CircularQueue and test

scala/src/main/scala/ch09_queue/CircularQueue.scala

@@ -0,0 +1,29 @@
+package ch09_queue
+
+import scala.reflect.ClassTag
+
+class CircularQueue[T: ClassTag](capacity: Int) extends DemoQueue[T] {
+
+  var items: Array[T] = new Array[T](capacity)
+  var head = 0
+  var tail = 0
+
+
+  override def enqueue(data: T): Unit = {
+    require((tail + 1) % capacity != head, "queue is full")
+    items(tail) = data
+    tail = (tail + 1) % capacity
+    size += 1
+  }
+
+  override def dequeue(): Option[T] = {
+    if (head == tail) {
+      None
+    } else {
+      size -= 1
+      val result = Some(items(head))
+      head = (head + 1) % capacity
+      result
+    }
+  }
+}

scala/src/test/scala/ch09_queue/CircularQueueTest.scala

@@ -0,0 +1,6 @@
+package ch09_queue
+
+class CircularQueueTest extends DemoQueueTest {
+
+  override def getInstance(): DemoQueue[Int] = new CircularQueue[Int](15)
+}