Java HashMap - compute() Method

The java.util.HashMap.compute() method is used to update a value in the HashMap. It tries to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping). If the function returns null, the mapping is removed (or remains absent if initially absent). If the function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

Syntax

public V compute(K key, 
                 BiFunction<? super K,? super V,? extends V> remappingFunction)

Here, K and V are the type of key and value respectively maintained by the container.

Parameters

Return Value

Returns the new value associated with the specified key, or null if none.

Exception

NA.

Example:

In the example below, the java.util.HashMap.compute() method is used to update a value in the given HashMap.

import java.util.*;

public class MyClass {
  public static void main(String[] args) {
    //creating a HashMap
    HashMap<Integer, String> MyMap = new HashMap<Integer, String>();

    //populating the HashMap
    MyMap.put(101, "John");
    MyMap.put(102, "Marry");
    MyMap.put(103, "Kim");
    MyMap.put(104, "Jo");

    //printing the HashMap
    System.out.println("MyMap contains: " + MyMap);    

    //updating value of the specified key using compute method
    MyMap.compute(101, (k, v) -> v.concat(" Paul")); 
    MyMap.compute(104, (k, v) -> "Sam"); 

    //printing the HashMap
    System.out.println("MyMap contains: " + MyMap);  
  }
}

The output of the above code will be:

MyMap contains: {101=John, 102=Marry, 103=Kim, 104=Jo}
MyMap contains: {101=John Paul, 102=Marry, 103=Kim, 104=Sam}