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diff --git a/bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/widgets/Layout.java b/bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/widgets/Layout.java
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+/*******************************************************************************
+ * Copyright (c) 2000, 2008 IBM Corporation and others.
+ * 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:
+ *     IBM Corporation - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.swt.widgets;
+
+
+import org.eclipse.swt.graphics.*;
+
+/**
+ * A layout controls the position and size
+ * of the children of a composite widget.
+ * This class is the abstract base class for
+ * layouts.
+ * 
+ * @see Composite#setLayout(Layout)
+ * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
+ */
+public abstract class Layout {
+
+/**
+ * Computes and returns the size of the specified
+ * composite's client area according to this layout.
+ * <p>
+ * This method computes the size that the client area 
+ * of the composite must be in order to position all 
+ * children at their preferred size inside the
+ * composite according to the layout algorithm
+ * encoded by this layout.
+ * </p>
+ * <p>
+ * When a width or height hint is supplied, it is
+ * used to constrain the result. For example, if a
+ * width hint is provided that is less than the
+ * width of the client area, the layout may choose
+ * to wrap and increase height, clip, overlap, or
+ * otherwise constrain the children.
+ * </p>
+ *
+ * @param composite a composite widget using this layout
+ * @param wHint width (<code>SWT.DEFAULT</code> for preferred size)
+ * @param hHint height (<code>SWT.DEFAULT</code> for preferred size)
+ * @param flushCache <code>true</code> means flush cached layout values
+ * @return a point containing the computed size (width, height)
+ * 
+ * @see #layout
+ * @see Control#getBorderWidth
+ * @see Control#getBounds
+ * @see Control#getSize
+ * @see Control#pack(boolean)
+ * @see "computeTrim, getClientArea for controls that implement them"
+ */
+protected abstract Point computeSize (Composite composite, int wHint, int hHint, boolean flushCache);
+
+/**
+ * Instruct the layout to flush any cached values
+ * associated with the control specified in the argument 
+ * <code>control</code>.
+ * 
+ * @param control a control managed by this layout
+ * @return true if the Layout has flushed all cached information associated with control
+ * 
+ * @since 3.1
+ */
+protected boolean flushCache (Control control) {
+	return false;
+}
+
+/**
+ * Lays out the children of the specified composite
+ * according to this layout.
+ * <p>
+ * This method positions and sizes the children of a
+ * composite using the layout algorithm encoded by this
+ * layout. Children of the composite are positioned in
+ * the client area of the composite. The position of
+ * the composite is not altered by this method.
+ * </p>
+ * <p>
+ * When the flush cache hint is true, the layout is
+ * instructed to flush any cached values associated
+ * with the children. Typically, a layout will cache
+ * the preferred sizes of the children to avoid the
+ * expense of computing these values each time the
+ * widget is laid out.
+ * </p>
+ * <p>
+ * When layout is triggered explicitly by the programmer
+ * the flush cache hint is true. When layout is triggered
+ * by a resize, either caused by the programmer or by the
+ * user, the hint is false.
+ * </p>
+ *
+ * @param composite a composite widget using this layout
+ * @param flushCache <code>true</code> means flush cached layout values
+ */
+protected abstract void layout (Composite composite, boolean flushCache);
+}