add PredicatePropertyValueModel

1 files changed, 108 insertions, 0 deletions

diff --git a/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/model/value/PredicatePropertyValueModel.java b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/model/value/PredicatePropertyValueModel.java
new file mode 100644
index 0000000000..5bd38b2af6
--- /dev/null
+++ b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/model/value/PredicatePropertyValueModel.java
@@ -0,0 +1,108 @@
+/*******************************************************************************
+ * Copyright (c) 2013 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.model.value.PropertyValueModel;
+import org.eclipse.jpt.common.utility.predicate.Predicate;
+
+/**
+ * A <code>PredicatePropertyValueModel</code> wraps another
+ * {@link PropertyValueModel} and uses a {@link Predicate}
+ * to evaluate the wrapped value before it is returned by {@link #getValue()}.
+ * <p>
+ * The evaluated value is calculated and cached during initialization and every
+ * time the wrapped value changes. This can be useful when the old value
+ * passed in to {@link #wrappedValueChanged(org.eclipse.jpt.common.utility.model.event.PropertyChangeEvent)}
+ * can no longer be "evaluated" because its state is no longer valid.
+ * This caching can also improve time performance in some situations.
+ * 
+ * @param <V> the type of the <em>wrapped</em> model's value
+ * @see Predicate
+ */
+public class PredicatePropertyValueModel<V>
+	extends PropertyValueModelWrapper<V>
+	implements PropertyValueModel<Boolean>
+{
+	/**
+	 * Cache the predicate value so that during property change event
+	 * notification we do not have to evaluate the old value. It is possible
+	 * the old value is no longer be valid in the model; as a result,
+	 * evaluating it would not be valid.
+	 */
+	protected volatile Boolean value;
+
+	protected final Predicate<? super V> predicate;
+
+
+	// ********** constructors/initialization **********
+
+	/**
+	 * Construct a property value model with the specified nested
+	 * property value model and predicate. Depending on the nested model,
+	 * the transformer may be required to handle a <code>null</code> value.
+	 */
+	public PredicatePropertyValueModel(PropertyValueModel<? extends V> valueModel, Predicate<? super V> predicate) {
+		super(valueModel);
+		if (predicate == null) {
+			throw new NullPointerException();
+		}
+		this.predicate = predicate;
+	}
+
+	/**
+	 * No need to evaluate the nested value, simply return the cached value,
+	 * which is already evaluated.
+	 */
+	public Boolean getValue() {
+		return this.value;
+	}
+
+	/**
+	 * Propagate the event with transformed values.
+	 */
+	@Override
+	protected void wrappedValueChanged(V oldValue, V newValue) {
+		Boolean old = this.value;
+		this.firePropertyChanged(VALUE, old, this.value = this.evaluate(newValue));
+	}
+
+
+	// ********** transformation **********
+
+	/**
+	 * Evaluate the specified value and return the result.
+	 */
+	protected Boolean evaluate(V v) {
+		return Boolean.valueOf(this.predicate.evaluate(v));
+	}
+
+	/**
+	 * We have listeners, transform the nested value and cache the result.
+	 */
+	@Override
+	protected void engageModel() {
+		super.engageModel();
+		this.value = this.evaluate(this.valueModel.getValue());
+	}
+
+	/**
+	 * We have no more listeners, clear the cached value.
+	 */
+	@Override
+	protected void disengageModel() {
+		this.value = null;
+		super.disengageModel();
+	}
+
+	@Override
+	public void toString(StringBuilder sb) {
+		sb.append(this.value);
+	}
+}