diff --git a/idea/src/META-INF/plugin.xml b/idea/src/META-INF/plugin.xml
index 1d83d95d8bc..6fd690eba51 100644
--- a/idea/src/META-INF/plugin.xml
+++ b/idea/src/META-INF/plugin.xml
@@ -59,7 +59,9 @@
       <codeInsight.overrideMethod language="jet" implementationClass="org.jetbrains.jet.plugin.codeInsight.OverrideMethodsHandler"/>
 
 
-      <!--<java.elementFinder implementation="org.jetbrains.jet.plugin.java.JavaElementFinder"/>-->
+      <java.elementFinder implementation="org.jetbrains.jet.plugin.java.JavaElementFinder"/>
+      <psi.treeChangePreprocessor implementation="org.jetbrains.jet.plugin.java.JetCodeBlockModificationListener"/>
+
       <toolWindow id="CodeWindow"
                   factoryClass="org.jetbrains.jet.plugin.internal.codewindow.BytecodeToolwindow$Factory"
                   anchor="right"/>
diff --git a/idea/src/org/jetbrains/jet/plugin/java/JetCodeBlockModificationListener.java b/idea/src/org/jetbrains/jet/plugin/java/JetCodeBlockModificationListener.java
new file mode 100644
index 00000000000..dd26ab448c4
--- /dev/null
+++ b/idea/src/org/jetbrains/jet/plugin/java/JetCodeBlockModificationListener.java
@@ -0,0 +1,112 @@
+/*
+ * @author max
+ */
+package org.jetbrains.jet.plugin.java;
+
+import com.intellij.openapi.diagnostic.Logger;
+import com.intellij.psi.*;
+import com.intellij.psi.impl.PsiModificationTrackerImpl;
+import com.intellij.psi.impl.PsiTreeChangeEventImpl;
+import com.intellij.psi.impl.PsiTreeChangePreprocessor;
+import com.intellij.psi.util.PsiModificationTracker;
+import org.jetbrains.jet.lang.psi.JetBlockExpression;
+import org.jetbrains.jet.lang.psi.JetClass;
+import org.jetbrains.jet.lang.psi.JetFile;
+
+public class JetCodeBlockModificationListener implements PsiTreeChangePreprocessor {
+    private static final Logger LOG = Logger.getInstance("#org.jetbrains.jet.plugin.java.JetCodeBlockModificationListener");
+    
+    private final PsiModificationTrackerImpl myModificationTracker;
+
+    public JetCodeBlockModificationListener(final PsiModificationTracker modificationTracker) {
+        myModificationTracker = (PsiModificationTrackerImpl) modificationTracker;
+    }
+
+    @Override
+    public void treeChanged(final PsiTreeChangeEventImpl event) {
+        switch (event.getCode()) {
+            case BEFORE_CHILDREN_CHANGE:
+            case BEFORE_PROPERTY_CHANGE:
+            case BEFORE_CHILD_MOVEMENT:
+            case BEFORE_CHILD_REPLACEMENT:
+            case BEFORE_CHILD_ADDITION:
+            case BEFORE_CHILD_REMOVAL:
+                break;
+
+            case CHILD_ADDED:
+            case CHILD_REMOVED:
+            case CHILD_REPLACED:
+                processChange(event.getParent(), event.getOldChild(), event.getChild());
+                break;
+
+            case CHILDREN_CHANGED:
+                // general childrenChanged() event after each change
+                if (!event.isGenericChildrenChange()) {
+                    processChange(event.getParent(), event.getParent(), null);
+                }
+                break;
+
+            case CHILD_MOVED:
+            case PROPERTY_CHANGED:
+                myModificationTracker.incCounter();
+                break;
+
+            default:
+                LOG.error("Unknown code:" + event.getCode());
+                break;
+        }
+    }
+
+    private void processChange(final PsiElement parent, final PsiElement child1, final PsiElement child2) {
+        try {
+            if (!isInsideCodeBlock(parent)) {
+                if (parent != null && parent.getContainingFile() instanceof JetFile) {
+                    myModificationTracker.incCounter();
+                }
+                else {
+                    myModificationTracker.incOutOfCodeBlockModificationCounter();
+                }
+                return;
+            }
+
+            if (containsClassesInside(child1) || child2 != child1 && containsClassesInside(child2)) {
+                myModificationTracker.incCounter();
+            }
+        } catch (PsiInvalidElementAccessException e) {
+            myModificationTracker.incCounter(); // Shall not happen actually, just a pre-release paranoia
+        }
+    }
+
+    private static boolean containsClassesInside(final PsiElement element) {
+        if (element == null) return false;
+        if (element instanceof PsiClass) return true;
+
+        PsiElement child = element.getFirstChild();
+        while (child != null) {
+            if (containsClassesInside(child)) return true;
+            child = child.getNextSibling();
+        }
+
+        return false;
+    }
+
+    private static boolean isInsideCodeBlock(PsiElement element) {
+        if (element instanceof PsiFileSystemItem) {
+            return false;
+        }
+
+        if (element == null || element.getParent() == null) return true;
+
+        PsiElement parent = element;
+        while (true) {
+            if (parent instanceof PsiFile || parent instanceof PsiDirectory || parent == null) {
+                return false;
+            }
+            if (parent instanceof JetClass) return false; // anonymous or local class
+            if (parent instanceof JetBlockExpression) {
+                return true;
+            }
+            parent = parent.getParent();
+        }
+    }
+}
diff --git a/idea/src/org/jetbrains/jet/plugin/java/JetLightClass.java b/idea/src/org/jetbrains/jet/plugin/java/JetLightClass.java
index bff50a2487e..3d992837782 100644
--- a/idea/src/org/jetbrains/jet/plugin/java/JetLightClass.java
+++ b/idea/src/org/jetbrains/jet/plugin/java/JetLightClass.java
@@ -15,6 +15,10 @@ import com.intellij.psi.impl.java.stubs.impl.PsiJavaFileStubImpl;
 import com.intellij.psi.impl.light.AbstractLightClass;
 import com.intellij.psi.stubs.PsiClassHolderFileStub;
 import com.intellij.psi.stubs.StubElement;
+import com.intellij.psi.util.CachedValue;
+import com.intellij.psi.util.CachedValueProvider;
+import com.intellij.psi.util.CachedValuesManager;
+import com.intellij.psi.util.PsiModificationTracker;
 import com.intellij.util.containers.Stack;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.jet.codegen.ClassBuilder;
@@ -33,7 +37,7 @@ import java.util.List;
 
