·
TreeMap object is sorted according to the
natural ordering of its keys if created using default constructor( new
TreeMap()), or by a Comparator if TreeMap object is created by passing
Comparator to constructor ( new TreeMap(comparator))
·
Provides guaranteed log(n) time cost for
the containsKey, get, put and remove operations.
·
If TreeMap object is created using
default constructor then all keys inserted into the map must implement the
Comparable interface else you will get exception while adding key-values to
TreeMap instance.
java.lang.ClassCastException: xxxx
cannot be cast to java.lang.Comparable
·
All keys inserted into the map must
be of same type. e.g. you can’t add integer as a key into a map whose keys are
String
·
Does not allows null keys, valuse can
be null.
·
A TreeMap is not synchronized. Means its
methods are not synchronized.
·
In multi-threaded environment, to
prevent accidental unsynchronized access to the TreeMap that can modify it,
wrap TreeMap using Collections.synchronizedSortedMap method
SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));
·
The iterators returned by this
class's iterator methods are fail-fast. If the map is modified at any time
after the iterator is created, in any way except through the iterator's own
remove method, the iterator will throw a ConcurrentModificationException.
·
Fail-fast iterators throw
ConcurrentModificationException on a best-effort basis. But one must not write
program that depends on this behaviour.
·
There are multiple ways to iterate
over TreeMap
//create TreeMap instance
TreeMap treeMap = new TreeMap();
//add key value pairs to TreeMap
treeMap.put("1","A");
treeMap.put("2","B");
treeMap.put("3","C");
1. Iterator using
Collection values() - only iterate TreeMap's values
Collection c = treeMap.values();
Iterator itr = c.iterator();
while(itr.hasNext())
System.out.println(itr.next());
2. Iterator using
entrySet() - iterate TreeMap's keys and values in map form
for (Map.Entry entry : treeMap.entrySet()) {
V value = entry.getValue();
K key = entry.getKey();
}
3. Iterator using
keySet() - iterate TreeMap's keys which can be used to get values
Set keys = map.keySet();
for (Iterator i = keys.iterator(); i.hasNext();) {
Integer key = (Integer) i.next();
String value = (String) map.get(key);
}
Note : If the TreeMap is modified while an iteration over the collection/set
is in progress (except through the iterator's own remove operation, the results
of the iteration are undefined.The collection/set supports element removal,
which removes the corresponding mapping from the map, via the Iterator.remove,
Set.remove, removeAll, retainAll, and clear operations. It does not
support the add or addAll operations.
·
put(K key, V value) method returns
previous value associated with key, or null if there was no mapping for key. If
the map previously contained a mapping for the key, the old value is replaced
with new value.
