Java HashMap compute()

The syntax of the compute() method is:

hashmap.compute(K key, BiFunction remappingFunction)

Here, hashmap is an object of the HashMap class.

compute() Parameters

The compute() method takes 2 parameters:

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

Note: The remappingFunction can take two arguments. Hence, considered as BiFunction.

compute() Return Value

• returns the new value associated with the key
• returns null if no value associated with key

Note: If remappingFunction results null, then the mapping for the specified key is removed.

Example: HashMap compute() to Insert New Value

Output

HashMap: {Pant=150, Bag=300, Shoes=200}
Discounted Price of Shoes: 180
Updated HashMap: {Pant=150, Bag=300, Shoes=180

In the above example, we have created a hashmap named prices. Notice the expression,

prices.compute("Shoes", (key, value) -> value - value * 10/100)

Here,

• (key, value) -> value - value * 10/100 - It is a lambda expression. It reduces the old value of Shoes by 10% and returns it. To learn more about the lambda expression, visit Java Lambda Expressions.
• prices.compute() - Associates the new value returned by lambda expression to the mapping for Shoes.

We have used lambda expression as remapping function that rakes two parameters.

Note: According to the official documentation of Java, the HashMap merge() method is simpler than the compute() method.

Recommended Reading

• HashMap computeIfAbsent() - computes the value if the specified key is not mapped to any value
• HashMap computeIfPresent() - computes the value if the specified key is already mapped to a value