本文共 1734 字，大约阅读时间需要 5 分钟。

import java.util.ArrayList; 2.import java.util.List; 3.import java.util.ListIterator; 4.import java.util.Random; 5.import java.util.RandomAccess; 6. 7.import org.junit.Test; 8./** 9. * Collections随机排序 10. * 11. */ 12.public class CollectionsShuffle { 13. 14. private static Random r; 15. private static final int SHUFFLE_THRESHOLD = 5; 16. 17. public static void shuffle(List<?> list) { 18. if (r == null) { 19. r = new Random(); 20. } 21. shuffle(list, r); 22. } 23. 24. public static void shuffle(List<?> list, Random rnd) { 25. int size = list.size(); 26. if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) { 27. for (int i = size; i > 1; i--) 28. swap(list, i - 1, rnd.nextInt(i)); 29. } else { 30. Object arr[] = list.toArray(); 31. 32. for (int i = size; i > 1; i--) 33. swap(arr, i - 1, rnd.nextInt(i)); 34. 35. ListIterator it = list.listIterator(); 36. for (int i = 0; i < arr.length; i++) { 37. it.next(); 38. it.set(arr[i]); 39. } 40. } 41. } 42. 43. public static void swap(List<?> list, int i, int j) { 44. final List l = list; 45. l.set(i, l.set(j, l.get(i))); 46. } 47. 48. private static void swap(Object[] arr, int i, int j) { 49. Object tmp = arr[i]; 50. arr[i] = arr[j]; 51. arr[j] = tmp; 52. } 53. 54. 55. //初始化List 56. public List<Integer> initList(){ 57. List<Integer> list = new ArrayList<Integer>(); 58. list.add(1); 59. list.add(2); 60. list.add(3); 61. list.add(4); 62. list.add(5); 63. list.add(6); 64. list.add(7); 65. list.add(8); 66. list.add(9); 67. return list; 68. } 69. 70. //测试Collections随机排序 71. @Test 72. public void testShuffle(){ 73. List<Integer> list = initList(); 74. shuffle(list, new Random()); 75. for (Integer value : list) { 76. System.out.println(value); 77. } 78. } 79. 80.}

转载地址：http://bknoi.baihongyu.com/