diff --git a/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/CursorOperation.java b/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/CursorOperation.java
index cc95c65..0c25858 100644
--- a/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/CursorOperation.java
+++ b/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/CursorOperation.java
@@ -15,7 +15,7 @@ import java.io.IOException;
 /**
  * @author aNNiMON
  */
-public class CursorOperation implements Operation {
+public class CursorOperation extends Operation {
 
     private static final int
             NONE = -1,
@@ -26,9 +26,6 @@ public class CursorOperation implements Operation {
             TYPE_KEY_RELEASED = 5,
             STOP = 10;
 
-    private DataInputStream dis;
-    private DataOutputStream dos;
-
     private boolean running;
 
     public CursorOperation(DataInputStream dis) {
diff --git a/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/FileOperation.java b/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/FileOperation.java
index 96300c5..6f16e4e 100644
--- a/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/FileOperation.java
+++ b/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/FileOperation.java
@@ -16,13 +16,10 @@ import java.io.IOException;
  *
  * @author aNNiMON
  */
-public class FileOperation implements Operation {
+public class FileOperation extends Operation {
 
     private static final int BUFFER_SIZE = 1024;
 
-    private DataInputStream dis;
-    private DataOutputStream dos;
-
     public FileOperation(DataInputStream dis) {
         this.dis = dis;
     }
diff --git a/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/MessageOperation.java b/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/MessageOperation.java
index da550a3..1bc9483 100644
--- a/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/MessageOperation.java
+++ b/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/MessageOperation.java
@@ -12,10 +12,7 @@ import java.io.IOException;
  *
  * @author aNNiMON
  */
-public class MessageOperation implements Operation {
-
-    private DataInputStream dis;
-    private DataOutputStream dos;
+public class MessageOperation extends Operation {
 
     public MessageOperation(DataInputStream dis) {
         this.dis = dis;
diff --git a/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/Operation.java b/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/Operation.java
index 2360e8d..ec6d2e9 100644
--- a/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/Operation.java
+++ b/SocketFileTransfer/src/main/java/com/annimon/socketfiletransfer/operations/Operation.java
@@ -1,13 +1,19 @@
 package com.annimon.socketfiletransfer.operations;
 
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+
 /**
  *
  * @author aNNiMON
  */
-public interface Operation {
+public abstract class Operation {
 
-    void startServerSide() throws Exception;
+    protected DataInputStream dis;
+    protected DataOutputStream dos;
 
-    void startClientSide(Object... params) throws Exception;
+    public abstract void startServerSide() throws Exception;
+
+    public abstract void startClientSide(Object... params) throws Exception;
 
 }
\ No newline at end of file