ConcurrentHashMap size() Method in Java
Last Updated :
20 Feb, 2023
The size() method in Java’s ConcurrentHashMap class is used to retrieve the number of key-value mappings in the map. It has the following signature:
int size()
The size() method works in a concurrent environment, which means that it can be called from multiple threads without causing any data race or synchronization issues.
When a size() operation is performed, the method first acquires the lock on all the segments of the map and then calculates the total number of key-value mappings in the map.
Here is an example of using the size() method:
Java
import java.util.concurrent.ConcurrentHashMap;
public class ConcurrentHashMapExample {
public static void main(String[] args) {
ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
map.put("Alice", 25);
map.put("Bob", 30);
map.put("Charlie", 35);
int size = map.size();
System.out.println("Size of the map: " + size);
}
}
|
Output
Size of the map: 3
In this example, we first create a ConcurrentHashMap and add three key-value pairs to it using the put() method.
Next, we perform a size() operation to retrieve the number of key-value mappings in the map. The method returns 3, and we print out the result.
The java.util.concurrent.ConcurrentHashMap.size() method is an in-built function in Java that counts the number of key-value mappings in this map and returns the integer value.
Syntax:
public int size()
Return Value: The function returns an integer value that denotes the number of key-value mappings in this map. Below program illustrates the use of the size() method:
Program 1:
Java
import java.util.concurrent.*;
class GFG {
public static void main(String[] args)
{
ConcurrentHashMap<Integer, String> chm
= new ConcurrentHashMap<Integer, String>();
chm.put(100, "Geeks");
chm.put(101, "for");
chm.put(102, "Geeks");
System.out.println("The number of "
+ "key-value mappings is "
+ chm.size());
}
}
|
The number of key-value mappings is 3
Program 2:
Java
import java.util.concurrent.*;
class GFG {
public static void main(String[] args)
{
ConcurrentHashMap<Integer, Integer> chm
= new ConcurrentHashMap<Integer, Integer>();
chm.put(1, 100);
chm.put(2, 200);
chm.put(3, 300);
chm.put(4, 400);
chm.put(5, 500);
chm.put(6, 600);
System.out.println("The number of "
+ "key-value mappings is "
+ chm.size());
}
}
|
The number of key-value mappings is 6
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