The HashMap.compute() method in Java computes a new value for the specified key.
hashmap.compute(K key, BiFunction remappingFunction)
key: The key for which the new value is to be computed.
remappingFunction: A BiFunction that takes two arguments as input and returns a single value. The value returned from the BiFunction will be used to update the passed key of the map. If we return null from the BiFunction, then the mapping for the key will be removed.
The compute method will return the new value associated with the key.
import java.util.HashMap;class merge {public static void main( String args[] ) {HashMap<String, Integer> map = new HashMap<>();map.put("Maths", 50);map.put("Science", 60);map.put("Programming", 70);System.out.println( "The map is - " + map);System.out.println( "\n---------------\n");System.out.println( "Calling compute function for key Maths");Integer newVal = map.compute("Maths", (key, oldVal) -> { return oldVal + 10; });System.out.println("\nThe return value is " + newVal);System.out.println( "The map is - " + map);System.out.println( "\n---------------\n");System.out.println( "Calling compute function for key Economics\n");newVal =map.compute("Economics",(key, oldVal) -> {System.out.print("Inside BiFunction: The key is ");System.out.print(key);System.out.print(". The value is ");System.out.println(oldVal + ".");if(oldVal != null) {return oldVal + 10;}return null;});System.out.println("\nThe return value is " + newVal);System.out.println( "The map is - " + map);}}
In the code above, we created a HashMap with the name map and added some entries to it.
First, we called the compute method on the map for the Maths key.
Integer newVal = map.compute("Maths", (key, oldVal) -> { return oldVal + 10; });
The code above will compute a new value inside the BiFunction and update the value associated with the Maths key.
Then, we called the compute method on the map for the Economics key. There is no mapping associated with the Economics key, so the map remains unchanged. We added the null check inside the BiFunction passed to the compute method because the BiFunction will be called with the argument:
key as Economics.oldVal as null.To handle the null of the oldVal, we added the null check.