java.util.Collections 集合帮助类

演示样例程序(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 
      
     

super T>> void sort(List<T> 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
        
       
      
     

super T>> 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 <T> boolean replaceAll(List<T> 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());    }
         
        
       
      
     

比較

@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  无加入方法        List
       
         emptyList = Collections.emptyList();        //返回一个仅仅包括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改动视图。        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