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git-svn-id: file:///usr/local/projects/SUN/JOGL/git-svn/svn-server-sync/joglutils/trunk@46 83d24430-9974-4f80-8418-2cc3294053b9

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diff --git a/src/net/java/joglutils/msg/misc/ActionTable.java b/src/net/java/joglutils/msg/misc/ActionTable.java
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+/*
+ * Copyright (c) 2007 Sun Microsystems, Inc. All Rights Reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 
+ * - Redistribution of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * 
+ * - Redistribution in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * 
+ * Neither the name of Sun Microsystems, Inc. or the names of
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ * 
+ * This software is provided "AS IS," without a warranty of any kind. ALL
+ * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES,
+ * INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A
+ * PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN
+ * MICROSYSTEMS, INC. ("SUN") AND ITS LICENSORS SHALL NOT BE LIABLE FOR
+ * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
+ * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR
+ * ITS LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR
+ * DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE
+ * DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY,
+ * ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE, EVEN IF
+ * SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
+ * 
+ * You acknowledge that this software is not designed or intended for use
+ * in the design, construction, operation or maintenance of any nuclear
+ * facility.
+ * 
+ */
+
+package net.java.joglutils.msg.misc;
+
+import java.lang.reflect.*;
+import java.util.*;
+
+import net.java.joglutils.msg.actions.*;
+import net.java.joglutils.msg.nodes.*;
+
+/** Keeps track of methods which are attached to a particular Action
+    type for a given set of Node types. This mechanism is different
+    than using the typical Visitor design pattern because Actions,
+    even built-in Actions, need to easily support the addition of
+    newly added Node types. Dispatch occurs via reflection on a
+    per-Node-type basis. */
+
+public class ActionTable {
+  private Class<? extends Action> actionClass;
+  private Map<Class<? extends Node>, Method> methodMap = new HashMap<Class<? extends Node>, Method>();
+
+  /** Creates an ActionTable intended for use with a particular Action
+      subclass. */
+  public ActionTable(Class<? extends Action> actionClass) {
+    this.actionClass = actionClass;
+  }
+
+  /** Adds an action method for a particular node type to this
+      table. This method will apply to this type and all subtypes
+      unless one is added for a more specific subtype. An action
+      method is defined as a public static method with the following
+      signature: <P>
+
+      <CODE>public static void [method name]([Action subclass] action, [Node subclass] node)</CODE> <P>
+
+      The action subclass may be the action class this ActionTable was
+      created with, or any supertype up to and including the Action
+      class. This avoids unnecessary downcasting of the Action in
+      action methods. <P>
+
+      The node subclass may be the node type which is passed in to the
+      addActionMethod call, or any supertype up to and including the
+      Node class. This allows convenient overloading of action
+      methods. <P>
+
+      Note that it does not matter which type the action method is
+      attached to. This is a key mechanism for extensibility; new
+      action methods can be attached to existing action types to
+      handle new node types which are added to the system. <P>
+
+      An action uses reflection to dispatch to these methods at run
+      time, caching lookup results for node types which have not been
+      encountered yet.
+  */
+  public void addActionMethod(Class<? extends Node> nodeType, Method actionMethod)
+    throws IllegalArgumentException
+  {
+    // Check the method to see whether it obeys our properties
+    if (!Modifier.isPublic(actionMethod.getModifiers())) {
+      throw new IllegalArgumentException("Action method must be public");
+    }
+    if (!Modifier.isStatic(actionMethod.getModifiers())) {
+      throw new IllegalArgumentException("Action method must be static");
+    }
+    Class<?>[] argTypes = actionMethod.getParameterTypes();
+    if (argTypes.length != 2) {
+      throw new IllegalArgumentException("Action method must take 2 arguments");
+    }
+    if (!argTypes[0].isAssignableFrom(actionClass)) {
+      throw new IllegalArgumentException("Action method must take a " + actionClass +
+                                         " or superclass as its first argument");
+    }
+    if (!argTypes[1].isAssignableFrom(nodeType)) {
+      throw new IllegalArgumentException("Action method must take a " + nodeType +
+                                         " or superclass as its second argument");
+    }
+    methodMap.put(nodeType, actionMethod);
+  }
+
+  /** Looks up the appropriate action method for the given node.
+      Performs caching internally to avoid excessive reflective
+      lookups. Returns null if no action method was registered. This
+      should only happen if an action method was not registered for
+      the base Node type. */
+  public Method lookupActionMethod(Node node) {
+    Class<? extends Node> nodeType = node.getClass();
+    Class<? extends Node> curType = nodeType;
+    do {
+      Method m = methodMap.get(curType);
+      if (m != null) {
+        // See whether we need to cache this result
+        if (curType != nodeType) {
+          methodMap.put(curType, m);
+        }
+        return m;
+      }
+      Class<?> nextType = curType.getSuperclass();
+      if (Node.class.isAssignableFrom(nextType)) {
+        curType = (Class<? extends Node>) nextType;
+      } else {
+        curType = null;
+      }
+    } while (curType != null);
+    return null;
+  }
+}