Add a QueueLinkedHashSet class

Change-Id: I17c38877fd69b7406cff9d2c56c26af33c3b9b10
Reviewed-on: http://gerrit.dmdirc.com/1629
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>

src/com/dmdirc/util/QueuedLinkedHashSet.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2006-2010 Chris Smith, Shane Mc Cormack, Gregory Holmes
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package com.dmdirc.util;
+
+import java.util.Iterator;
+import java.util.LinkedHashSet;
+import java.util.NoSuchElementException;
+import java.util.Queue;
+
+/**
+ * A LinkedHashSet with a Queue implementation added, also supports readding
+ * unique items to the head of the queue.
+ *
+ * @param <E> the type of elements held in this collection
+ */
+public class QueuedLinkedHashSet<E> extends LinkedHashSet<E>
+        implements Queue<E> {
+
+    /** {@inheritDoc} */
+    @Override
+    public boolean offer(final E e) {
+        return add(e);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public E remove() {
+        if (isEmpty()) {
+            throw new NoSuchElementException("Queue is empty.");
+        }
+        return poll();
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public E poll() {
+        final E object = peek();
+        if (object != null) {
+            remove(object);
+        }
+        return object;
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public E element() {
+        if (isEmpty()) {
+            throw new NoSuchElementException("Queue is empty.");
+        }
+        return peek();
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public E peek() {
+        if (isEmpty()) {
+            return null;
+        }
+        final Iterator<E> iterator = iterator();
+        E object = null;
+        while (iterator.hasNext()) {
+            object = iterator.next();
+        }
+        return object;
+    }
+
+    /**
+     * Offers an item to this queue, if the item exists in the queue it removes
+     * it and re-adds it to the queue.
+     *
+     * @param e Object to add
+     *
+     * @return true iif the item was added
+     */
+    public boolean offerAndMove(final E e) {
+        if (contains(e)) {
+            remove(e);
+        }
+        return offer(e);
+    }
+}