August 7, 2019 - public <U> Optional<U> flatMap(Function<? super T, ?

May 28, 2019 - Using flatMap() with optionals is similar to using map(), with one important difference: if your transformation closure returns an optional, flatMap() will combine that optional with the existing optional, whereas map() will keep them both. Here’s a practical example so you can see the difference:

November 10, 2025 - Let’s see another example to get a better understanding of this situation: assertEquals(Optional.of(Optional.of("STRING")), Optional .of("string") .map(s -> Optional.of("STRING"))); As we can see, we end up with the nested structure ...

August 10, 2022 - class Test { public static void main(String[] args) { Student student = new Student("John", "Smith", 8); student.setAddress(Optional.of("5th Avenue, New York")); Optional<Student> studentOptional = Optional.ofNullable(student); studentOptional .filter(s1 -> s1.getGrade() > 7) // returns Optional<Student[fName, lName, grade, Optional<String> address]> .flatMap(s1 -> s1.getAddress()) // returns Optional<String> .ifPresent(item -> System.out.println(item)); } }

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December 8, 2023 - Here’s a simplified representation of the flatMap() method: Optional<T> optional = ...

In this example, the map function takes a closure that multiplies the optional integer by 2 (if it is not nil). The flatMap function can be used to flatten a nested optional.

October 4, 2024 - Optional<String> optionalString = Optional.of("Hello"); Optional<Integer> stringLength = optionalString.map(String::length); In this example, the optionalString contains the value "Hello", so the map() the operation will calculate its length ...

October 23, 2024 - By using flatMap(), you can unwrap the Optional, process the stream or collection it holds, and continue working with a flat stream of data. For example, let’s say you have an Optional<List<String>>, where the list might be empty or non-existent.

August 12, 2025 - package com.core.java.functional; import java.util.Optional; public class Citizen { class Continent { public Continent(String name) { this.name = name; } public String name; public Country country; } class Country { public Country(String name) { this.name = name; } public String name; public State state; } class State { public State(String name) { this.name = name; } public String name; public City city; } class City { public City(String name) { this.name = name; } public String name; public Suburb suburb; } class Suburb { public Suburb(String name) { this.name = name; } public String name; pu

Evaluates the given closure when this instance is not , passing the unwrapped value as a parameter.

December 9, 2023 - flatMap() correctly flattens this to a single Optional<String>.

November 9, 2024 - Let’s revisit the User example, but this time assume we want the city name in uppercase. We can apply both transformations seamlessly with map(): Optional<String> upperCaseCity = user .flatMap(User::getProfile) .flatMap(Profile::getAddress) .map(Address::getCity) .map(String::toUpperCase); upperCaseCity.ifPresent(System.out::println); // Prints the city in uppercase if present

January 5, 2021 - As you all know, the Optional object ... Optional<Optional<String>>. To resolve this problem, Java introduces us to the flatMap() method so that Optional’s data type is simpler: Optional<String> for example....

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

January 8, 2018 - Function<String, Optional<Long>> toLongOpt = Long::parseLongOpt; Optional<String> someString = Optional.of("12L"); Optional<Long> someLong = someString.flatMap(toLongOpt); For Stream, we can use it in a situation where the function we want to ...

Options to flatMap a list of Optionals in Java8 · Raw · flatmap_optionals.java · This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.

January 23, 2022 - The blog post How I learnt to like Optional shows an example of how to chain Optional values safely, using Optional.orElse() to provide empty objects for the next level in the chain. This blog post uses Optional.flatMap() and Optional.map(), to achieve the same thing, without having to create the empty objects, and without doing any…

January 8, 2024 - List<String> filteredList = listOfOptionals.stream() .flatMap(o -> o.map(Stream::of).orElseGet(Stream::empty)) .collect(Collectors.toList()); All this will get quite simplified with the arrival of Java 9 that adds a stream() method to Optional.