diff --git a/src/test/scala/tlschannel/InteroperabilityTest.scala b/src/test/scala/tlschannel/InteroperabilityTest.scala
index 95f6ebb7..eb84c12a 100644
--- a/src/test/scala/tlschannel/InteroperabilityTest.scala
+++ b/src/test/scala/tlschannel/InteroperabilityTest.scala
@@ -1,35 +1,30 @@
 package tlschannel
 
 import scala.util.Random
-import java.net.Socket
-import java.nio.channels.ByteChannel
-import javax.net.ssl.SSLSocket
-import java.nio.ByteBuffer
 import org.junit.jupiter.api.Assertions.{assertArrayEquals, assertEquals, assertNotEquals, assertTrue}
 import org.junit.jupiter.api.{Test, TestInstance}
 import org.junit.jupiter.api.TestInstance.Lifecycle
 import tlschannel.helpers.TestUtil
 import tlschannel.helpers.SslContextFactory
 import tlschannel.helpers.SocketPairFactory
+import tlschannel.util.InteroperabilityUtils._
 
 @TestInstance(Lifecycle.PER_CLASS)
 class InteroperabilityTest {
 
-  import InteroperabilityTest._
-
   val sslContextFactory = new SslContextFactory
   val factory = new SocketPairFactory(sslContextFactory.defaultContext, SslContextFactory.certificateCommonName)
 
   def oldNio() = {
     val (client, server) = factory.oldNio(None)
     val clientPair = (new SSLSocketWriter(client), new SocketReader(client))
-    val serverPair = (new TlsSocketChannelWriter(server.tls), new ByteChannelReader(server.tls))
+    val serverPair = (new TlsChannelWriter(server.tls), new ByteChannelReader(server.tls))
     (clientPair, serverPair)
   }
 
   def nioOld() = {
     val (client, server) = factory.nioOld()
-    val clientPair = (new TlsSocketChannelWriter(client.tls), new ByteChannelReader(client.tls))
+    val clientPair = (new TlsChannelWriter(client.tls), new ByteChannelReader(client.tls))
     val serverPair = (new SSLSocketWriter(server), new SocketReader(server))
     (clientPair, serverPair)
   }
@@ -165,50 +160,3 @@ class InteroperabilityTest {
   }
 
 }
-
-object InteroperabilityTest {
-
-  trait Reader {
-    def read(array: Array[Byte], offset: Int, length: Int): Int
-    def close(): Unit
-  }
-
-  class SocketReader(socket: Socket) extends Reader {
-    private val is = socket.getInputStream
-    def read(array: Array[Byte], offset: Int, length: Int) = is.read(array, offset, length)
-    def close() = socket.close()
-  }
-
-  class ByteChannelReader(socket: ByteChannel) extends Reader {
-    def read(array: Array[Byte], offset: Int, length: Int) = socket.read(ByteBuffer.wrap(array, offset, length))
-    def close() = socket.close()
-  }
-
-  trait Writer {
-    def renegotiate(): Unit
-    def write(array: Array[Byte], offset: Int, length: Int): Unit
-    def close(): Unit
-  }
-
-  class SSLSocketWriter(socket: SSLSocket) extends Writer {
-    private val os = socket.getOutputStream
-    def write(array: Array[Byte], offset: Int, length: Int) = os.write(array, offset, length)
-    def renegotiate() = socket.startHandshake()
-    def close() = socket.close()
-  }
-
-  class TlsSocketChannelWriter(val socket: TlsChannel) extends Writer {
-
-    def write(array: Array[Byte], offset: Int, length: Int) = {
-      val buffer = ByteBuffer.wrap(array, offset, length)
-      while (buffer.remaining() > 0) {
-        val c = socket.write(buffer)
-        assertNotEquals(0, c, "blocking write cannot return 0")
-      }
-    }
-
-    def renegotiate(): Unit = socket.renegotiate()
-    def close() = socket.close()
-  }
-
-}
diff --git a/src/test/scala/tlschannel/util/InteroperabilityUtils.java b/src/test/scala/tlschannel/util/InteroperabilityUtils.java
new file mode 100644
index 00000000..af0d8733
--- /dev/null
+++ b/src/test/scala/tlschannel/util/InteroperabilityUtils.java
@@ -0,0 +1,122 @@
+package tlschannel.util;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.Socket;
+import java.nio.ByteBuffer;
+import java.nio.channels.ByteChannel;
+import javax.net.ssl.SSLSocket;
+import org.junit.jupiter.api.Assertions;
+import tlschannel.TlsChannel;
+
+public class InteroperabilityUtils {
+
+    public interface Reader {
+        int read(byte[] array, int offset, int length) throws IOException;
+
+        void close() throws IOException;
+    }
+
+    public interface Writer {
+        void renegotiate() throws IOException;
+
+        void write(byte[] array, int offset, int length) throws IOException;
+
+        void close() throws IOException;
+    }
+
+    public static class SocketReader implements Reader {
+
+        private final Socket socket;
+        private final InputStream is;
+
+        public SocketReader(Socket socket) throws IOException {
+            this.socket = socket;
+            this.is = socket.getInputStream();
+        }
+
+        @Override
+        public int read(byte[] array, int offset, int length) throws IOException {
+            return is.read(array, offset, length);
+        }
+
+        @Override
+        public void close() throws IOException {
+            socket.close();
+        }
+    }
+
+    public static class ByteChannelReader implements Reader {
+
+        private final ByteChannel socket;
+
+        public ByteChannelReader(ByteChannel socket) {
+            this.socket = socket;
+        }
+
+        @Override
+        public int read(byte[] array, int offset, int length) throws IOException {
+            return socket.read(ByteBuffer.wrap(array, offset, length));
+        }
+
+        @Override
+        public void close() throws IOException {
+            socket.close();
+        }
+    }
+
+    public static class SSLSocketWriter implements Writer {
+
+        private final SSLSocket socket;
+        private final OutputStream os;
+
+        public SSLSocketWriter(SSLSocket socket) throws IOException {
+            this.socket = socket;
+            this.os = socket.getOutputStream();
+        }
+
+        @Override
+        public void write(byte[] array, int offset, int length) throws IOException {
+            os.write(array, offset, length);
+        }
+
+        @Override
+        public void renegotiate() throws IOException {
+            socket.startHandshake();
+        }
+
+        @Override
+        public void close() throws IOException {
+            socket.close();
+        }
+    }
+
+    public static class TlsChannelWriter implements Writer {
+
+        private final TlsChannel socket;
+
+        public TlsChannelWriter(TlsChannel socket) {
+            this.socket = socket;
+        }
+
+        @Override
+        public void write(byte[] array, int offset, int length) throws IOException {
+            ByteBuffer buffer = ByteBuffer.wrap(array, offset, length);
+            while (buffer.remaining() > 0) {
+                int c = socket.write(buffer);
+                Assertions.assertNotEquals(0, c, "blocking write cannot return 0");
+            }
+        }
+
+        @Override
+        public void renegotiate() throws IOException {
+            socket.renegotiate();
+        }
+
+        @Override
+        public void close() throws IOException {
+            socket.close();
+        }
+    }
+}