diff --git a/benchmark/src/main/java/org/capnproto/benchmark/CarSales.java b/benchmark/src/main/java/org/capnproto/benchmark/CarSales.java
index 03f25c6..43e6179 100644
--- a/benchmark/src/main/java/org/capnproto/benchmark/CarSales.java
+++ b/benchmark/src/main/java/org/capnproto/benchmark/CarSales.java
@@ -6,7 +6,8 @@ import org.capnproto.Text;
 import org.capnproto.benchmark.CarSalesSchema.*;
 
 public class CarSales
-    implements TestCase<ParkingLot.Builder, ParkingLot.Reader, TotalValue.Builder, TotalValue.Reader, Long> {
+    extends TestCase<ParkingLot.Factory, ParkingLot.Builder, ParkingLot.Reader,
+    TotalValue.Factory, TotalValue.Builder, TotalValue.Reader, Long> {
 
     static final long carValue(Car.Reader car) {
         long result = 0;
@@ -89,7 +90,7 @@ public class CarSales
     }
 
 
-    public Long setupRequest(Common.FastRand rng, ParkingLot.Builder request) {
+    public final Long setupRequest(Common.FastRand rng, ParkingLot.Builder request) {
         long result = 0;
         StructList.Builder<Car.Builder> cars = request.initCars(rng.nextLessThan(200));
         for (int i = 0; i < cars.size(); ++i) {
@@ -101,7 +102,7 @@ public class CarSales
     }
 
 
-    public void handleRequest(ParkingLot.Reader request, TotalValue.Builder response) {
+    public final void handleRequest(ParkingLot.Reader request, TotalValue.Builder response) {
         long result = 0;
         StructList.Reader<Car.Reader> cars = request.getCars();
         for (int i =0; i < cars.size(); ++i) {
@@ -110,7 +111,7 @@ public class CarSales
         response.setAmount(result);
     }
 
-    public boolean checkResponse(TotalValue.Reader response, Long expected) {
+    public final boolean checkResponse(TotalValue.Reader response, Long expected) {
         return response.getAmount() == expected;
     }
 
@@ -118,20 +119,11 @@ public class CarSales
     public static void main(String[] args) {
         Common.FastRand rng = new Common.FastRand();
 
-        TestCase<ParkingLot.Builder, ParkingLot.Reader,
-            TotalValue.Builder, TotalValue.Reader, Long> testCase = new CarSales();
+        TestCase<ParkingLot.Factory, ParkingLot.Builder, ParkingLot.Reader,
+            TotalValue.Factory, TotalValue.Builder, TotalValue.Reader, Long> testCase = new CarSales();
+
+        testCase.execute(ParkingLot.factory, TotalValue.factory);
 
-        for (int i = 0; i < 50000; ++i) {
-            MessageBuilder requestMessage = new MessageBuilder();
-            MessageBuilder responseMessage = new MessageBuilder();
-            ParkingLot.Builder request = requestMessage.initRoot(ParkingLot.factory);
-            long expected = testCase.setupRequest(rng, request);
-            TotalValue.Builder response = responseMessage.initRoot(TotalValue.factory);
-            testCase.handleRequest(request.asReader(), response);
-            if (!testCase.checkResponse(response.asReader(), expected)) {
-                System.out.println("mismatch!");
-            }
-        }
     }
 
 }
diff --git a/benchmark/src/main/java/org/capnproto/benchmark/Common.java b/benchmark/src/main/java/org/capnproto/benchmark/Common.java
index f9f6ce1..73ca64c 100644
--- a/benchmark/src/main/java/org/capnproto/benchmark/Common.java
+++ b/benchmark/src/main/java/org/capnproto/benchmark/Common.java
@@ -42,4 +42,6 @@ public class Common {
         return a % b;
     }
 
+
+
 }
diff --git a/benchmark/src/main/java/org/capnproto/benchmark/Eval.java b/benchmark/src/main/java/org/capnproto/benchmark/Eval.java
index 7112e31..65e5017 100644
--- a/benchmark/src/main/java/org/capnproto/benchmark/Eval.java
+++ b/benchmark/src/main/java/org/capnproto/benchmark/Eval.java
@@ -5,7 +5,10 @@ import org.capnproto.StructList;
 import org.capnproto.Text;
 import org.capnproto.benchmark.EvalSchema.*;
 
