diff --git a/src/kademlia/core/KadServer.java b/src/kademlia/core/KadServer.java
index 5c07fac..df54107 100644
--- a/src/kademlia/core/KadServer.java
+++ b/src/kademlia/core/KadServer.java
@@ -14,6 +14,7 @@ import java.net.DatagramPacket;
 import java.net.DatagramSocket;
 import java.net.SocketException;
 import java.util.HashMap;
+import java.util.Map;
 import java.util.Random;
 import java.util.Timer;
 import java.util.TimerTask;
@@ -32,9 +33,9 @@ public class KadServer
     private final int udpPort;
     private final DatagramSocket socket;
     private boolean isRunning;
-    private final HashMap<Integer, Receiver> receivers;
+    private final Map<Integer, Receiver> receivers;
     private final Timer timer;      // Schedule future tasks
-    private final HashMap<Integer, TimerTask> tasks;    // Keep track of scheduled tasks
+    private final Map<Integer, TimerTask> tasks;    // Keep track of scheduled tasks
 
     private final Node localNode;
 
diff --git a/src/kademlia/dht/StorageEntryManager.java b/src/kademlia/dht/StorageEntryManager.java
index e54d79c..674f74b 100644
--- a/src/kademlia/dht/StorageEntryManager.java
+++ b/src/kademlia/dht/StorageEntryManager.java
@@ -2,6 +2,8 @@ package kademlia.dht;
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 import kademlia.node.NodeId;
 
 /**
@@ -15,7 +17,7 @@ import kademlia.node.NodeId;
 public class StorageEntryManager
 {
 
-    private final HashMap<NodeId, ArrayList<StorageEntry>> entries;
+    private final Map<NodeId, List<StorageEntry>> entries;
 
     
     {
@@ -60,7 +62,7 @@ public class StorageEntryManager
      *
      * @return List of content for the specific search parameters
      */
-    public ArrayList<StorageEntry> get(NodeId key)
+    public List<StorageEntry> get(NodeId key)
     {
         return this.entries.get(key);
     }
diff --git a/src/kademlia/message/NodeLookupReceiver.java b/src/kademlia/message/NodeLookupReceiver.java
index 5119ec8..f3a4901 100644
--- a/src/kademlia/message/NodeLookupReceiver.java
+++ b/src/kademlia/message/NodeLookupReceiver.java
@@ -6,7 +6,7 @@
 package kademlia.message;
 
 import java.io.IOException;
-import java.util.ArrayList;
+import java.util.List;
 import kademlia.core.Configuration;
 import kademlia.core.KadServer;
 import kademlia.node.Node;
@@ -45,7 +45,7 @@ public class NodeLookupReceiver implements Receiver
         this.localNode.getRoutingTable().insert(origin);
 
         /* Find nodes closest to the LookupId */
-        ArrayList<Node> nodes = this.localNode.getRoutingTable().findClosest(msg.getLookupId(), Configuration.K);
+        List<Node> nodes = this.localNode.getRoutingTable().findClosest(msg.getLookupId(), Configuration.K);
 
         System.out.println("\nClosest Nodes: ");
         for (Node n : nodes)
diff --git a/src/kademlia/message/NodeReplyMessage.java b/src/kademlia/message/NodeReplyMessage.java
index 746867e..3312c85 100644
--- a/src/kademlia/message/NodeReplyMessage.java
+++ b/src/kademlia/message/NodeReplyMessage.java
@@ -5,12 +5,11 @@
  */
 package kademlia.message;
 
-import java.io.DataInput;
 import java.io.DataInputStream;
-import java.io.DataOutput;
 import java.io.DataOutputStream;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.List;
 import kademlia.node.Node;
 
 public class NodeReplyMessage implements Message
@@ -18,9 +17,9 @@ public class NodeReplyMessage implements Message
 
     private Node origin;
     public static final byte CODE = 0x04;
-    private ArrayList<Node> nodes;
+    private List<Node> nodes;
 
-    public NodeReplyMessage(Node origin, ArrayList<Node> nodes)
+    public NodeReplyMessage(Node origin, List<Node> nodes)
     {
         this.origin = origin;
         this.nodes = nodes;
@@ -80,7 +79,7 @@ public class NodeReplyMessage implements Message
         return CODE;
     }
 
-    public ArrayList<Node> getNodes()
+    public List<Node> getNodes()
     {
         return this.nodes;
     }
diff --git a/src/kademlia/operation/NodeLookupOperation.java b/src/kademlia/operation/NodeLookupOperation.java
index d7c29a6..26bd59c 100644
--- a/src/kademlia/operation/NodeLookupOperation.java
+++ b/src/kademlia/operation/NodeLookupOperation.java
@@ -45,7 +45,7 @@ public class NodeLookupOperation implements Operation, Receiver
     private final SortedMap<Node, Byte> nodes;
 
     /* Tracks messages in transit and awaiting reply */
-    private final HashMap<Integer, Node> messagesTransiting;
+    private final Map<Integer, Node> messagesTransiting;
 
