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QueuedLinkedHashSet.java 2.9KB

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  1. /*
  2. * Copyright (c) 2006-2010 Chris Smith, Shane Mc Cormack, Gregory Holmes
  3. *
  4. * Permission is hereby granted, free of charge, to any person obtaining a copy
  5. * of this software and associated documentation files (the "Software"), to deal
  6. * in the Software without restriction, including without limitation the rights
  7. * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  8. * copies of the Software, and to permit persons to whom the Software is
  9. * furnished to do so, subject to the following conditions:
  10. *
  11. * The above copyright notice and this permission notice shall be included in
  12. * all copies or substantial portions of the Software.
  13. *
  14. * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  15. * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  16. * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  17. * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  18. * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  19. * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  20. * SOFTWARE.
  21. */
  22. package com.dmdirc.util;
  23. import java.util.Iterator;
  24. import java.util.LinkedHashSet;
  25. import java.util.NoSuchElementException;
  26. import java.util.Queue;
  27. /**
  28. * A LinkedHashSet with a Queue implementation added, also supports readding
  29. * unique items to the head of the queue.
  30. *
  31. * @param <E> the type of elements held in this collection
  32. */
  33. public class QueuedLinkedHashSet<E> extends LinkedHashSet<E>
  34. implements Queue<E> {
  35. /** {@inheritDoc} */
  36. @Override
  37. public boolean offer(final E e) {
  38. return add(e);
  39. }
  40. /** {@inheritDoc} */
  41. @Override
  42. public E remove() {
  43. if (isEmpty()) {
  44. throw new NoSuchElementException("Queue is empty.");
  45. }
  46. return poll();
  47. }
  48. /** {@inheritDoc} */
  49. @Override
  50. public E poll() {
  51. final E object = peek();
  52. if (object != null) {
  53. remove(object);
  54. }
  55. return object;
  56. }
  57. /** {@inheritDoc} */
  58. @Override
  59. public E element() {
  60. if (isEmpty()) {
  61. throw new NoSuchElementException("Queue is empty.");
  62. }
  63. return peek();
  64. }
  65. /** {@inheritDoc} */
  66. @Override
  67. public E peek() {
  68. if (isEmpty()) {
  69. return null;
  70. }
  71. final Iterator<E> iterator = iterator();
  72. E object = null;
  73. while (iterator.hasNext()) {
  74. object = iterator.next();
  75. }
  76. return object;
  77. }
  78. /**
  79. * Offers an item to this queue, if the item exists in the queue it removes
  80. * it and re-adds it to the queue.
  81. *
  82. * @param e Object to add
  83. *
  84. * @return true iif the item was added
  85. */
  86. public boolean offerAndMove(final E e) {
  87. if (contains(e)) {
  88. remove(e);
  89. }
  90. return offer(e);
  91. }
  92. }