first commit

java/queue/LinkedQueue.java

@@ -0,0 +1,114 @@
+package queue;
+
+/**
+ * @author Doschennikov Nikita (me@fymio.us)
+ */
+public class LinkedQueue extends AbstractQueue {
+
+    private Node head;
+    private Node tail;
+
+    private static class Node {
+
+        Object value;
+        Node next;
+        Node prev;
+
+        Node(Object value) {
+            this.value = value;
+        }
+    }
+
+    public LinkedQueue() {
+        head = null;
+        tail = null;
+    }
+
+    @Override
+    public void enqueue(Object element) {
+        assert element != null : "Element must not be null";
+        Node node = new Node(element);
+        if (tail == null) {
+            head = tail = node;
+        } else {
+            node.prev = tail;
+            tail.next = node;
+            tail = node;
+        }
+        size++;
+    }
+
+    @Override
+    public void push(Object element) {
+        assert element != null : "Element must not be null";
+        Node node = new Node(element);
+        if (head == null) {
+            head = tail = node;
+        } else {
+            node.next = head;
+            head.prev = node;
+            head = node;
+        }
+        size++;
+    }
+
+    @Override
+    public Object element() {
+        assert size > 0 : "Queue is empty";
+        return head.value;
+    }
+
+    @Override
+    public Object peek() {
+        assert size > 0 : "Queue is empty";
+        return tail.value;
+    }
+
+    @Override
+    public Object dequeue() {
+        assert size > 0 : "Queue is empty";
+        Object result = head.value;
+        head = head.next;
+        if (head != null) {
+            head.prev = null;
+        } else {
+            tail = null;
+        }
+        size--;
+        return result;
+    }
+
+    @Override
+    public Object remove() {
+        assert size > 0 : "Queue is empty";
+        Object result = tail.value;
+        tail = tail.prev;
+        if (tail != null) {
+            tail.next = null;
+        } else {
+            head = null;
+        }
+        size--;
+        return result;
+    }
+
+    @Override
+    protected Object get(int i) {
+        Node cur = head;
+        for (int j = 0; j < i; j++) {
+            cur = cur.next;
+        }
+        return cur.value;
+    }
+
+    @Override
+    protected void clearImpl() {
+        head = null;
+        tail = null;
+    }
+
+    @Override
+    protected AbstractQueue createEmpty() {
+        return new LinkedQueue();
+    }
+}