[201159] model rework

1 files changed, 64 insertions, 0 deletions

diff --git a/jpa/plugins/org.eclipse.jpt.utility/src/org/eclipse/jpt/utility/internal/model/value/NullPropertyValueModel.java b/jpa/plugins/org.eclipse.jpt.utility/src/org/eclipse/jpt/utility/internal/model/value/NullPropertyValueModel.java
new file mode 100644
index 0000000000..ebd80c1da3
--- /dev/null
+++ b/jpa/plugins/org.eclipse.jpt.utility/src/org/eclipse/jpt/utility/internal/model/value/NullPropertyValueModel.java
@@ -0,0 +1,64 @@
+/*******************************************************************************
+ * Copyright (c) 2007 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.utility.internal.model.value;
+
+/**
+ * A read-only property value model for when you
+ * don't need to support a value.
+ */
+public final class NullPropertyValueModel
+	extends AbstractReadOnlyPropertyValueModel
+{
+
+	private static final long serialVersionUID = 1L;
+
+	// singleton
+	private static NullPropertyValueModel INSTANCE;
+
+	/**
+	 * Return the singleton.
+	 */
+	public static synchronized PropertyValueModel instance() {
+		if (INSTANCE == null) {
+			INSTANCE = new NullPropertyValueModel();
+		}
+		return INSTANCE;
+	}
+
+	/**
+	 * Ensure non-instantiability.
+	 */
+	private NullPropertyValueModel() {
+		super();
+	}
+	
+
+	// ********** PropertyValueModel implementation **********
+
+	public Object getValue() {
+		return null;
+	}
+
+
+	// ********** Object overrides **********
+
+    @Override
+	public String toString() {
+		return "NullPropertyValueModel";
+	}
+
+	/**
+	 * Serializable singleton support
+	 */
+	private Object readResolve() {
+		return instance();
+	}
+
+}