TreeMap
基于红黑树的NavigableMap实现.元素根据Key的自然顺序排序,或者是根据构造函数传入的Comparator排序.
该集合对containsKey, get, put and remove的操作保证log(n)的时间复杂度.算法实现改编自Cormen, Leiserson, and Rivest的<<算法导论>>(Introduction to Algorithms).
注意为了保证正确实现有序Map,Comparable 和 Comparator 需要与 equals 保持一致性的语义.
当且仅当c.compare(e1, e2)==0具有与e1.equals(e2)相同的布尔值时, 比较器c对一组元素S的排序与equals一致.
实现是非线程安全的,若需要多线程访问,要使用同步包装器或者同步容器.
迭代器方法遵循集合的快速失败语义:迭代器创建之后的任何其他修改将导致ConcurrentModificationException异常.
API Example
元素查找之 Contains
TreeMap<Integer, Object> treeMap = new TreeMap<>();
treeMap.put(1, 1);
treeMap.put(2, 2);
//log(n)时间复杂度
assertTrue(treeMap.containsKey(1));
//线性时间复杂度
assertTrue(treeMap.containsValue(1));
元素查找之 Get
TreeMap<Integer, Object> treeMap = new TreeMap<>();
treeMap.put(1, 1);
treeMap.put(2, 2);
//log(n)时间复杂度
Object value = treeMap.get(2);
assertEquals(value, 2);
元素查找之最大最小
TreeMap<Integer, Object> treeMap = new TreeMap<>();
treeMap.put(1, 1);
treeMap.put(2, 2);
treeMap.put(3, 3);
//log(n)时间复杂度
//最小值
assertEquals(treeMap.firstKey(), 1);
//删除并返回最小值
Map.Entry<Integer, Object> firstEntry = treeMap.pollFirstEntry();
assertEquals(firstEntry, "1=1");
//最大值
assertEquals(treeMap.lastKey(), 3);
//删除并返回最大值
Map.Entry<Integer, Object> lastEntry = treeMap.pollLastEntry();
assertEquals(lastEntry, "3=3");
元素查找之范围比较
TreeMap<Integer, Object> treeMap = new TreeMap<>();
treeMap.put(1, 1);
treeMap.put(3, 3);
treeMap.put(5, 5);
treeMap.put(7, 7);
treeMap.put(9, 9);
//集合中小于等于指定key的最大key
Integer floorKey = treeMap.floorKey(3);
assertEquals(floorKey, 3);
//集合中小于等于指定key的最大key对应的映射
Map.Entry<Integer, Object> floorEntry = treeMap.floorEntry(3);
assertEquals(floorEntry, "3=3");
//集合中大于等于指定key的最小key
Integer ceilingKey = treeMap.ceilingKey(5);
assertEquals(ceilingKey, 5);
//集合中大于等于指定key的最小key对应的映射
Map.Entry<Integer, Object> ceilingEntry = treeMap.ceilingEntry(5);
assertEquals(ceilingEntry, "5=5");
//集合中小于指定key的最大key
Integer lowerKey = treeMap.lowerKey(3);
assertEquals(lowerKey, 1);
//集合中小于指定key的最大key的映射
Map.Entry<Integer, Object> lowerEntry = treeMap.lowerEntry(3);
assertEquals(lowerEntry, "1=1");
//集合中大于指定key的最小key
Integer higherKey = treeMap.higherKey(5);
assertEquals(higherKey, 7);
//集合中大于指定key的最小key的映射
Map.Entry<Integer, Object> higherEntry = treeMap.higherEntry(5);
assertEquals(higherEntry, "7=7");
元素查找之范围比较视图 Map
TreeMap<Integer, Object> treeMap = new TreeMap<>();
treeMap.put(1, 1);
treeMap.put(3, 3);
treeMap.put(5, 5);
treeMap.put(7, 7);
treeMap.put(9, 9);
//[,5) 返回treeMap中严格小于toKey的视图map,视图map共享底层数据
SortedMap<Integer, Object> headMap = treeMap.headMap(5);
assertEquals(headMap, "{1=1, 3=3}");
//[5,) 返回treeMap中大于等于fromKey的视图map,视图map共享底层数据
SortedMap<Integer, Object> fromMap = treeMap.tailMap(5);
assertEquals(fromMap, "{5=5, 7=7, 9=9}");
//[2,9) 返回treeMap中大于等于fromKey且小于toKey的视图map,视图map共享底层数据
SortedMap<Integer, Object> subMap = treeMap.subMap(2, 9);
assertEquals(subMap, "{3=3, 5=5, 7=7}");
构造函数之指定 Map集合
Map<Integer, Object> src = new HashMap<>();
src.put(1, 1);
src.put(2, 2);
//构造时间复杂度为n*log(n)
TreeMap<Integer, Object> treeMap = new TreeMap<>(src);
assertEquals(treeMap, "{1=1, 2=2}");
构造函数之指定有序 Map集合
SortedMap<Integer, Object> src = new TreeMap<>();
src.put(1, 1);
src.put(2, 2);
//构造时间复杂度为线性时间,直接使用src的顺序和比较器
TreeMap<Integer, Object> treeMap = new TreeMap<>(src);
assertEquals(treeMap, "{1=1, 2=2}");
构造函数之指定比较器
//整数逆序的比较器
TreeMap<Integer, Object> treeMap = new TreeMap<>((o1, o2) -> o2 - o1);
treeMap.put(1, 1);
treeMap.put(2, 2);
assertEquals(treeMap, "{2=2, 1=1}");
构造函数之空 Map
TreeMap<Integer, Object> treeMap = new TreeMap<>();
assertEquals(treeMap, "{}");
集合元素顺序逆转的视图 Map
TreeMap<Integer, Object> treeMap = new TreeMap<>();
treeMap.put(1, 1);
treeMap.put(3, 3);
treeMap.put(5, 5);
assertEquals(treeMap, "{1=1, 3=3, 5=5}");
NavigableMap<Integer, Object> descendingMap = treeMap.descendingMap();
assertEquals(descendingMap, "{5=5, 3=3, 1=1}");
NavigableSet<Integer> descendingKeySet = treeMap.descendingKeySet();
assertEquals(descendingKeySet, "[5, 3, 1]");