java.util.collections是单实例类吗

发布网友发布时间：2022-04-14 18:00

共2个回答

懂视网时间：2022-04-14 22:22

java.util.Collections 集合帮助类示例程序(JUnit演示) 排序 @Test public void testSort() { ListInteger demoList = new ArrayListInteger(Arrays.asList(3, 2, 1)); assertEquals(3, demoList.get(0).intValue()); //public static T extends Comparable

java.util.Collections 集合帮助类

示例程序(JUnit演示)

排序

 @Test
 public void testSort() {
 List demoList = new ArrayList(Arrays.asList(3, 2, 1));
 assertEquals(3, demoList.get(0).intValue());

 //public static > void sort(List list)
 Collections.sort(demoList);

 assertEquals(1, demoList.get(0).intValue());

 //public static void shuffle(List list) // 随机排序
 //public static void reverse(List list) // 反序  
 }



查找
 @Test
 public void testBinarySearch() {
 List demoList = new ArrayList(Arrays.asList(3, 2, 1));
 //必须先排序
 Collections.sort(demoList);
 assertEquals(1, demoList.get(0).intValue());

 //二分查找位置
 //public static  int binarySearch(List> list, T key)
 assertEquals(0, Collections.binarySearch(demoList, 1));

 //public static int indexOfSubList(List source, List target)
 // public static int lastIndexOfSubList(List source, List target)
 }


置换
 @Test
 public void testSwap() {
 List demoList = new ArrayList(Arrays.asList(3, 2, 1));

 //public static void swap(List list, int i, int j)
 Collections.swap(demoList, 0, 2);
 assertEquals(1, demoList.get(0).intValue());
 //public static void rotate(List list, int distance) //指定距离轮换
 //public static  boolean replaceAll(List list, T oldVal, T newVal) //指定替换
 }


拷贝
 @Test
 public void testCopy() {
 List demoList = new ArrayList(Arrays.asList(3, 2, 1));

 //public static  void copy(List dest, List src)
 //注意目的List的size最少要等于src的size
 List copyList = new ArrayList(Arrays.asList(1, 2, 3));
 Collections.copy(copyList, demoList);
 assertEquals(3, copyList.size());
 assertEquals(3, copyList.get(0).intValue());

 copyList.add(4);
 assertEquals(3, demoList.size());
 }


比较
 @Test
 public void testCompary() {
 List demoList = new ArrayList(Arrays.asList(3, 2, 1));
 assertEquals(1, Collections.min(demoList).intValue());
 assertEquals(3, Collections.max(demoList).intValue());

 List compareList = new ArrayList(Arrays.asList(5, 6, 7));
 //Returns true if the two specified collections have no elements in common
 assertTrue(Collections.disjoint(demoList, compareList));
 }


创造不同的集合
 @SuppressWarnings("unused")
 @Test
 public void testCreate() {
 List demoList = new ArrayList(Arrays.asList(3, 2, 1));

 //空对象 size=0 无添加方法
 List emptyList = Collections.emptyList();

 //返回一个只包含指定对象的不可变列表。
 List singletonList = Collections.singletonList(1);

 //返回指定列表的一个动态类型安全视图。
 List checkedList = Collections.checkedList(demoList, Integer.class);

 //返回指定列表的不可修改视图。
 List unmodifiableList = Collections.unmodifiableList(demoList);

 //返回指定列表支持的同步（线程安全的）列表。
 List synchronizedList = Collections.synchronizedList(demoList);

 synchronized (synchronizedList) {
  Iterator i = synchronizedList.iterator(); // Must be in synchronized block
  while (i.hasNext())
  i.next();
 }

 //map set sortedMap sortedSet
 }


环境 jdk1.6 window7 junit4						 




                                        
                        
                        热心网友
                        时间：2022-04-14 19:30
                    
                    ava.util.Collections类专门由操作上或返回集合的静态方法。以下是关于集合的要点：
它包含在collection上，“包装”，它会返回一个新的集合由一个指定的集合操作支持多态算法。
这个类的方法都抛出NullPointerException如果提供给他们的集合或类对象为null。