     /* Used to sort nodes */
     private final Comparator comparator;
@@ -83,7 +83,7 @@ public class NodeLookupOperation implements Operation, Receiver
      * @throws kademlia.exceptions.RoutingException
      */
     @Override
-    public synchronized ArrayList<Node> execute() throws IOException, RoutingException
+    public synchronized List<Node> execute() throws IOException, RoutingException
     {
         try
         {
@@ -159,7 +159,7 @@ public class NodeLookupOperation implements Operation, Receiver
         }
 
         /* Get unqueried nodes among the K closest seen that have not FAILED */
-        ArrayList<Node> unasked = this.closestNodesNotFailed(UNASKED);
+        List<Node> unasked = this.closestNodesNotFailed(UNASKED);
         for (Node nn : unasked)
         {
             System.out.println(nn.getNodeId());
@@ -198,9 +198,9 @@ public class NodeLookupOperation implements Operation, Receiver
      *
      * @return The K closest nodes to the target lookupId given that have the specified status
      */
-    private ArrayList<Node> closestNodes(Byte status)
+    private List<Node> closestNodes(Byte status)
     {
-        ArrayList<Node> closestNodes = new ArrayList<>(Configuration.K);
+        List<Node> closestNodes = new ArrayList<>(Configuration.K);
         int remainingSpaces = Configuration.K;
 
         for (Map.Entry e : this.nodes.entrySet())
@@ -227,9 +227,9 @@ public class NodeLookupOperation implements Operation, Receiver
      *
      * @return A List of the closest nodes
      */
-    private ArrayList<Node> closestNodesNotFailed(Byte status)
+    private List<Node> closestNodesNotFailed(Byte status)
     {
-        ArrayList<Node> closestNodes = new ArrayList<>(Configuration.K);
+        List<Node> closestNodes = new ArrayList<>(Configuration.K);
         int remainingSpaces = Configuration.K;
 
         for (Map.Entry e : this.nodes.entrySet())
diff --git a/src/kademlia/operation/StoreOperation.java b/src/kademlia/operation/StoreOperation.java
index 1d8a963..07ce27c 100644
--- a/src/kademlia/operation/StoreOperation.java
+++ b/src/kademlia/operation/StoreOperation.java
@@ -1,7 +1,7 @@
 package kademlia.operation;
 
 import java.io.IOException;
-import java.util.ArrayList;
+import java.util.List;
 import kademlia.core.KadServer;
 import kademlia.dht.KadContent;
 import kademlia.message.Message;
@@ -37,7 +37,7 @@ public class StoreOperation implements Operation
     public synchronized Object execute() throws IOException
     {
         /* Get the nodes on which we need to store the content */
-        ArrayList<Node> nodes = new NodeLookupOperation(this.server, this.localNode, this.content.getKey()).execute();
+        List<Node> nodes = new NodeLookupOperation(this.server, this.localNode, this.content.getKey()).execute();
         System.out.println("Nodes to put content on: " + nodes);
 
         /* Create the message */
diff --git a/src/kademlia/routing/KadBucket.java b/src/kademlia/routing/KadBucket.java
index d846f46..925668a 100644
--- a/src/kademlia/routing/KadBucket.java
+++ b/src/kademlia/routing/KadBucket.java
@@ -7,6 +7,8 @@ package kademlia.routing;
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 import kademlia.node.Node;
 import kademlia.node.NodeId;
 
@@ -14,7 +16,7 @@ public class KadBucket implements Bucket
 {
 
     private final int depth;
-    private final HashMap<NodeId, Node> nodes;
+    private final Map<NodeId, Node> nodes;
 
     
     {
@@ -85,7 +87,7 @@ public class KadBucket implements Bucket
         this.nodes.remove(n.getNodeId());
     }
 
-    public ArrayList<Node> getNodes()
+    public List<Node> getNodes()
     {
         return new ArrayList<>(this.nodes.values());
     }
diff --git a/src/kademlia/routing/RoutingTable.java b/src/kademlia/routing/RoutingTable.java
index 3feb30c..fe5ad63 100644
--- a/src/kademlia/routing/RoutingTable.java
+++ b/src/kademlia/routing/RoutingTable.java
@@ -6,6 +6,7 @@
 package kademlia.routing;
 
 import java.util.ArrayList;
+import java.util.List;
 import kademlia.node.Node;
 import kademlia.node.NodeId;
 
@@ -72,11 +73,11 @@ public class RoutingTable
      * @param target The NodeId to find contacts close to
      * @param num    The number of contacts to find
      *
-     * @return ArrayList<Contact> An ArrayList of num contacts closest to target
+     * @return List<Contact> A List of num contacts closest to target
      */
-    public ArrayList<Node> findClosest(NodeId target, int num)
+    public List<Node> findClosest(NodeId target, int num)
     {
-        ArrayList<Node> closest = new ArrayList<>(num);
+        List<Node> closest = new ArrayList<>(num);
 
         /* Get the bucket number to search for closest from */
         int bucketNumber = this.localNode.getNodeId().xor(target).getFirstSetBitIndex() - 1;
@@ -144,9 +145,9 @@ public class RoutingTable
         return closest;
     }
 
-    public ArrayList<Node> getAllNodes()
+    public List<Node> getAllNodes()
     {
-        ArrayList<Node> nodes = new ArrayList<>();
+        List<Node> nodes = new ArrayList<>();
 
         for (KadBucket b : this.buckets)
         {