Master Java’s HashMap: Unlocking the Power of ComputeIfPresent

Unlock the Power of Java’s HashMap: ComputeIfPresent Method

When working with Java’s HashMap, it’s essential to understand the various methods that allow you to manipulate and update its contents efficiently. One such method is computeIfPresent(), which enables you to recompute the value associated with a specific key.

Understanding the Syntax

The computeIfPresent() method takes two parameters:

• key: the key with which the computed value is to be associated
• remappingFunction: a function that computes the new value for the specified key

This remappingFunction can take two arguments, making it a BiFunction.

Return Value

The computeIfPresent() method returns:

• The new value associated with the specified key
• null if no value is associated with the key

A Key Insight

If the remappingFunction results in null, the mapping for the specified key is removed.

Putting it into Practice

Let’s consider an example where we have a HashMap named prices. We want to update the value associated with the key “Shoes” by adding a 10% increase.

java
prices.computeIfPresent("Shoes", (key, value) -> value + value*10/100);


In this example, the lambda expression (key, value) -> value + value*10/100 acts as the remapping function, taking two parameters. It computes the new value of “Shoes” and returns it. This new value is then associated with the key “Shoes” in the HashMap.

Important Note

Keep in mind that you cannot use the computeIfPresent() method if the key is not present in the HashMap.

Exploring Related Methods

To further enhance your understanding of Java’s HashMap, be sure to check out:

• compute(): computes a new value for a key
• computeIfAbsent(): computes a new value if the key is not present
• merge(): merges a new value with an existing value