Java.util.TreeMap implements SortedMap interface and provides an efficient way to storing key-value pairs in sorted order. TreeMap implements the NavigableMap interface and extends AbstractMap class.
Points to Remember
- TreeMap uses data structure as a red-black tree.
- TreeMap contains values based on the key.
- TreeMap contains only unique elements.
- TreeMap cannot have a null key but can have multiple null values.
- TreeMap is not synchronized.
- TreeMap maintains an ascending order.
TreeMap Declaration
public class TreeMap extends AbstractMap implements NavigableMap, Serializable,Cloneable- K: Represent as key in Map
- V: Represent as value with respect to K.
See Also:
- Java: How HashMap works?
- Java: HashTable Class Methods and Examples
- Java: HashMap Class Methods and Examples
- Java: Difference between HashMap and Hashtable
What is the difference between HashMap and TreeMap?
| HashMap | TreeMap |
| HashMap can contain one null key. | TreeMap cannot contain any null key. |
| HashMap maintains no order. | TreeMap maintains an ascending order. |
Constructors of TreeMap
| Constructor | Description |
| TreeMap() | This constructor uses to create an empty treemap that will be sorted using the natural order of its key. |
| TreeMap(Comparator comparator) | This constructor uses to an empty tree-based map that will be sorted using the comparator comp. |
| TreeMap(Map m) | It is used to initialize a treemap with the entries from m, which will be sorted using the natural order of the keys. |
| TreeMap(SortedMap m) | This constructor uses to initialize a treemap with the entries from the SortedMap sm, which will be sorted in the same order as sm. |
Methods of TreeMap
| Method | Description |
| Map.Entry ceilingEntry(K key) | It returns the key-value pair having the least key, greater than or equal to the specified key, or null if there is no such key. |
| K ceilingKey(K key) | It returns the least key, greater than the specified key or null if there is no such key. |
| void clear() | It removes all the key-value pairs from a map. |
| Object clone() | It returns a shallow copy of TreeMap instance. |
| Comparator comparator() | It returns the comparator that arranges the key in order, or null if the map uses the natural ordering. |
| NavigableSet descendingKeySet() | This method returns a reverse order NavigableSet view of the keys contained in the map. |
| NavigableMap descendingMap() | It returns the specified key-value pairs in descending order. |
| Map.Entry firstEntry() | It returns the key-value pair having the least key. |
| Map.Entry floorEntry(K key) | It returns the greatest key, less than or equal to the specified key, or null if there is no such key. |
| void forEach(BiConsumer action) | It performs the mention action for each entry in the map until all entries processed or the action throws an exception. |
| SortedMap headMap(K toKey) | It returns the key-value pairs whose keys are strictly less than toKey. |
| NavigableMap headMap(K toKey, boolean inclusive) | It returns the key-value pairs whose keys are less than (or equal to if inclusive is true) toKey. |
| Map.Entry higherEntry(K key) | It returns the least key strictly greater than the given key, or null if there is no such key. |
| K higherKey(K key) | It is used to return true if map contains a mapping for the specified key. |
| Set keySet() | It returns the set of keys exist in the map. |
| Map.Entry lastEntry() | It returns the key-value pair having the greatest key, or null if there is no such key. |
| Map.Entry lowerEntry(K key) | It returns a key and value mapping associated with the greatest key less than the given key or null if there is no such key. |
| K lowerKey(K key) | It returns from map the greatest key strictly less than the given key, or null if there is no such key. |
| NavigableSet navigableKeySet() | It returns a NavigableSet view of the keys contains in this map. |
| Map.Entry pollFirstEntry() | It removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty. |
| Map.Entry pollLastEntry() | It removes and returns a key and value mapping associated with the greatest key in this map, or null if the map is empty. |
| V put(K key, V value) | It inserts the specified value with respect to key in the map. |
| void putAll(Map map) | It is used to copy all the key-value pair from one map to another map. |
| V replace(K key, V value) | It replaces the value with respect to key. |
| boolean replace(K key, V oldValue, V newValue) | It replaces the old value with the new value with respect to key. |
| void replaceAll(BiFunction function) | It replaces each entry’s value with the result of invoking the mentioned function on all entries have been processed or the function throw an exception. |
| NavigableMap subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) | It returns key and value pairs whose keys match with in range fromKey to toKey. |
| SortedMap subMap(K fromKey, K toKey) | It returns key and value pairs whose keys range match fromKey, inclusive, to toKey, exclusive. |
| SortedMap tailMap(K fromKey) | It returns key and value pairs whose keys are greater than or equal to fromKey. |
| NavigableMap tailMap(K fromKey, boolean inclusive) | It returns key and value pairs whose keys are greater than (o equal to, if inclusive is true) fromKey. |
