Master Java 8 Optional and Lambda: Reduce Null Checks and Write Cleaner Code

Many developers still use JDK8; this article introduces useful JDK8 features such as Optional and lambda expressions.

Optional class

Optional helps handle nulls elegantly, avoiding NullPointerException.

Java7 null‑check example:

User user = usersMapper.selectUserById(userId);
String userName = user.getUserName();
if (user != null) {
    if (userName != null && !userName.isEmpty()) {
        // ...
    }
}

Java8 Optional version:

User user = usersMapper.selectUserById(userId);
Optional.ofNullable(user)
        .map(User::getUserName)
        .ifPresent(userName -> {
            // ...
        });

Common Optional methods:

ofNullable – returns Optional of value or empty if null

empty – returns empty Optional

filter – returns Optional if value matches predicate

flatMap – applies function returning Optional

get – returns value or throws NoSuchElementException

ifPresent – executes consumer if value present

isPresent – true if value present

map – applies function and wraps result in Optional

of – wraps non‑null value, throws NPE if null

orElse – returns value or default

orElseGet – returns value or result of Supplier

orElseThrow – returns value or throws supplied exception

Difference between map and flatMap: map takes Function<? super T, ? extends U> and wraps the result in an Optional; flatMap takes Function<? super T, Optional<U>> and returns the Optional directly.

map:
public <U> Optional<U> map(Function<? super T, ? extends U> mapper) {
    Objects.requireNonNull(mapper);
    if (!isPresent())
        return empty();
    else
        return Optional.ofNullable(mapper.apply(value));
}

flatMap:
public <U> Optional<U> flatMap(Function<? super T, Optional<U>> mapper) {
    Objects.requireNonNull(mapper);
    if (!isPresent())
        return empty();
    else
        return Objects.requireNonNull(mapper.apply(value));
}

Lambda expressions

Lambda provides a concise way to pass behavior as parameters, replacing anonymous inner classes.

Java7 loop vs Java8 lambda:

Java7:
List<String> stringList = Arrays.asList("1","2","3");
for (String st : stringList) {
    System.out.println(st);
}

Java8:
Arrays.asList("1","2","3").forEach(st -> {
    System.out.println(st);
});

Adopting these features reduces boilerplate, improves readability, and boosts development efficiency.