 public class JetLightClass extends AbstractLightClass implements JetJavaMirrorMarker {
     private static final Logger LOG = Logger.getInstance("#org.jetbrains.jet.plugin.java.JetLightClass");
-    private final static Key<PsiJavaFileStub> JAVA_API_STUB = Key.create("JAVA_API_STUB");
+    private final static Key<CachedValue<PsiJavaFileStub>> JAVA_API_STUB = Key.create("JAVA_API_STUB");
 
     private final JetFile file;
     private final String className;
@@ -83,13 +87,18 @@ public class JetLightClass extends AbstractLightClass implements JetJavaMirrorMa
     }
 
     private PsiJavaFileStub getStub() {
-        PsiJavaFileStub answer = file.getUserData(JAVA_API_STUB);
+        CachedValue<PsiJavaFileStub> answer = file.getUserData(JAVA_API_STUB);
         if (answer == null) {
-            answer = calcStub();
+            answer = CachedValuesManager.getManager(getProject()).createCachedValue(new CachedValueProvider<PsiJavaFileStub>() {
+                @Override
+                public Result<PsiJavaFileStub> compute() {
+                    return Result.create(calcStub(), PsiModificationTracker.OUT_OF_CODE_BLOCK_MODIFICATION_COUNT);
+                }
+            }, false);
             file.putUserData(JAVA_API_STUB, answer);
         }
         
-        return answer;
+        return answer.getValue();
     }
     
     private PsiJavaFileStub calcStub() {
@@ -139,7 +148,7 @@ public class JetLightClass extends AbstractLightClass implements JetJavaMirrorMa
                 finally {
                     final StubElement pop = stubStack.pop();
                     if (pop != answer) {
-                        LOG.error("Unbalanced stack operations");
+                        LOG.error("Unbalanced stack operations: " + pop);
                     }
                 }
             }