Java -TreeMap class

• TreeMap contains values based on the key. It implements the NavigableMap interface and extends AbstractMap class.
• TreeMap contains only unique elements.
• TreeMap cannot have null key but can have multiple null values.
• TreeMap is same as HashMap instead maintains ascending order.
• TreeMap is unsynchronized collection class which means it is not suitable for thread-safe operations until unless synchronized explicitly.

TreeMap Example

1. import java.util.*;
2. class TreeMapDemo
   {
3.  public static void main(String args[]){
5.   TreeMap<Integer,String> tm=new TreeMap<Integer,String>();
7.   tm.put(100,“A”);
8.   tm.put(102,“B”);
9.   tm.put(101,“C”);
10.   tm.put(103,“D”);
12.   for(Map.Entry hm:tm.entrySet()){
13.    System.out.println(hm.getKey()+” “+hm.getValue());
14.   }
15.  }
16. }

    Output:

           100 A
           101 C
           102 B
           103 D

Another TreeMap Example

import java.util.TreeMap;
import java.util.Set;
import java.util.Iterator;
import java.util.Map;

public class TreeMapDemo1

 {

   public static void main(String args[]) {

      /* This is how to declare TreeMap */
      TreeMap<Integer, String> tmp = 
             new TreeMap<Integer, String>();

      /*Adding elements to TreeMap*/
      tmp.put(1, "A");
      tmp.put(2, "B");
      tmp.put(5, "C");
      tmp.put(3, "D");
      tmp.put(4, "E");

      /* Display content using Iterator*/
      Set set = tmp.entrySet();
      Iterator iterator = set.iterator();
      while(iterator.hasNext()) {
         Map.Entry m = (Map.Entry)iterator.next();
         System.out.print("key is: "+ m.getKey() + " & Value is: ");
         System.out.println(m.getValue());
      }

   }
}

Output:

key is: 1 & Value is: A
key is: 2 & Value is: B
key is: 3 & Value is: D
key is: 4 & Value is: E
key is: 5 & Value is: C