diff --git a/ganttzk/src/main/java/org/zkoss/ganttz/adapters/State.java b/ganttzk/src/main/java/org/zkoss/ganttz/adapters/State.java
new file mode 100644
index 000000000..c4bedd7db
--- /dev/null
+++ b/ganttzk/src/main/java/org/zkoss/ganttz/adapters/State.java
@@ -0,0 +1,83 @@
+/*
+ * This file is part of ###PROJECT_NAME###
+ *
+ * Copyright (C) 2009 Fundación para o Fomento da Calidade Industrial e
+ *                    Desenvolvemento Tecnolóxico de Galicia
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.zkoss.ganttz.adapters;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Represents a value that can be changed. It notifies the interested
+ * {@link IValueChangeListener listeners} when the value is changed
+ * @author Óscar González Fernández <ogonzalez@igalia.com>
+ */
+public class State<T> {
+
+    public interface IValueChangeListener<T> {
+        public void hasChanged(State<T> state);
+    }
+
+    public static <T> State<T> create(T value) {
+        return new State<T>(value);
+    }
+
+    public static State<Void> create() {
+        return new State<Void>();
+    }
+
+    private List<IValueChangeListener<T>> listeners = new ArrayList<IValueChangeListener<T>>();
+    private T value;
+    private boolean isVoid = false;
+
+    private State(T value) {
+        this.value = value;
+    }
+
+    private State() {
+        this.value = null;
+        isVoid = true;
+    }
+
+    public T getValue() {
+        return value;
+    }
+
+    public void changeValueTo(T value) {
+        if (!isVoid && this.value == value) {
+            return;
+        }
+        this.value = value;
+        fireChange();
+    }
+
+    private void fireChange() {
+        for (IValueChangeListener<T> listener : listeners) {
+            listener.hasChanged(this);
+        }
+    }
+
+    public void addListener(IValueChangeListener<T> listener) {
+        listeners.add(listener);
+    }
+
+    public void removeListener(IValueChangeListener<?> listener) {
+        listeners.remove(listener);
+    }
+
+}