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Java HashMap computeifPresent()
Java HashMap
Java HashMap computeIfPresent() is a method in the Java HashMap class that updates the value of a key in the HashMap if the key is present in the HashMap.
The method takes two parameters, a key and a BiFunction object that takes the key and the current value of the key as input and returns a new value for the key.
- To understand the Java HashMap Compute() Method, Read the Complete Article.
The computeifPresent() method performs the following operations:
- Here are the methods to perfrom following operations.
- Checks if the specified key is present in the map. If the key is not present, the computeIfPresent() method does nothing and returns null.
- If the key is present, the computeIfPresent() method retrieves the current value associated with the key.
- The computeIfPresent() method applies the specified function (passed as the second argument) to the key and current value. The function must return the new value for the key.
- The computeIfPresent() method then associates the new value with the key in the map and returns the new value.
- If the function passed to computeIfPresent() returns null, the key is removed from the map.
public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)
V computeIfPresent(K key, BiFunction remappingFunction)
where K is the type of the key, V is the type of the value, and remappingFunction is the function used to compute the new value.
Let’s look at the Java HashMap computeifpresent() Method to perform certain operations.
Example 1: Java Program to run use computeifpresent Method.
import java.util.HashMap; public class Main { public static void main(String[] args) { // Create a HashMap with some initial mappings HashMap<String, Integer> map = new HashMap<>(); map.put("ayush", 1); map.put("ashish", 2); // Insert a new value using the compute() method map.compute("anjali", (key, value) -> value == null ? 3 : value); // Print the updated HashMap System.out.println(map); } }
Output
{banana=2, apple=2}
Example 2 :Java Program to use Computeifpresent() Method
import java.util.HashMap; import java.util.Map; public class Main { public static void main (String[]args) { // Create a new HashMap Map < String, Integer > map = new HashMap <> (); // Add some key-value pairs map.put ("apple", 1); map.put ("banana", 2); map.put ("cherry", 3); // Compute a new value for an existing key map.computeIfPresent ("banana", (key, value)->value * 2); // Print the updated map System.out.println (map); } }
Output
{banana=4, apple=1, cherry=3}
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