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
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