Index: settings/build-properties.xml
===================================================================
--- settings/build-properties.xml	(revision 29007)
+++ settings/build-properties.xml	(working copy)
@@ -31,4 +31,7 @@
     <property name="run-module-manager" value="false"/>
     <property name="url" value="undefined"/>
     <property name="number" value="undefined"/>
+    <property name="depend" value="false" />
+    <property name="depend-classpath" value="false" />
+    <property name="depend-closure" value="false" />
 </project>
Index: src/org/kepler/build/CompileModules.java
===================================================================
--- src/org/kepler/build/CompileModules.java	(revision 29007)
+++ src/org/kepler/build/CompileModules.java	(working copy)
@@ -26,6 +26,8 @@
 package org.kepler.build;
 
 import org.apache.tools.ant.taskdefs.Javac;
+import org.apache.tools.ant.taskdefs.optional.depend.Depend;
+import org.apache.tools.ant.types.Path;
 import org.kepler.build.modules.Module;
 import org.kepler.build.modules.ModulesTask;
 import org.kepler.build.project.CompileClasspath;
@@ -51,6 +53,9 @@
     protected String moduleName = "undefined";
     protected String compilerArgs = "undefined";
     protected boolean debug = false;
+    protected boolean depend = false;
+    protected boolean dependClasspath = false;
+    protected boolean dependClosure = false;
     protected List<String> exclude = new ArrayList<String>();
     protected List<String> include = new ArrayList<String>();
 
@@ -85,6 +90,36 @@
     }
 
     /**
+     * set whether to use java dependencies to delete out of date files
+     *
+     * @param depend
+     */
+    public void setDepend(boolean depend)
+    {
+        this.depend = depend;
+    }
+
+    /**
+     * set whether Depend should use the classpath
+     *
+     * @param dependClasspath
+     */
+    public void setDependClasspath(boolean dependClasspath)
+    {
+        this.dependClasspath = dependClasspath;
+    }
+
+    /**
+     * set whether Depend should use closure
+     *
+     * @param dependClosure
+     */
+    public void setDependClosure(boolean dependClosure)
+    {
+        this.dependClosure = dependClosure;
+    }
+
+    /**
      * set any includes
      *
      * @param include
@@ -230,18 +265,76 @@
         javac.setFork(true);
         javac.setMemoryMaximumSize("512m");
         javac.setFailonerror(true);
+
+        // Depend helps Javac by deleting out of date class files by
+        // determining dependencies rather than just timestamps.
+        Depend dep = null;
+        if (this.depend) {
+            dep = new Depend();
+            dep.bindToOwner(this);
+            dep.setSrcdir(module.getSrcPath());
+
+            if (this.dependClasspath) {
+                // Ant assumes that anything in the path that's not a directory
+                // is a jar.  Kepler adds a lot of non-jar files to the
+                // classpath including *.htm and *.in.  If you don't filter them
+                // out of the classpath for Depend, it will throw an exception.
+                Path cleanClasspath = new Path(classpath.getProject());
+                for (String s : classpath.list()) {
+                    if (s.toLowerCase().endsWith(".jar") || new File(s).isDirectory()) {
+                        cleanClasspath.setPath(s);
+                    }
+                }
+            } else {
+                dep.createClasspath();
+            }
+
+            Path path = new Path(module.getSrcPath().getProject(), classes.getAbsolutePath());
+            dep.setDestDir(path);
+            dep.setWarnOnRmiStubs(true);
+    
+            if (this.dependClosure) {
+                dep.setClosure(false);
+            }
+        }
+
         if (osDependentExcludes)
         {
             javac.setExcludesfile(new File(basedir, "build-area/settings/os-dependent-excludes"));
+
+            if (this.depend) {
+                dep.setExcludesfile(new File(basedir, "build-area/settings/os-dependent-excludes"));
+            }
         }
 
         if (mn.equals(Module.PTOLEMY) || mn.matches(Module.PTOLEMY+"-\\d+\\.\\d+") || 
         		mn.matches(Module.PTOLEMY_KEPLER+"-\\d+\\.\\d+"))
         {
             javac.setIncludesfile(new File(basedir, "build-area/settings/ptolemy-includes"));
+            if (this.depend) {
+                dep.setIncludesfile(new File(basedir, "build-area/settings/ptolemy-includes"));
+            }
+
             javac.setExcludesfile(new File(basedir, "build-area/settings/ptolemy-excludes"));
+            if (this.depend) {
+                dep.setExcludesfile(new File(basedir, "build-area/settings/ptolemy-excludes"));
+            }
         }
 
+        if (this.depend) {
+            File baseCache = new File("./depcache");
+            if (! baseCache.exists()) {
+                baseCache.mkdirs();
+            }
+    
+            // Depend uses this path.  In practice, it will create
+            // ./depcache/<modulename>/dependencies.txt
+            File modDep = new File(baseCache, module.toString());
+            dep.setCache(modDep);
+    
+            dep.execute();
+        }
+
         if (!compilerArgs.equals("undefined"))
         {
             String[] args = compilerArgs.split(",");
Index: build.xml
===================================================================
--- build.xml	(revision 29007)
+++ build.xml	(working copy)
@@ -45,7 +45,7 @@
 
 	<target name="compile" description="Compile all the modules in modules.txt.">
 	        <echo>Note that you may need to run "ant force-ptolemy compile" to compile ptolemy.</echo>
-		<compile module="${module}" compilerArgs="${compiler-args}" debug="${debug}" include="${include}" exclude="${exclude}" skip="${skip}" />
+		<compile module="${module}" compilerArgs="${compiler-args}" debug="${debug}" include="${include}" exclude="${exclude}" skip="${skip}" depend="${depend}" dependClasspath="${depend-classpath}" dependClosure="${depend-closure}" />
 	</target>
 
 	<target name="run" depends="compile" description="Compile, then run Kepler along with the modules in modules.txt.  Use -Dworkflow=model.xml to run a model.">