diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/OptimizationClassBuilder.java b/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/OptimizationClassBuilder.java
deleted file mode 100644
index 260166ca980..00000000000
--- a/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/OptimizationClassBuilder.java
+++ /dev/null
@@ -1,57 +0,0 @@
-/*
- * Copyright 2010-2015 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.codegen.optimization;
-
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
-import org.jetbrains.kotlin.codegen.ClassBuilder;
-import org.jetbrains.kotlin.codegen.DelegatingClassBuilder;
-import org.jetbrains.kotlin.codegen.state.GenerationState;
-import org.jetbrains.kotlin.resolve.jvm.diagnostics.JvmDeclarationOrigin;
-import org.jetbrains.org.objectweb.asm.MethodVisitor;
-
-public class OptimizationClassBuilder extends DelegatingClassBuilder {
-    private final ClassBuilder delegate;
-    private final GenerationState generationState;
-
-    public OptimizationClassBuilder(@NotNull ClassBuilder delegate, @NotNull GenerationState generationState) {
-        this.delegate = delegate;
-        this.generationState = generationState;
-    }
-
-    @NotNull
-    @Override
-    public ClassBuilder getDelegate() {
-        return delegate;
-    }
-
-    @NotNull
-    @Override
-    public MethodVisitor newMethod(
-            @NotNull JvmDeclarationOrigin origin,
-            int access,
-            @NotNull String name,
-            @NotNull String desc,
-            @Nullable String signature,
-            @Nullable String[] exceptions
-    ) {
-        return new OptimizationMethodVisitor(
-                super.newMethod(origin, access, name, desc, signature, exceptions),
-                generationState, access, name, desc, signature, exceptions
-        );
-    }
-}
diff --git a/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/OptimizationClassBuilder.kt b/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/OptimizationClassBuilder.kt
new file mode 100644
index 00000000000..d023a57e191
--- /dev/null
+++ b/compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/OptimizationClassBuilder.kt
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jetbrains.kotlin.codegen.optimization
+
+import org.jetbrains.kotlin.codegen.ClassBuilder
+import org.jetbrains.kotlin.codegen.DelegatingClassBuilder
+import org.jetbrains.kotlin.codegen.state.GenerationState
+import org.jetbrains.kotlin.resolve.jvm.diagnostics.JvmDeclarationOrigin
+import org.jetbrains.org.objectweb.asm.MethodVisitor
+
+class OptimizationClassBuilder(private val delegate: ClassBuilder, private val generationState: GenerationState) :
+    DelegatingClassBuilder() {
+
+    public override fun getDelegate(): ClassBuilder = delegate
+
+    override fun newMethod(
+        origin: JvmDeclarationOrigin,
+        access: Int,
+        name: String,
+        desc: String,
+        signature: String?,
+        exceptions: Array<String>?
+    ): MethodVisitor {
+        return OptimizationMethodVisitor(
+            super.newMethod(origin, access, name, desc, signature, exceptions),
+            generationState, access, name, desc, signature, exceptions
+        )
+    }
+}
\ No newline at end of file