This code example shows how to get the size or number of keys and values stored in TreeMap using the size().

To get the size, use the size() of the TreeMap class that returns the number of key/value pairs stored in a TreeMap of objects.

The results obtained are displayed before and after adding and removing elements.

import java.util.*; 

public class TreeMap_size {
 public static void main(String[] args) {
 // creating TreeMap
 TreeMap< Integer, String> treemap = new TreeMap< Integer, String> (); 
 
 // insert into treemap
 treemap.put(1, "ab"); 
 treemap.put(2, "ba"); 
 treemap.put(3, "bc"); 
 
 //display elements
 Set set=treemap.keySet(); 
 Iterator iterator = set.iterator(); 
 while(iterator.hasNext()){
 Integer key = ((Integer) iterator.next()); 
 String val = ((String) treemap.get(key)); 
 System.out.println(key+"-> "+val); 
 }
 
 //initial treemap size
 System.out.println("before: "+treemap.size()+" element(s)"); 
 
 //add key/value
 treemap.put(4, "cb"); 
 System.out.println("after adding: "+treemap.size()+" element(s)"); 
 
 String val = treemap.remove(3); 
 System.out.println("after removing "+val+": "+treemap.size()+" element(s)"); 
 } 
}

Output:

1-> ab
2-> ba
3-> bc
before: 3 item(s)
after addition: 4 item(s)
after deletion of bc: 3 item(s)

References:
JavaDoc: TreeMap size() method