TreeMap in Java

Introduction

The TreeMap in Java is used to implement Map interface and NavigableMap along with the AbstractMap Class. The map is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used. This proves to be an efficient way of sorting and storing the key-value pairs. The storing order maintained by the treemap must be consistent with equals just like any other sorted map, irrespective of the explicit comparators. The treemap implementation is not synchronized in the sense that if a map is accessed by multiple threads, concurrently and at least one of the threads modifies the map structurally, it must be synchronized externally.

Constructor

1. TreeMap()

   // Java Program to Demonstrate TreeMap
   // using the Default Constructor
   // Importing required classes
   import java.util.*;
   import java.util.concurrent.*;
   // Main class
   // TreeMapImplementation
   public class GFG {
   // Method 1
   // To show TreeMap constructor
   static void Example1stConstructor()
   {
       // Creating an empty TreeMap
       TreeMap<Integer, String> tree_map
           = new TreeMap<Integer, String>();
   
       // Mapping string values to int keys
       // using put() method
       tree_map.put(10, "Geeks");
       tree_map.put(15, "4");
       tree_map.put(20, "Geeks");
       tree_map.put(25, "Welcomes");
       tree_map.put(30, "You");
   
       // Printing the elements of TreeMap
       System.out.println("TreeMap: " + tree_map);
   }
   
   // Method 2
   // Main driver method
   public static void main(String[] args)
   {
       System.out.println("TreeMap using "
                          + "TreeMap() constructor:\n");
   
       // Calling constructor
       Example1stConstructor();
   }
   }

2. TreeMap(Comparator comp)

   // Java program to Illustrate Updation of Elements
   // in TreeMap using put() Method
   // Importing required classes
   import java.util.*;
   // Main class
   class GFG {
   // Main driver method
   public static void main(String args[])
   {
       // Initialization of a TreeMap
       // using Generics
       TreeMap<Integer, String> tm
           = new TreeMap<Integer, String>();
       // Inserting the elements in Map
       // using put() method
       tm.put(3, "Geeks");
       tm.put(2, "Geeks");
       tm.put(1, "Geeks");
       // Print all current elements in map
       System.out.println(tm);
       // Inserting the element at specified
       // corresponding to specified key
       tm.put(2, "For");
       // Printing the updated elements of Map
       System.out.println(tm);
   }
   }

3. TreeMap(Map M)

   // Java program to Illustrate Removal of Elements
   // in TreeMap using remove() Method
   // Importing required classes
   import java.util.*;
   // Main class
   class GFG {
   // Main driver method
   public static void main(String args[])
   {
       // Initialization of a TreeMap
       // using Generics
       TreeMap<Integer, String> tm
           = new TreeMap<Integer, String>();
       // Inserting the elements
       // using put() method
       tm.put(3, "Geeks");
       tm.put(2, "Geeks");
       tm.put(1, "Geeks");
       tm.put(4, "For");
       // Printing all elements of Map
       System.out.println(tm);
       // Removing the element corresponding to key
       tm.remove(4);
       //  Printing updated TreeMap
       System.out.println(tm);
   }
   }

4. TreeMap(SortedMap sm)

   // Java Program to Illustrate Iterating over TreeMap
   // using
   // Importing requried classes
   import java.util.*;
   // Main class
   class GFG {
   // Main driver method
   public static void main(String args[])
   {
       // Initialization of a TreeMap
       // using Generics
       TreeMap<Integer, String> tm
           = new TreeMap<Integer, String>();
       // Inserting the elements
       // using put() method
       tm.put(3, "Geeks");
       tm.put(2, "For");
       tm.put(1, "Geeks");
       // For-each loop for traversal over Map
       // via entrySet() Method
       for (Map.Entry mapElement : tm.entrySet()) {
           int key = (int)mapElement.getKey();
           // Finding the value
           String value = (String)mapElement.getValue();
           // Printing the key and value
           System.out.println(key + " : " + value);
       }
   }
   }