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diff --git a/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/model/value/ValueAspectAdapter.java b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/model/value/ValueAspectAdapter.java
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+++ b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/model/value/ValueAspectAdapter.java
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+/*******************************************************************************
+ * Copyright (c) 2007, 2009 Oracle. All rights reserved.
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0, which accompanies this distribution
+ * and is available at http://www.eclipse.org/legal/epl-v10.html.
+ * 
+ * Contributors:
+ *     Oracle - initial API and implementation
+ ******************************************************************************/
+package org.eclipse.jpt.common.utility.internal.model.value;
+
+import org.eclipse.jpt.common.utility.internal.model.ChangeSupport;
+import org.eclipse.jpt.common.utility.model.event.PropertyChangeEvent;
+import org.eclipse.jpt.common.utility.model.listener.StateChangeListener;
+import org.eclipse.jpt.common.utility.model.value.WritablePropertyValueModel;
+
+/**
+ * Abstract class that provides support for wrapping a {@link WritablePropertyValueModel}
+ * and listening for changes to <em>aspects</em> of the <em>value</em> contained
+ * by the {@link WritablePropertyValueModel}. Changes to the {@link WritablePropertyValueModel}'s
+ * value are also monitored.
+ * <p>
+ * This is useful if you have a value that may change, but whose aspects can also
+ * change in a fashion that might be of interest to the client.
+ * <p>
+ * <strong>NB:</strong> Clients will need to listen for two different change notifications:
+ * a property change event will be be fired when the <em>value</em> changes;
+ * a state change event will be fired when an <em>aspect</em> of the value changes.
+ * <p>
+ * Subclasses need to override two methods:<ul>
+ * <li>{@link #engageValue_()}<p>
+ *     begin listening to the appropriate aspect of the value and call
+ *     {@link #valueAspectChanged()} whenever the aspect changes
+ *     (this will fire a state change event)
+ * <li>{@link #disengageValue_()}<p>
+ *     stop listening to the appropriate aspect of the value
+ * </ul>
+ */
+public abstract class ValueAspectAdapter<V>
+	extends PropertyValueModelWrapper<V>
+	implements WritablePropertyValueModel<V>
+{
+	/** Cache the value so we can disengage. Null until we have a listener*/
+	protected V value;
+
+
+	// ********** constructors/initialization **********
+
+	/**
+	 * Constructor - the value holder is required.
+	 */
+	protected ValueAspectAdapter(WritablePropertyValueModel<V> valueHolder) {
+		super(valueHolder);
+		this.value = null;
+	}
+
+	/**
+	 * Override to allow both property and state change listeners.
+	 */
+	@Override
+	protected ChangeSupport buildChangeSupport() {
+		return new ChangeSupport(this);
+	}
+
+
+	// ********** PropertyValueModel implementation **********
+
+	public V getValue() {
+		return this.value;
+	}
+
+
+	// ********** WritablePropertyValueModel implementation **********
+
+	public void setValue(V value) {
+		this.getValueHolder().setValue(value);
+	}
+
+
+	// ********** PropertyValueModelWrapper implementation **********
+
+	@Override
+	protected void valueChanged(PropertyChangeEvent event) {
+		this.disengageValue();
+		this.engageValue();
+		this.firePropertyChanged(event.clone(this));
+	}
+
+
+	// ********** extend change support **********
+
+	/**
+	 * Extend to start listening to the underlying model if necessary.
+	 */
+	@Override
+	public synchronized void addStateChangeListener(StateChangeListener listener) {
+		if (this.hasNoListeners()) {
+			this.engageModel();
+		}
+		super.addStateChangeListener(listener);
+	}
+
+	/**
+	 * Extend to stop listening to the underlying model if necessary.
+	 */
+	@Override
+	public synchronized void removeStateChangeListener(StateChangeListener listener) {
+		super.removeStateChangeListener(listener);
+		if (this.hasNoListeners()) {
+			this.disengageModel();
+		}
+	}
+
+
+	// ********** AbstractPropertyValueModel overrides **********
+
+	/**
+	 * Extend to check for state change listeners.
+	 */
+	@Override
+	protected boolean hasListeners() {
+		return this.hasAnyStateChangeListeners() || super.hasListeners();
+	}
+
+
+	// ********** PropertyValueModelWrapper overrides **********
+
+	/**
+	 * Extend to engage an aspect of the value model's value.
+	 */
+	@Override
+	protected void engageModel() {
+		super.engageModel();
+		this.engageValue();
+	}
+
+	/**
+	 * Extend to disengage an aspect of the value model's value.
+	 */
+	@Override
+	protected void disengageModel() {
+		this.disengageValue();
+		super.disengageModel();
+	}
+
+
+	// ********** behavior **********
+
+	/**
+	 * Start listening to an aspect of the current value.
+	 */
+	protected void engageValue() {
+		this.value = this.valueHolder.getValue();
+		if (this.value != null) {
+			this.engageValue_();
+		}
+	}
+
+	/**
+	 * Start listening to some aspect of the current value.
+	 * At this point we can be sure the value is not null.
+	 */
+	protected abstract void engageValue_();
+
+	/**
+	 * Stop listening to an aspect of the current value.
+	 */
+	protected void disengageValue() {
+		if (this.value != null) {
+			this.disengageValue_();
+			this.value = null;
+		}
+	}
+
+	/**
+	 * Stop listening to an aspect of the current value.
+	 * At this point we can be sure the value is not null.
+	 */
+	protected abstract void disengageValue_();
+
+	/**
+	 * Subclasses should call this method whenever the value's aspect changes.
+	 */
+	protected void valueAspectChanged() {
+		this.fireStateChanged();
+	}
+
+	/**
+	 * Our constructor accepts only a {@link WritablePropertyValueModel}{@code<V>}.
+	 */
+	@SuppressWarnings("unchecked")
+	protected WritablePropertyValueModel<V> getValueHolder() {
+		return (WritablePropertyValueModel<V>) this.valueHolder;
+	}
+
+	@Override
+	public void toString(StringBuilder sb) {
+		sb.append(this.getValue());
+	}
+
+}