Java - The TreeMap Class
The TreeMap class implements the Map interface by using a tree. A TreeMap provides an efficient means of storing key/value pairs in sorted order, and allows rapid retrieval.
You should note that, unlike a hash map, a tree map guarantees that its elements will be sorted in an ascending key order.
Following is the list of the constructors supported by the TreeMap class.
| Sr.No. | Constructors & Description |
|---|---|
| 1 | TreeMap( ) This constructor constructs an empty tree map that will be sorted using the natural order of its keys. |
| 2 | TreeMap(Comparator comp) This constructor constructs an empty tree-based map that will be sorted using the Comparator comp. |
| 3 | TreeMap(Map m) This constructor initializes a tree map with the entries from m, which will be sorted using the natural order of the keys. |
| 4 | TreeMap(SortedMap sm) This constructor initializes a tree map with the entries from the SortedMap sm, which will be sorted in the same order as sm. |
Apart from the methods inherited from its parent classes, TreeMap defines the following methods −
| Sr.No. | Method & Description |
|---|---|
| 1 | void clear() Removes all mappings from this TreeMap. |
| 2 | Object clone() Returns a shallow copy of this TreeMap instance. |
| 3 | Comparator comparator() Returns the comparator used to order this map, or null if this map uses its keys' natural order. |
| 4 | boolean containsKey(Object key) Returns true if this map contains a mapping for the specified key. |
| 5 | boolean containsValue(Object value) Returns true if this map maps one or more keys to the specified value. |
| 6 | Set entrySet() Returns a set view of the mappings contained in this map. |
| 7 | Object firstKey() Returns the first (lowest) key currently in this sorted map. |
| 8 | Object get(Object key) Returns the value to which this map maps the specified key. |
| 9 | SortedMap headMap(Object toKey) Returns a view of the portion of this map whose keys are strictly less than toKey. |
| 10 | Set keySet() Returns a Set view of the keys contained in this map. |
| 11 | Object lastKey() Returns the last (highest) key currently in this sorted map. |
| 12 | Object put(Object key, Object value) Associates the specified value with the specified key in this map. |
| 13 | void putAll(Map map) Copies all of the mappings from the specified map to this map. |
| 14 | Object remove(Object key) Removes the mapping for this key from this TreeMap if present. |
| 15 | int size() Returns the number of key-value mappings in this map. |
| 16 | SortedMap subMap(Object fromKey, Object toKey) Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive. |
| 17 | SortedMap tailMap(Object fromKey) Returns a view of the portion of this map whose keys are greater than or equal to fromKey. |
| 18 | Collection values() Returns a collection view of the values contained in this map. |
Example
The following program illustrates several of the methods supported by this collection −
import java.util.*;
public class TreeMapDemo {
public static void main(String args[]) {
// Create a hash map
TreeMap tm = new TreeMap();
// Put elements to the map
tm.put("Zara", new Double(3434.34));
tm.put("Mahnaz", new Double(123.22));
tm.put("Ayan", new Double(1378.00));
tm.put("Daisy", new Double(99.22));
tm.put("Qadir", new Double(-19.08));
// Get a set of the entries
Set set = tm.entrySet();
// Get an iterator
Iterator i = set.iterator();
// Display elements
while(i.hasNext()) {
Map.Entry me = (Map.Entry)i.next();
System.out.print(me.getKey() + ": ");
System.out.println(me.getValue());
}
System.out.println();
// Deposit 1000 into Zara's account
double balance = ((Double)tm.get("Zara")).doubleValue();
tm.put("Zara", new Double(balance + 1000));
System.out.println("Zara's new balance: " + tm.get("Zara"));
}
}
This will produce the following result −
Output
Ayan: 1378.0 Daisy: 99.22 Mahnaz: 123.22 Qadir: -19.08 Zara: 3434.34 Zara's new balance: 4434.34