java.util.Optional#map

The map method in the java.util.Optional class is a powerful tool for transforming the value contained within an Optional instance if it is present. It is commonly used for operations on potentially nullable values without the need for explicit null checks. Here's a detailed look at how Optional.map works:

Method Signature

public <U> Optional<U> map(Function<? super T, ? extends U> mapper)

Description

• Type Parameters:
  • <U> - The type of the value returned from the mapping function.
• Parameters:
  • mapper - A function to apply to the value, if present.
• Returns:
  • An Optional describing the result of applying a mapping function to the value of this Optional, if a value is present, otherwise an empty Optional.

Usage

• Input: An Optional containing a value (or empty).
• Process: Apply the provided mapping function to the contained value if present.
• Output: A new Optional containing the result of the mapping function, or an empty Optional if the original Optional was empty.

Example Usage

Basic Example

Optional<String> name = Optional.of("Alice");
Optional<Integer> nameLength = name.map(String::length);

System.out.println(nameLength); // Output: Optional[5]

In this example, map applies the String::length method to the value inside the Optional if it is present, transforming it from Optional<String> to Optional<Integer>.

Handling Empty Optionals

Optional<String> emptyName = Optional.empty();
Optional<Integer> emptyNameLength = emptyName.map(String::length);

System.out.println(emptyNameLength); // Output: Optional.empty

Practical Example

Consider a more practical scenario where you want to extract and transform a value from an Optional object inside a stream of data:

import java.util.List;
import java.util.Optional;

public class Main {
    public static void main(String[] args) {
        List<Optional<String>> names = List.of(Optional.of("Alice"), Optional.empty(), Optional.of("Bob"));
        
        names.stream()
            .map(opt -> opt.map(String::toUpperCase))
            .forEach(System.out::println);
    }
}