diff --git a/compiler/src/test/scala/org/capnproto/EncodingTest.scala b/compiler/src/test/scala/org/capnproto/EncodingTest.scala
index 48a3a4e..3bb8fc1 100644
--- a/compiler/src/test/scala/org/capnproto/EncodingTest.scala
+++ b/compiler/src/test/scala/org/capnproto/EncodingTest.scala
@@ -12,6 +12,7 @@ class EncodingSuite extends FunSuite {
     val allTypes = message.initRoot(TestAllTypes.Builder.factory);
     TestUtil.initTestMessage(allTypes);
     TestUtil.checkTestMessage(allTypes);
+    //TestUtil.checkTestMessage(allTypes.asReader());
   }
 
   test("AllTypesMultiSegment") {
diff --git a/compiler/src/test/scala/org/capnproto/TestUtil.scala b/compiler/src/test/scala/org/capnproto/TestUtil.scala
index 4813a55..eca6983 100644
--- a/compiler/src/test/scala/org/capnproto/TestUtil.scala
+++ b/compiler/src/test/scala/org/capnproto/TestUtil.scala
@@ -89,4 +89,44 @@ object TestUtil {
     assert(builder.getVoidList().size() == 6);
   }
 
+  def checkTestMessage(reader : TestAllTypes.Reader) {
+    reader.getVoidField();
+    assert(reader.getBoolField() == true);
+    assert(reader.getInt8Field() == -123);
+    assert(reader.getInt16Field() == -12345);
+    assert(reader.getInt32Field() == -12345678);
+    assert(reader.getInt64Field() == -123456789012345L);
+    assert(reader.getUInt8Field() == 0xef.toByte);
+    assert(reader.getUInt16Field() == 0x4567);
+    assert(reader.getUInt32Field() == 0x34567890);
+    assert(reader.getUInt64Field() == 0x1234567890123456L);
+    assert(reader.getFloat32Field() == 1234.5f);
+    assert(reader.getFloat64Field() == -123e45);
+    assert(reader.getTextField().toString() == "foo");
+
+    {
+      val subReader = reader.getStructField();
+      subReader.getVoidField();
+      assert(subReader.getBoolField() == true);
+      assert(subReader.getInt8Field() == -12);
+      assert(subReader.getInt16Field() == 3456);
+      assert(subReader.getInt32Field() == -78901234);
+      assert(subReader.getInt64Field() == 56789012345678L);
+      assert(subReader.getUInt8Field() == 90);
+      assert(subReader.getUInt16Field() == 1234);
+      assert(subReader.getUInt32Field() == 56789012);
+      assert(subReader.getUInt64Field() == 345678901234567890L);
+      assert(subReader.getFloat32Field() == -1.25e-10f);
+      assert(subReader.getFloat64Field() == 345);
+
+      {
+        val subSubReader = subReader.getStructField();
+        assert(subSubReader.getTextField().toString() == "nested")
+      }
+    }
+
+    assert(reader.getVoidList().size() == 6);
+  }
+
+
 }
diff --git a/runtime/src/main/java/org/capnproto/BuilderArena.java b/runtime/src/main/java/org/capnproto/BuilderArena.java
index 6e7e61f..ff17f79 100644
--- a/runtime/src/main/java/org/capnproto/BuilderArena.java
+++ b/runtime/src/main/java/org/capnproto/BuilderArena.java
@@ -33,7 +33,7 @@ public final class BuilderArena implements Arena {
     }
 
     public SegmentReader tryGetSegment(int id) {
-        throw new Error("unimplemented");
+        return this.segments.get(id);
     }
     public SegmentBuilder getSegment(int id) {
         return this.segments.get(id);
diff --git a/runtime/src/main/java/org/capnproto/InputStreamMessageReader.java b/runtime/src/main/java/org/capnproto/InputStreamMessageReader.java
index 489b865..5435d0b 100644
--- a/runtime/src/main/java/org/capnproto/InputStreamMessageReader.java
+++ b/runtime/src/main/java/org/capnproto/InputStreamMessageReader.java
@@ -4,7 +4,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
-import java.util.Vector;
+import java.util.ArrayList;
 
