TreeMap in java

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TreeMap:

TreeMap extends AbstractMap class and implements the NavigableMap interface. It contains the elements in key-value pair form. It maintains ascending order for its elements. It is not allowed duplicate keys.

Note:

  • A TreeMap can have only one null key but can have multiple null values.
  • It is non-synchronized.

TreeMap class declaration:

public class TreeMap<K,V> extends AbstractMap<K,V> implements NavigableMap<K,V>, Cloneable, Serializable

Where:

  • K: The type of keys maintained by the TreeMap.
  • V: The type of mapped values.

TreeMap class Constructors:

Constructor Description
TreeMap() It will create an empty treemap that will be sorted using the natural order of its key.
TreeMap(Comparator<? super K> comparator) It will create an empty tree-based map that will be sorted using the comparator comp.
TreeMap(Map<? extends K,? extends V> m) It will create and initialize a treemap with the entries from m, which will be sorted using the natural order of the keys.
TreeMap(SortedMap<K,? extends V> m) It will create and initialize a treemap with the entries from the SortedMap m, which will be sorted in the same order as m.

TreeMap class Methods:

Method Description
Map.Entry<K,V> ceilingEntry(K key) It will return 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 will return the least key, greater than the specified key or null if there is no such key.
void clear() It will eliminate or delete all the key-value pairs from a map.
Object clone() It will return a shallow copy of TreeMap instance.
Comparator<? super K> comparator() It will return the comparator that arranges the key in order, or null if the map uses the natural ordering.
NavigableSet<K> descendingKeySet() It will return a reverse order NavigableSet view of the keys contained in the map.
NavigableMap<K,V> descendingMap() It will return the specified key-value pairs in descending order.
Map.Entry firstEntry() It will return the key-value pair having the least key.
Map.Entry<K,V> floorEntry(K key) It will return the greatest key, less than or equal to the specified key, or null if there is no such key.
void forEach(BiConsumer<? super K,? super V> action) It will perform the given action for each entry in the map until all entries have been processed or the action throws an exception.
SortedMap<K,V> headMap(K toKey) It will return the key-value pairs whose keys are strictly less than toKey.
NavigableMap<K,V> headMap(K toKey, boolean inclusive) It will return the key-value pairs whose keys are less than (or equal to if inclusive is true) toKey.
Map.Entry<K,V> higherEntry(K key) It will return the least key strictly greater than the given key, or null if there is no such key.
K higherKey(K key) It will return true if this map contains a mapping for the specified key.
Set keySet() It will return the collection of keys that exist on the map.
Map.Entry<K,V> lastEntry() It will return the key-value pair having the greatest key, or null if there is no such key.
Map.Entry<K,V> lowerEntry(K key) It will return a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key.
K lowerKey(K key) It will return the greatest key strictly less than the given key, or null if there is no such key.
NavigableSet<K> navigableKeySet() It will return a NavigableSet view of the keys contained in this map.
Map.Entry<K,V> pollFirstEntry() It will eliminate and return a key-value mapping associated with the least key in this map, or null if the map is empty.
Map.Entry<K,V> pollLastEntry() It will eliminate and return a key-value mapping associated with the greatest key in this map, or null if the map is empty.
V put(K key, V value) It will add the specified value with the specified key in the map.
void putAll(Map<? extends K,? extends V> map) It will copy all the key-value pairs from one map to another map.
V replace(K key, V value) It will replace the specified value for a specified key.
boolean replace(K key, V oldValue, V newValue) It will replace the old value with the new value for a specified key.
void replaceAll(BiFunction<? super K,? super V,? extends V> function) It will replace each entry’s value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception.
NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) It will return key-value pairs whose keys range from fromKey to toKey.
SortedMap<K,V> subMap(K fromKey, K toKey) It will return key-value pairs whose keys range from fromKey, inclusive, to toKey, exclusive.
SortedMap<K,V> tailMap(K fromKey) It will return key-value pairs whose keys are greater than or equal to fromKey.
NavigableMap<K,V> tailMap(K fromKey, boolean inclusive) It will return key-value pairs whose keys are greater than (or equal to, if inclusive is true) fromKey.
boolean containsKey(Object key) It will return true if the map contains a mapping for the specified key.
boolean containsValue(Object value) It will return true if the map maps one or more keys to the specified value.
K firstKey() It will return the first (lowest) key currently in this sorted map.
V get(Object key) It will return the value to which the map maps the specified key.
K lastKey() It will return the last (highest) key currently in the sorted map.
V remove(Object key) It will eliminate or delete the key-value pair of the specified key from the map.
Set<Map.Entry<K,V>> entrySet() It will return a set view of the mappings contained in the map.
int size() It will return the number of key-value pairs that exist in the hashtable.
Collection values() It will return a collection view of the values contained in the map.

