Lift better abstractions

lift/src/lift/Door.java

@@ -1,25 +1,46 @@
 package lift;
 
 class Door {
-  private boolean open;
+    private boolean open;
+    private int passengersEntering;
+    private int passengersExiting;
 
-  /** Create a new closed door */
-  public Door() {
-    open = false;
-  }
+    /** Create a new closed door */
+    public Door() {
+        open = false;
+        passengersEntering = 0;
+        passengersExiting = 0;
+    }
 
-  /** Returns true if door is open */
-  public boolean isOpen() {
-    return open;
-  }
+    /** Returns true if door is open */
+    public boolean isOpen() {
+        return open;
+    }
 
-  /** Open the door */
-  public void open() {
-    open = true;
-  }
+    /** Open the door */
+    public void open() {
+        open = true;
+    }
+
+    /** Close the door */
+    public void close() {
+        open = false;
+    }
+
+    public int getEntering() {
+        return passengersEntering;
+    }
+
+    public void setEntering(int passengers) {
+        this.passengersEntering = passengers;
+    }
+
+    public int getExiting() {
+        return passengersExiting;
+    }
+
+    public void setExiting(int passengers) {
+        this.passengersExiting = passengers;
+    }
 
-  /** Close the door */
-  public void close() {
-    open = false;
-  }
 }

lift/src/lift/LiftMonitor.java

@@ -18,9 +18,9 @@ public class LiftMonitor {
   /** Current direction of the lift */
   private Direction direction;
   /** number of passengers waiting to enter the lift at the various floors */
-  private int[] waitEntry;
+  // private int[] waitEntry;
   /** number of passengers (in lift) waiting to leave at the various floors */
-  private int[] waitExit;
+  // private int[] waitExit;
   /** number of passengers currently in the lift */
   private int load;
   /** view object passed from main */
@@ -32,6 +32,9 @@ public class LiftMonitor {
   /** Counter of number of passengers currently exiting the elevator */
   private int passengersExiting;
 
+  private PassengerQueue waitEntry;
+  private PassengerQueue waitExit;
+
   /** Create new LiftMonitor */
   public LiftMonitor(LiftView v, int floors) {
     floor = 0;
@@ -39,8 +42,8 @@ public class LiftMonitor {
     moving = true;
     direction = Direction.UP;
     door = new Door();
-    waitEntry = new int[nfloors];
-    waitExit = new int[nfloors];
+    waitEntry = new PassengerQueue(nfloors);
+    waitExit = new PassengerQueue(nfloors);
     load = 0;
     view = v;
     passengersEntering = 0;
@@ -49,7 +52,7 @@ public class LiftMonitor {
 
   /** Increases the number of waiting passengers on given floor */
   public synchronized void increaseWaitEntry(int passengerFloor) {
-    waitEntry[passengerFloor]++;
+    waitEntry.inc(passengerFloor);
     notifyAll();
   }
 
@@ -64,8 +67,9 @@ public class LiftMonitor {
         throw new Error("Monitor.enterLift interrupted " + e);
       }
     }
-    waitEntry[floor]--;
-    waitExit[passengerDestination]++;
+
+    waitEntry.dec(floor);
+    waitExit.inc(passengerDestination);
     load++;
     passengersEntering++;
     notifyAll();
@@ -86,7 +90,7 @@ public class LiftMonitor {
         throw new Error("Monitor.exitLift interrupted " + e);
       }
     }
-    waitExit[passengerDestination]--;
+    waitExit.dec(passengerDestination);
     load--;
     passengersExiting++;
     notifyAll();
@@ -104,9 +108,7 @@ public class LiftMonitor {
    * on any floor.
    */
   public synchronized int[] liftContinue() {
-
-    while (Arrays.stream(waitEntry).sum() == 0 &&
-        Arrays.stream(waitExit).sum() == 0) {
+    while (waitEntry.isEmpty() && waitExit.isEmpty()) {
       try {
         wait();
       } catch (InterruptedException e) {
@@ -115,7 +117,7 @@ public class LiftMonitor {
     }
 
     /** Stops the elevator to allow passengers to enter or exit */
-    while (waitEntry[floor] > 0 && load != 4 || waitExit[floor] > 0 ||
+    while (waitEntry.get(floor) > 0 && load != 4 || waitExit.get(floor) > 0 ||
         passengersEntering > 0 || passengersExiting > 0) {
       if (!door.isOpen()) {
         view.openDoors(floor);
@@ -160,16 +162,13 @@ public class LiftMonitor {
    * to enter or exit on floors either above or below the elevator
    */
   private void calculateDirection() {
-    if (Arrays.stream(waitEntry, floor, nfloors).sum() == 0 &&
-        Arrays.stream(waitExit, floor, nfloors).sum() == 0 && floor != 0) {
-      direction = Direction.DOWN;
-    } else if (Arrays.stream(waitEntry, 0, floor + 1).sum() == 0 &&
-        Arrays.stream(waitExit, 0, floor + 1).sum() == 0 && floor != 6) {
-      direction = Direction.UP;
-    } else if (floor == nfloors - 1) {
-      direction = Direction.DOWN;
-    } else if (floor == 0) {
-      direction = Direction.UP;
+    boolean noPassengersAbove = (waitEntry.totalAbove(floor) == 0 && waitExit.totalAbove(floor) == 0);
+    boolean noPassengersBelow = (waitEntry.totalBelow(floor) == 0 && waitExit.totalBelow(floor) == 0);
+
+    if (floor == 0 || noPassengersBelow) {
+      direction = Direction.UP; // Always go up if at ground floor or no passengers below
+    } else if (floor == nfloors - 1 || noPassengersAbove) {
+      direction = Direction.DOWN; // Always go down if at the top floor or no passengers above
     }
   }
 }

lift/src/lift/PassengerQueue.java

@@ -0,0 +1,44 @@
+package lift;
+
+import java.util.Arrays;
+
+public class PassengerQueue {
+    private int[] waitRecord;
+
+    public PassengerQueue(int nfloors) {
+        this.waitRecord = new int[nfloors];
+    }
+
+    public void inc(int floor) {
+        this.waitRecord[floor]++;
+    }
+
+    public void dec(int floor) {
+        this.waitRecord[floor]--;
+    }
+
+    public int get(int floor) {
+        return this.waitRecord[floor];
+    }
+
+    public void set(int floor, int value) {
+        this.waitRecord[floor] = value;
+    }
+
+    public int total() {
+        return Arrays.stream(this.waitRecord).sum();
+    }
+
+    public boolean isEmpty() {
+        return this.total() == 0;
+    }
+
+    public int totalBelow(int floor) {
+        return Arrays.stream(this.waitRecord).limit(floor).sum();
+    }
+
+    public int totalAbove(int floor) {
+        return Arrays.stream(this.waitRecord).skip(floor + 1).sum();
+    }
+}
+