Since:

1.0

Constructor Summary
ComputedValue ()
ComputedValue ( Object valueType)
ComputedValue ( Realm realm)
ComputedValue ( Realm realm, Object valueType)

 

Method Summary
void	addChangeListener ( IChangeListener listener)           Adds the given change listener to the list of change listeners.
protected  void	addListener ( Object listenerType, IObservablesListener listener)
void	addValueChangeListener ( IValueChangeListener listener)
protected abstract   Object	calculate ()           Subclasses must override this method to provide the object's value.
protected   Object	clone ()
void	dispose ()           Disposes of this observable object, removing all listeners registered with this object, and all listeners this object might have registered on other objects.
protected   Object	doGetValue ()
protected  void	fireEvent ( ObservableEvent event)
protected  void	firstListenerAdded ()
Realm	getRealm ()
Object	getValueType ()           The value type of this observable value, or null if this observable value is untyped.
protected  boolean	hasListeners ()
boolean	isStale ()           Returns whether the state of this observable is stale and is expected to change soon.
protected  void	lastListenerRemoved ()
protected  void	makeDirty ()
protected  void	removeListener ( Object listenerType, IObservablesListener listener)

 

Methods inherited from class org.eclipse.core.databinding.observable.value. AbstractObservableValue
doSetValue, fireChange, fireValueChange, getValue, removeValueChangeListener, setValue

 

Methods inherited from class org.eclipse.core.databinding.observable. AbstractObservable
addDisposeListener, addStaleListener, checkRealm, fireStale, isDisposed, removeChangeListener, removeDisposeListener, removeStaleListener

 

Methods inherited from class java.lang. Object
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Methods inherited from interface org.eclipse.core.databinding.observable. IObservable
addDisposeListener, addStaleListener, getRealm, isDisposed, removeChangeListener, removeDisposeListener, removeStaleListener

 

Constructor Detail

ComputedValue

public ComputedValue()

ComputedValue

public ComputedValue(
Object valueType)

Parameters:

valueType - can be null

ComputedValue

public ComputedValue(
Realm realm)

Parameters:

realm -

ComputedValue

public ComputedValue(
Realm realm,
                     
Object valueType)

Parameters:

realm -

valueType -

doGetValue

protected final 
Object doGetValue()

Specified by:

doGetValue in class AbstractObservableValue

calculate

protected abstract 
Object calculate()

Subclasses must override this method to provide the object's value. Any dependencies used to calculate the value must be IObservable, and implementers must use one of the interface methods tagged TrackedGetter for ComputedValue to recognize it as a dependency.

Returns:

the object's value

makeDirty

protected final void makeDirty()

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 AbstractObservableValue

Returns:

true if this observable's state is stale and will change soon.

getValueType

public 
Object getValueType()

Description copied from interface: IObservableValue

The value type of this observable value, or null if this observable value is untyped.

Returns:

the value type, or null

protected boolean hasListeners()

public void addChangeListener(
IChangeListener listener)

public void addValueChangeListener(
IValueChangeListener listener)

public void dispose()

protected void addListener(
Object listenerType,
                           
IObservablesListener listener)

protected void removeListener(
Object listenerType,
                              
IObservablesListener listener)

protected void fireEvent(
ObservableEvent event)

protected void firstListenerAdded()

protected void lastListenerRemoved()

public 
Realm getRealm()

protected 
Object clone()
                throws 
CloneNotSupportedException