Java Utility Library

Java Hashtable - computeIfPresent() Method

The java.util.Hashtable.computeIfPresent() method is used to update a value in the Hashtable, if the specified key is present and non-null. It tries to compute a new mapping given the key and its current mapped value. If the function returns null, the mapping is removed. If the function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

Syntax

public V computeIfPresent(
    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

`key`	Specify the key with which the specified value is to be associated.
`remappingFunction`	Specify the function to compute a value.

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.Hashtable.computeIfPresent() method is used to update a value in the given Hashtable.

import java.util.*;

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

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

    //printing the Hashtable
    System.out.println("Htable contains: " + Htable);    

    //updating value of the specified key using computeIfPresent method
    Htable.computeIfPresent(103, (k, v) -> "Sam"); 
    Htable.computeIfPresent(104, (k, v) -> "Lee"); 

    //printing the Hashtable
    System.out.println("Htable contains: " + Htable);  
  }
}

The output of the above code will be:

Htable contains: {104=Jo, 103=Kim, 102=Marry, 101=John}
Htable contains: {104=Lee, 103=Sam, 102=Marry, 101=John}

❮ Java.util - Hashtable