TreeMap example:

TreeMapTest.java

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
 
/**
 * This class is used to show the TreeMap functionality.
 * @author w3schools
 */
public class TreeMapTest {
	public static void main(String args[]){
		//Create TreeMap object.
		Map treeMap = new TreeMap();
 
		//Add objects to the TreeMap.
		treeMap.put(4, "Roxy");
		treeMap.put(2, "Sunil");
		treeMap.put(5, "Sandy");
		treeMap.put(1, "Munish");
		treeMap.put(3, "Pardeep");
 
		//Print the TreeMap object.
		System.out.println("TreeMap elements:");
		System.out.println(treeMap);
 
		//Get iterator
		Set set=treeMap.entrySet();  
		Iterator iterator=set.iterator();  
 
		//Print the TreeMap elements using iterator.
		System.out.println("TreeMap elements using iterator:");
		while(iterator.hasNext()){
		   Map.Entry mapEntry=(Map.Entry)iterator.next();  
		   System.out.println("Key: " + mapEntry.getKey() + ", " +
		   		"Value: " + mapEntry.getValue());  
		}  
	}
}

Output:

TreeMap elements:
{1=Munish, 2=Sunil, 3=Pardeep, 4=Roxy, 5=Sandy}
TreeMap elements using iterator:
Key: 1, Value: Munish
Key: 2, Value: Sunil
Key: 3, Value: Pardeep
Key: 4, Value: Roxy
Key: 5, Value: Sandy

 

TreeMap Example: remove():

import java.util.*;  
public class TreeMapExample{  
   public static void main(String args[]) {  
    TreeMap&lt;Integer,String&gt; map=new TreeMap&lt;Integer,String&gt;();    
      map.put(200,"A");    
      map.put(202,"B");    
      map.put(201,"C");    
      map.put(203,"D");    
      System.out.println("Before invoking the remove() method");  
      for(Map.Entry m:map.entrySet())  
      {  
          System.out.println(m.getKey()+" "+m.getValue());      
      }  
      map.remove(202);      
      System.out.println("After invoking the remove() method");  
      for(Map.Entry m:map.entrySet())  
      {  
          System.out.println(m.getKey()+" "+m.getValue());      
      }  
      }  
}

Output:

NavigableMap Example:

import java.util.*;  
public class TreeMapExample{  
 public static void main(String args[]){  
   NavigableMap&lt;Integer,String&gt; map=new TreeMap&lt;Integer,String&gt;();    
      map.put(200,"A");    
      map.put(202,"B");    
      map.put(201,"C");    
      map.put(203,"D");    
      //Maintains descending order  
      System.out.println("descendingMap: "+map.descendingMap());  
      //Returns key-value pairs whose keys are less than or equal to the specified key.  
      System.out.println("headMap: "+map.headMap(202,true));  
      //Returns key-value pairs whose keys are greater than or equal to the specified key.  
      System.out.println("tailMap: "+map.tailMap(202,true));  
      //Returns key-value pairs exist in between the specified key.  
      System.out.println("subMap: "+map.subMap(200, false, 202, true));   
 }  
}

Output:

SortedMap Example:

import java.util.*;  
public class TreeMapExample{  
 public static void main(String args[]){  
   SortedMap&lt;Integer,String&gt; map=new TreeMap&lt;Integer,String&gt;();    
      map.put(200,"A");    
      map.put(202,"B");    
      map.put(201,"C");    
      map.put(203,"D");    
      //Returns key-value pairs whose keys are less than the specified key.  
      System.out.println("headMap: "+map.headMap(202));  
      //Returns key-value pairs whose keys are greater than or equal to the specified key.  
      System.out.println("tailMap: "+map.tailMap(202));  
      //Returns key-value pairs exist in between the specified key.  
      System.out.println("subMap: "+map.subMap(200, 202));    
 }  
}

Output:

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