first commit

java/queue/ArrayQueue.java

@@ -0,0 +1,90 @@
+package queue;
+
+/**
+ * @author Doschennikov Nikita (me@fymio.us)
+ */
+public class ArrayQueue extends AbstractQueue {
+
+    private Object[] queue;
+    private int head;
+
+    public ArrayQueue() {
+        queue = new Object[4];
+        head = 0;
+    }
+
+    @Override
+    public void enqueue(Object element) {
+        assert element != null : "Element must not be null";
+        ensureCapacity();
+        queue[(head + size) % queue.length] = element;
+        size++;
+    }
+
+    @Override
+    public void push(Object element) {
+        assert element != null : "Element must not be null";
+        ensureCapacity();
+        head = (head - 1 + queue.length) % queue.length;
+        queue[head] = element;
+        size++;
+    }
+
+    @Override
+    public Object element() {
+        assert size > 0 : "Queue is empty";
+        return queue[head];
+    }
+
+    @Override
+    public Object peek() {
+        assert size > 0 : "Queue is empty";
+        return queue[(head + size - 1) % queue.length];
+    }
+
+    @Override
+    public Object dequeue() {
+        assert size > 0 : "Queue is empty";
+        Object result = queue[head];
+        queue[head] = null;
+        head = (head + 1) % queue.length;
+        size--;
+        return result;
+    }
+
+    @Override
+    public Object remove() {
+        assert size > 0 : "Queue is empty";
+        int tail = (head + size - 1) % queue.length;
+        Object result = queue[tail];
+        queue[tail] = null;
+        size--;
+        return result;
+    }
+
+    @Override
+    protected Object get(int i) {
+        return queue[(head + i) % queue.length];
+    }
+
+    @Override
+    protected void clearImpl() {
+        queue = new Object[4];
+        head = 0;
+    }
+
+    @Override
+    protected AbstractQueue createEmpty() {
+        return new ArrayQueue();
+    }
+
+    private void ensureCapacity() {
+        if (size < queue.length) return;
+        Object[] newQueue = new Object[queue.length * 2];
+        for (int i = 0; i < size; i++) {
+            newQueue[i] = queue[(head + i) % queue.length];
+        }
+        queue = newQueue;
+        head = 0;
+    }
+}