 public final class InputStreamMessageReader {
 
@@ -47,7 +47,7 @@ public final class InputStreamMessageReader {
         }
 
         // in words
-        Vector<Integer> moreSizes = new Vector<Integer>();
+        ArrayList<Integer> moreSizes = new ArrayList<Integer>();
 
         if (segmentCount > 1) {
             ByteBuffer moreSizesRaw = makeByteBuffer(readExact(is, 4 * (segmentCount & ~1)));
diff --git a/runtime/src/main/java/org/capnproto/MessageReader.java b/runtime/src/main/java/org/capnproto/MessageReader.java
index 3aed7ce..fa2e564 100644
--- a/runtime/src/main/java/org/capnproto/MessageReader.java
+++ b/runtime/src/main/java/org/capnproto/MessageReader.java
@@ -3,14 +3,14 @@ package org.capnproto;
 import java.nio.ByteBuffer;
 
 public final class MessageReader {
-    final ByteBuffer[] segmentSlices;
+    final ReaderArena arena;
 
     public MessageReader(ByteBuffer[] segmentSlices) {
-        this.segmentSlices = segmentSlices;
+        this.arena = new ReaderArena(segmentSlices);
     }
 
     public <T> T getRoot(FromStructReader<T> factory) {
-        SegmentReader segment = new SegmentReader(this.segmentSlices[0], new ReaderArena());
+        SegmentReader segment = this.arena.tryGetSegment(0);
         PointerReader pointerReader = PointerReader.getRoot(segment, 0,
                                                             0x7fffffff /* XXX */);
         AnyPointer.Reader any = new AnyPointer.Reader(pointerReader);
diff --git a/runtime/src/main/java/org/capnproto/ReaderArena.java b/runtime/src/main/java/org/capnproto/ReaderArena.java
index a90d740..c40fc1b 100644
--- a/runtime/src/main/java/org/capnproto/ReaderArena.java
+++ b/runtime/src/main/java/org/capnproto/ReaderArena.java
@@ -1,7 +1,20 @@
 package org.capnproto;
 
+import java.util.ArrayList;
+import java.nio.ByteBuffer;
+
 public final class ReaderArena implements Arena {
+
+    public final ArrayList<SegmentReader> segments;
+
+    public ReaderArena(ByteBuffer[] segmentSlices) {
+        this.segments = new ArrayList<SegmentReader>();
+        for(int ii = 0; ii < segmentSlices.length; ++ii) {
+            this.segments.add(new SegmentReader(segmentSlices[ii], this));
+        }
+    }
+
     public SegmentReader tryGetSegment(int id) {
-        throw new Error("unimplemented");
+        return segments.get(id);
     }
 }
diff --git a/runtime/src/test/scala/org/capnproto/LayoutTest.scala b/runtime/src/test/scala/org/capnproto/LayoutTest.scala
index fa1b639..c7ac0c2 100644
--- a/runtime/src/test/scala/org/capnproto/LayoutTest.scala
+++ b/runtime/src/test/scala/org/capnproto/LayoutTest.scala
@@ -13,7 +13,8 @@ class LayoutSuite extends FunSuite {
     val buffer = java.nio.ByteBuffer.wrap(data);
     buffer.order(java.nio.ByteOrder.LITTLE_ENDIAN);
 
-    val pointerReader = new PointerReader(new SegmentReader(buffer, new ReaderArena()), 0, 0x7fffffff);
+    val arena = new ReaderArena(Array(buffer));
+    val pointerReader = new PointerReader(arena.tryGetSegment(0), 0, 0x7fffffff);
     val reader = pointerReader.getStruct();
 
     assert(reader.getLongField(0) === 0xefcdab8967452301L);