diff --git a/java-classfile.cabal b/java-classfile.cabal
index 1b1f151..abee9b8 100644
--- a/java-classfile.cabal
+++ b/java-classfile.cabal
@@ -38,6 +38,7 @@ library
       Language.Java.Classfile.Flag
       Language.Java.Classfile.Flags
       Language.Java.Classfile.FromBigEndian
+      Language.Java.Classfile.Interfaces
       Language.Java.Classfile.Magic
       Language.Java.Classfile.Version
   other-modules:
diff --git a/src/Language/Java/Classfile.hs b/src/Language/Java/Classfile.hs
index f115291..00507bb 100644
--- a/src/Language/Java/Classfile.hs
+++ b/src/Language/Java/Classfile.hs
@@ -9,6 +9,7 @@ import Language.Java.Classfile.ConstantPool (ConstantPool)
 import Language.Java.Classfile.Flags (Flags)
 import Language.Java.Classfile.ClassFlag (ClassFlag)
 import Language.Java.Classfile.ConstantPool.References (ClassReference)
+import Language.Java.Classfile.Interfaces (Interfaces)
 
 data Classfile = Classfile
   { magic        :: Magic
@@ -17,6 +18,7 @@ data Classfile = Classfile
   , accessFlags  :: Flags ClassFlag
   , this         :: ClassReference
   , super        :: ClassReference
+  , interfaces   :: Interfaces
   }
   deriving stock (Show, Generic)
   deriving Extractable via Generically Classfile
diff --git a/src/Language/Java/Classfile/ConstantPool.hs b/src/Language/Java/Classfile/ConstantPool.hs
index 006d492..946706a 100644
--- a/src/Language/Java/Classfile/ConstantPool.hs
+++ b/src/Language/Java/Classfile/ConstantPool.hs
@@ -1,11 +1,20 @@
 {-# LANGUAGE DerivingStrategies #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE InstanceSigs #-}
+{-# LANGUAGE TypeApplications #-}
 module Language.Java.Classfile.ConstantPool (ConstantPool(..)) where
 import Data.Word (Word16)
-import Data.Array.IArray (Array)
+import Data.Array.IArray (Array, listArray)
 import Language.Java.Classfile.ConstantPool.Entry (Entry)
-import Language.Java.Classfile.Extractable (Extractable)
+import Language.Java.Classfile.Extractable (Extractable (extract))
+import Language.Java.Classfile.Extract (Extract, traceIndex)
+import Control.Monad (forM)
 
 newtype ConstantPool = ConstantPool (Array Word16 Entry)
   deriving stock (Show)
-  deriving newtype Extractable
+
+instance Extractable ConstantPool where
+  extract :: Extract ConstantPool
+  extract = do
+    count <- extract @Word16
+    elements <- forM [1..fromIntegral count - 1] $ \ i -> traceIndex i extract
+    pure . ConstantPool $ listArray (1, count - 1) elements
diff --git a/src/Language/Java/Classfile/Extractable.hs b/src/Language/Java/Classfile/Extractable.hs
index e46f8ad..109e7d4 100644
--- a/src/Language/Java/Classfile/Extractable.hs
+++ b/src/Language/Java/Classfile/Extractable.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE InstanceSigs #-}
+{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE UndecidableInstances #-}
@@ -24,7 +25,7 @@ import GHC.Float (castWord32ToFloat, castWord64ToDouble)
 import qualified Data.Text as Text
 import GHC.TypeLits (symbolVal, KnownSymbol)
 import Data.Proxy (Proxy(Proxy))
-import Data.Typeable (Typeable)
+import Data.Typeable (Typeable, typeRep)
 
 class Extractable a where
   extract :: Extract a
@@ -61,12 +62,24 @@ instance Extractable Int64 where
 
     pure $ (fromIntegral high `shiftL` 32) .|. fromIntegral low
 
-instance (Extractable index, Extractable element, Ix index, Integral index) => Extractable (Array index element) where
+instance (Extractable index, Extractable element, Ix index, Integral index, Show index, Typeable element) => Extractable (Array index element) where
   extract :: Extract (Array index element)
   extract = do
     count <- extract
-    elements <- forM [1..fromIntegral count - 1] $ \ i -> traceIndex i extract
-    pure $ listArray (1, count - 1) elements
+
+    let typeName = Text.concat
+          [ "Array (0, "
+          , Text.pack . show $ count
+          , ") "
+          , (Text.pack . show) (typeRep (Proxy :: Proxy element))
+          ]
+
+    if count == 0
+      then pure $ listArray (1, 0) []
+      else traceType typeName $ do
+
+        elements <- forM [0..fromIntegral count] $ \ i -> traceIndex i extract
+        pure $ listArray (1, count) elements
 
 deriving via Generically () instance Extractable ()
 deriving via Generically (a, b) instance (Extractable a, Extractable b) => Extractable (a, b)
diff --git a/src/Language/Java/Classfile/Interfaces.hs b/src/Language/Java/Classfile/Interfaces.hs
new file mode 100644
index 0000000..6c4f485
--- /dev/null
+++ b/src/Language/Java/Classfile/Interfaces.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DerivingVia #-}
+module Language.Java.Classfile.Interfaces (Interfaces(..)) where
+import Data.Array.IArray (Array)
+import Data.Word (Word16)
+import Language.Java.Classfile.ConstantPool.References (ClassReference)
+import Language.Java.Classfile.Extractable (Extractable)
+import GHC.Generics ( Generic, Generically, Generically(..) )
+
+newtype Interfaces = Interfaces (Array Word16 ClassReference)
+  deriving stock (Show, Generic)
+  deriving Extractable via Generically Interfaces