| boolean containsKey(Object key) | It returns true if the map contains a mapping with respect to key. |
| boolean containsValue(Object value) | It returns true if the map find one or more keys to the specified value. |
| K firstKey() | It is used to return the first find lowest key currently in this sorted map. |
| V get(Object key) | It is used to return the value to which the map maps the specified key. |
| K lastKey() | It is used to return the last highest key currently in the sorted map. |
| V remove(Object key) | It removes the key and value pair of the specified key from the map. |
| Set entrySet() | It returns a set of the mappings contained in the map. |
| int size() | It returns the number of key-value pairs that exists in the hashtable. |
| Collection values() | It returns a collection of values contained in the map. |
TreeMap Example : insert and traverse elements
import java.util.Map;
import java.util.TreeMap;
class TreeMapExample1{
public static void main(String args[]){
TreeMap<Integer,String> map=new TreeMap<Integer,String>();
map.put(20,"Anuj");
map.put(22,"Ravi");
map.put(21,"Virendra");
map.put(23,"Raghav");
for(Map.Entry m:map.entrySet()){
System.out.println(m.getKey()+" "+m.getValue());
}
}
}
Output :
20 Anuj
21 Virendra
22 Ravi
23 Raghav
TreeMap Example : remove() elements
import java.util.*;
public class TreeMapExample2 {
public static void main(String args[]) {
TreeMap<Integer, String> map = new TreeMap<Integer, String>();
map.put(20, "Anuj");
map.put(22, "Ravi");
map.put(21, "Virendra");
map.put(23, "Raghav");
System.out.println("\nBefore invoking remove() method");
for (Map.Entry m : map.entrySet()) {
System.out.println(m.getKey() + " " + m.getValue());
}
map.remove(22);
System.out.println("\nAfter invoking remove() method");
for (Map.Entry m : map.entrySet()) {
System.out.println(m.getKey() + " " + m.getValue());
}
}
}
Output :
Before invoking remove() method
20 Anuj
21 Virendra
22 Ravi
23 Raghav
After invoking remove() method
20 Anuj
21 Virendra
23 Raghav
Treemap Example : with NavigableMap
import java.util.*;
import java.util.NavigableMap;
import java.util.TreeMap;
class TreeMapExample3 {
public static void main(String args[]) {
NavigableMap<Integer, String> map = new TreeMap<Integer, String>();
map.put(20, "Anuj");
map.put(22, "Ravi");
map.put(21, "Virendra");
map.put(23, "Raghav");
// Maintains descending order
System.out.println("\ndescendingMap: " + map.descendingMap());
// Returns key-value pairs whose keys are less than or equal to the
// specified key.
System.out.println("\nheadMap: " + map.headMap(22, true));
// Returns key-value pairs whose keys are greater than or equal to the
// specified key.
System.out.println("\ntailMap: " + map.tailMap(22, true));
// Returns key-value pairs exists in between the specified key.
System.out.println("\nsubMap: " + map.subMap(20, false, 22, true));
}
}
Output :
descendingMap: {23=Raghav, 22=Ravi, 21=Virendra, 20=Anuj}
headMap: {20=Anuj, 21=Virendra, 22=Ravi}
tailMap: {22=Ravi, 23=Raghav}
subMap: {21=Virendra, 22=Ravi}
TreeMap Example : SortedMap()
import java.util.*;
import java.util.SortedMap;
import java.util.TreeMap;
class TreeMapExample4 {
public static void main(String args[]) {
SortedMap<Integer, String> map = new TreeMap<Integer, String>();
map.put(20, "Anuj");
map.put(22, "Ravi");
map.put(21, "Virendra");
map.put(23, "Raghav");
// Returns key-value pairs whose keys are less than the specified key.
System.out.println("\nheadMap: " + map.headMap(22));
// Returns key-value pairs whose keys are greater than or equal to the
// specified key.
System.out.println("\ntailMap: " + map.tailMap(22));
// Returns key-value pairs exists in between the specified key.
System.out.println("\nsubMap: " + map.subMap(20, 22));
}
}
Output :
headMap: {20=Anuj, 21=Virendra}
tailMap: {22=Ravi, 23=Raghav}
subMap: {20=Anuj, 21=Virendra}
TreeMap Example : with objects
import java.util.*;
class Magzine{
int id;
String name,author,publisher;
int quantity;
public Magzine(int id, String name, String author, String publisher, int quantity) {
this.id = id;
this.name = name;
this.author = author;
this.publisher = publisher;
this.quantity = quantity;
}
}
import java.util.Map;
import java.util.TreeMap;
public class HashtableExampleWithObjects {
public static void main(String[] args) {
// Creating map of Magzine
Map<Integer, Magzine> table = new TreeMap<Integer, Magzine>();
// Creating Magzines
Magzine m1 = new Magzine(21, "The Sun", "Sy Sunfranchy", "The Sun Company", 8);
Magzine m2 = new Magzine(22, "Glimmer Trains", "Unknown", "Glimmer Train Press", 4);
Magzine m3 = new Magzine(23, "Crazy horse", "Brett Lot", "College of Charleston", 6);
// Adding magzine to map
table.put(1, m1);
table.put(2, m2);
table.put(3, m3);
// Traversing map
for (Map.Entry<Integer, Magzine> entry : table.entrySet()) {
int key = entry.getKey();
Magzine m = entry.getValue();
System.out.println("\nId: "+key + " Details:");
System.out.println(m.id + " " + m.name + " " + m.author + " " + m.publisher + " " + m.quantity);
}
}
}
Output :
Id: 1 Details:
21 The Sun Sy Sunfranchy The Sun Company 8
Id: 2 Details:
22 Glimmer Trains Unknown Glimmer Train Press 4
Id: 3 Details:
23 Crazy horse Brett Lot College of Charleston 6
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