Java ConcurrentHashMap mappingCount() Method

The mappingCount() method of ConcurrentHashMap class returns the number of mappings. The value returned is an estimated value; the actual count may differ if there are concurrent insertions or removals.

Syntax

Parameter

No parameter is passed.

Returns

the number of mappings

Throws

No exception is thrown.

Example 1

import java.util.concurrent.ConcurrentHashMap; 
import java.util.*; 
  
public class ConcurrentHashMapmappingCountExample1 { 
  
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<String, String> chm = new ConcurrentHashMap<String, String>(); 

        chm.put("1", "1"); 
        chm.put("2", "10"); 
        chm.put("3", "100"); 
        chm.put("4", "2"); 
        chm.put("5", "20"); 
        chm.put("6", "200"); 
         // print statement.
        System.out.println("size of map before clearing: " + chm.mappingCount()); 
        chm.clear(); // clear will clear all the values in map.
        System.out.println("Map after calling clear(): "+ chm); 
        System.out.println("size of map after clearing: " + chm.mappingCount()); 
    } 
}

Test it Now

Output:

size of map before clearing: 6
Map after calling clear(): {}
size of map after clearing: 0

Example 2

import java.util.*; 
import java.util.concurrent.*; 
  
public class ConcurrentHashMapmappingCountExample2  { 
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<Integer, String>  conmap = new ConcurrentHashMap<Integer, String>(); 
        conmap.put(10, "Java"); 
        conmap.put(11, ".net"); 
        conmap.put(20, "php"); 
        conmap.put(12, "C"); 
        conmap.put(30, "C++"); 
  
        System.out.println(" Map : " + conmap); 
       
         System.out.println("keySet : " + conmap.keySet());
         System.out.println("Map Size  : " + conmap.mappingCount());
    } 
}

Test it Now

Output:

Map : {20=php, 10=Java, 11=.net, 12=C, 30=C++}
keySet : [20, 10, 11, 12, 30]
Map Size  : 5

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