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HashMap computeIfPresent(key, BiFunction) method in Java with Examples
  • Last Updated : 15 Oct, 2019

The computeIfPresent(Key, BiFunction) method of HashMap class which allows you to compute value of a mapping for specified key if key is already associated with a value (or is mapped to null).

  • If mapping function of this method returns null, the mapping is removed.
  • If the remapping function throws an exception, the exception is rethrown, and the mapping is left unchanged.
  • During computation, modification this map using this method is not allowed.
  • Syntax:

    public Object computeIfPresent(Object key,
                      BiFunction remappingFunction)

    Parameters: This method accepts two parameters:

    • key: key with which the value is to be associated.
    • remappingFunction: function to do the operation on value.

    Returns: This method returns new remapped value associated with the specified key, or null if mapping returns null.

    Below programs illustrate the computeIfPresent(Key, BiFunction) method:



    Example 1: This example demonstrates the case when the key is not in the hashmap.




    // Java program to demonstrate
    // computeIfPresent(Key, BiFunction) method.
      
    import java.util.concurrent.*;
    import java.util.*;
      
    public class GFG {
        public static void main(String[] args)
        {
      
            // Create a HashMap and add some values
            HashMap<String, Integer> wordCount = new HashMap<>();
            wordCount.put("Geeks", 1);
            wordCount.put("for", 2);
            wordCount.put("geeks", 3);
      
            // print HashMap details
            System.out.println("Hashmap before operation :\n "
                               + wordCount);
      
            // provide new value for keys which is present
            // using computeIfPresent method
            wordCount.computeIfPresent("Geek",
                                       (key, val) -> val + 100);
      
            // print new mapping
            System.out.println("HashMap after operation :\n "
                               + wordCount);
        }
    }
    Output:
    Hashmap before operation :
     {geeks=3, Geeks=1, for=2}
    HashMap after operation :
     {geeks=3, Geeks=1, for=2}
    

    Example 2: This example demonstrates the case when the key is present in the hashmap.




    // Java program to demonstrate
    // computeIfPresent(Key, BiFunction) method.
      
    import java.util.concurrent.*;
    import java.util.*;
      
    public class GFG {
        public static void main(String[] args)
        {
      
            // Create a HashMap and add some values
            HashMap<String, Integer> wordCount = new HashMap<>();
            wordCount.put("Geeks", 1);
            wordCount.put("for", 2);
            wordCount.put("geeks", 3);
      
            // print HashMap details
            System.out.println("Hashmap before operation :\n "
                               + wordCount);
      
            // provide new value for keys which is present
            // using computeIfPresent method
            wordCount.computeIfPresent("for",
                                       (key, val) -> val + 1);
      
            // print new mapping
            System.out.println("HashMap after operation :\n "
                               + wordCount);
        }
    }
    Output:
    Hashmap before operation :
     {geeks=3, Geeks=1, for=2}
    HashMap after operation :
     {geeks=3, Geeks=1, for=3}
    

    Reference: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#computeIfPresent-K-java.util.function.BiFunction-

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