ConcurrentHashMap get() Method in Java

Last Updated : 14 Sep, 2018

The get() method of java.util.concurrent.ConcurrentHashMap is an in-built function in Java which accepts a key as parameter and returns the value mapped to it. It returns null if no mapping exists for the key passed as parameter.

Syntax:

Concurrent.get(Object key_element)

Parameters: The method accepts a single parameter key_element of object type which refers to the key whose associated value is supposed to be returned.

Return Value: The method returns the value associated with the key_element in the parameter.

Exception: The function throws NullPointerException when the specified key_element is null.

Below programs illustrate the use of java.util.concurrent.ConcurrentHashMap.get() method :

Program 1: This program involves mapping String Values to Integer Keys.

// Java Program Demonstrate get() 
// method of ConcurrentHashMap 
  
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"); 
        chm.put(103, "Contribute"); 
  
        // Displaying the HashMap 
        System.out.println("The Mappings are: "); 
        System.out.println(chm); 
  
        // Display the value of 100 
        System.out.println("The Value associated to "
                           + "100 is : " + chm.get(100)); 
  
        // Getting the value of 103 
        System.out.println("The Value associated to "
                           + "103 is : " + chm.get(103)); 
    } 
} 

Output:

The Mappings are: 
{100=Geeks, 101=for, 102=Geeks, 103=Contribute}
The Value associated to 100 is : Geeks
The Value associated to 103 is : Contribute

Program 2: This program involves mapping Integer Values to String Keys.

// Java Program Demonstrate get() 
// method of ConcurrentHashMap 
  
import java.util.concurrent.*; 
  
class GFG { 
    public static void main(String[] args) 
    { 
  
        ConcurrentHashMap<String, Integer> 
            chm = new ConcurrentHashMap<String, Integer>(); 
  
        chm.put("Geeks", 100); 
        chm.put("GFG", 10); 
        chm.put("GeeksforGeeks", 25); 
        chm.put("Contribute", 102); 
  
        // Displaying the HashMap 
        System.out.println("The Mappings are: "); 
        System.out.println(chm); 
  
        // Display the value of Geeks 
        System.out.println("The Value associated to "
                           + "Geeks is : " + chm.get("Geeks")); 
  
        // Getting the value of Contribute 
        System.out.println("The Value associated to "
                           + "Contribute is : " + chm.get("Contribute")); 
    } 
} 

Output:

The Mappings are: 
{GeeksforGeeks=25, Geeks=100, GFG=10, Contribute=102}
The Value associated to Geeks is : 100
The Value associated to Contribute is : 102

Reference : https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentHashMap.html#get()

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