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diff --git a/server/src/com/vaadin/data/Collapsible.java b/server/src/com/vaadin/data/Collapsible.java
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+/*
+@VaadinApache2LicenseForJavaFiles@
+ */
+package com.vaadin.data;
+
+import com.vaadin.data.Container.Hierarchical;
+import com.vaadin.data.Container.Ordered;
+
+/**
+ * Container needed by large lazy loading hierarchies displayed e.g. in
+ * TreeTable.
+ * <p>
+ * Container of this type gets notified when a subtree is opened/closed in a
+ * component displaying its content. This allows container to lazy load subtrees
+ * and release memory when a sub-tree is no longer displayed.
+ * <p>
+ * Methods from {@link Container.Ordered} (and from {@linkContainer.Indexed} if
+ * implemented) are expected to work as in "preorder" of the currently visible
+ * hierarchy. This means for example that the return value of size method
+ * changes when subtree is collapsed/expanded. In other words items in collapsed
+ * sub trees should be "ignored" by container when the container is accessed
+ * with methods introduced in {@link Container.Ordered} or
+ * {@linkContainer.Indexed}. From the accessors point of view, items in
+ * collapsed subtrees don't exist.
+ * <p>
+ * 
+ */
+public interface Collapsible extends Hierarchical, Ordered {
+
+    /**
+     * <p>
+     * Collapsing the {@link Item} indicated by <code>itemId</code> hides all
+     * children, and their respective children, from the {@link Container}.
+     * </p>
+     * 
+     * <p>
+     * If called on a leaf {@link Item}, this method does nothing.
+     * </p>
+     * 
+     * @param itemId
+     *            the identifier of the collapsed {@link Item}
+     * @param collapsed
+     *            <code>true</code> if you want to collapse the children below
+     *            this {@link Item}. <code>false</code> if you want to
+     *            uncollapse the children.
+     */
+    public void setCollapsed(Object itemId, boolean collapsed);
+
+    /**
+     * <p>
+     * Checks whether the {@link Item}, identified by <code>itemId</code> is
+     * collapsed or not.
+     * </p>
+     * 
+     * <p>
+     * If an {@link Item} is "collapsed" its children are not included in
+     * methods used to list Items in this container.
+     * </p>
+     * 
+     * @param itemId
+     *            The {@link Item}'s identifier that is to be checked.
+     * @return <code>true</code> iff the {@link Item} identified by
+     *         <code>itemId</code> is currently collapsed, otherwise
+     *         <code>false</code>.
+     */
+    public boolean isCollapsed(Object itemId);
+
+}