Added garbage collection for disconnected players

- Heartbeat messages are sent out from their own thread to each player
- If a heartbeat message can't be sent to a player, they are removed from the list of players
- Added equals method for players
Tags: #story[1047]

src/main/java/seng302/gameServer/HeartbeatThread.java

@@ -0,0 +1,81 @@
+package seng302.gameServer;
+
+import seng302.models.Player;
+import seng302.server.messages.Heartbeat;
+import seng302.server.messages.Message;
+
+import java.io.IOException;
+import java.util.*;
+
+/**
+ * Send Heartbeat messages to connected player at a specified interval
+ * Will call .clientDisconnected on the delegate when a heartbeat message
+ * cannot be sent to a player
+ */
+public class HeartbeatThread extends Thread{
+    private final int HEARTBEAT_PERIOD = 5000;
+    private ClientConnectionDelegate delegate;
+    private Integer seqNum;
+    private Stack<Player> disconnectedPlayers;
+
+    HeartbeatThread(ClientConnectionDelegate delegate){
+        this.delegate =  delegate;
+        seqNum = 0;
+        disconnectedPlayers = new Stack<>();
+    }
+
+    /**
+     * A player has lost connection to the server
+     * The player is added to a stack so that the delegate
+     * can be notified
+     *
+     * @param player The player that has disconnected
+     */
+    private void playerLostConnection(Player player){
+        disconnectedPlayers.push(player);
+    }
+
+    /**
+     * Sends a heartbeat message to each connected player
+     * The delegate is notified if a player has disconnected
+     */
+    private void sendHeartbeatToAllPlayers(){
+        Message heartbeat = new Heartbeat(seqNum);
+
+        for (Player player : GameState.getPlayers()){
+            if (!player.getSocketChannel().isConnected()){
+                playerLostConnection(player);
+            }
+
+            try {
+                heartbeat.send(player.getSocketChannel());
+            } catch (IOException e) {
+                playerLostConnection(player);
+            }
+        }
+
+        updateDelegate();
+        seqNum++;
+    }
+
+    /**
+     * Notifies the delegate about
+     * each disconnected player
+     */
+    private void updateDelegate() {
+        while (!disconnectedPlayers.empty()){
+            delegate.clientDisconnected(disconnectedPlayers.pop());
+        }
+    }
+
+    public void run(){
+        Timer t = new Timer();
+
+        t.schedule(new TimerTask() {
+            @Override
+            public void run() {
+                sendHeartbeatToAllPlayers();
+            }
+        }, 0, HEARTBEAT_PERIOD);
+    }
+}