-public class Eval {
+public class Eval
+    extends TestCase<Expression.Factory, Expression.Builder, Expression.Reader,
+    EvaluationResult.Factory, EvaluationResult.Builder, EvaluationResult.Reader, Integer> {
+
     public static int makeExpression(Common.FastRand rng, Expression.Builder exp, int depth) {
         exp.setOp(Operation.values()[rng.nextLessThan(Operation.values().length)]);
 
@@ -67,4 +70,16 @@ public class Eval {
             throw new Error("impossible");
         }
     }
+
+    public final Integer setupRequest(Common.FastRand rng, Expression.Builder request) {
+        return makeExpression(rng, request, 0);
+    }
+
+    public final void handleRequest(Expression.Reader request, EvaluationResult.Builder response) {
+        response.setValue(evaluateExpression(request));
+    }
+
+    public final boolean checkResponse(EvaluationResult.Reader response, Integer expected) {
+        return response.getValue() == expected;
+    }
 }
diff --git a/benchmark/src/main/java/org/capnproto/benchmark/TestCase.java b/benchmark/src/main/java/org/capnproto/benchmark/TestCase.java
index f0e4082..29af2f5 100644
--- a/benchmark/src/main/java/org/capnproto/benchmark/TestCase.java
+++ b/benchmark/src/main/java/org/capnproto/benchmark/TestCase.java
@@ -2,9 +2,32 @@ package org.capnproto.benchmark;
 
 import org.capnproto.FromStructReader;
 import org.capnproto.FromStructBuilder;
+import org.capnproto.StructFactory;
+import org.capnproto.MessageBuilder;
 
-public interface TestCase<RequestBuilder, RequestReader, ResponseBuilder, ResponseReader, Expectation> {
-    public Expectation setupRequest(Common.FastRand rng, RequestBuilder request);
-    public void handleRequest(RequestReader request, ResponseBuilder response);
-    public boolean checkResponse(ResponseReader response, Expectation expected);
+public abstract class TestCase<RequestFactory extends StructFactory<RequestBuilder, RequestReader>,
+                          RequestBuilder, RequestReader,
+                          ResponseFactory extends StructFactory<ResponseBuilder, ResponseReader>,
+                          ResponseBuilder, ResponseReader, Expectation> {
+    public abstract Expectation setupRequest(Common.FastRand rng, RequestBuilder request);
+    public abstract void handleRequest(RequestReader request, ResponseBuilder response);
+    public abstract boolean checkResponse(ResponseReader response, Expectation expected);
+
+    public void execute(RequestFactory requestFactory, ResponseFactory responseFactory) {
+        Common.FastRand rng = new Common.FastRand();
+
+        for (int i = 0; i < 50000; ++i) {
+            MessageBuilder requestMessage = new MessageBuilder();
+            MessageBuilder responseMessage = new MessageBuilder();
+            RequestBuilder request = requestMessage.initRoot(requestFactory);
+            Expectation expected = this.setupRequest(rng, request);
+            ResponseBuilder response = responseMessage.initRoot(responseFactory);
+            this.handleRequest(requestFactory.asReader(request), response);
+            if (!this.checkResponse(responseFactory.asReader(response), expected)) {
+                System.out.println("mismatch!");
+            }
+        }
+
+
+    }
 }
diff --git a/compiler/src/main/cpp/capnpc-java.c++ b/compiler/src/main/cpp/capnpc-java.c++
index 49ee09c..698e000 100644
--- a/compiler/src/main/cpp/capnpc-java.c++
+++ b/compiler/src/main/cpp/capnpc-java.c++
@@ -1275,6 +1275,10 @@ private:
         spaces(indent), "    public final org.capnproto.StructSize structSize() {\n",
         spaces(indent), "      return ", fullName, ".STRUCT_SIZE;\n",
         spaces(indent), "    }\n",
+        spaces(indent), "    public final Reader asReader(Builder builder) {\n",
+        spaces(indent), "      return new Reader(builder._builder.asReader());\n",
+        spaces(indent), "    }\n",
+
         spaces(indent), "  }\n",
         spaces(indent), "  public static final Factory factory = new Factory();\n",
 
diff --git a/runtime/src/main/java/org/capnproto/StructFactory.java b/runtime/src/main/java/org/capnproto/StructFactory.java
index 9bd9c0a..9fa9742 100644
--- a/runtime/src/main/java/org/capnproto/StructFactory.java
+++ b/runtime/src/main/java/org/capnproto/StructFactory.java
@@ -1,4 +1,7 @@
 package org.capnproto;
 
 public interface StructFactory<Builder, Reader> extends FromStructBuilder<Builder>, FromStructReader<Reader>{
+
+    public Reader asReader(Builder builder);
+
 }