Optional

Optional says explicitly: the result may be absent

A method sometimes cannot find a value. Returning null communicates this implicitly: the calling code has to remember the check on its own. Optional<T> makes the absence of a result part of the return type.

Optional<String> findName(int id) {
    if (id == 1) {
        return Optional.of("Alice");
    }
    return Optional.empty();
}

Optional.of(value) is used for a value that is guaranteed to be non-null, Optional.ofNullable(value) also accepts null, and Optional.empty() creates an empty result.

Work with the value through Optional operations

Instead of a manual “check — extract — transform” sequence, it is often more convenient to continue the computation through map, filter, and flatMap.

Optional<Integer> length = findName(1)
        .filter(name -> !name.isBlank())
        .map(String::length);

If the name exists and is not blank, the result is an Optional containing the length. If the value was absent or failed the filter, the result remains empty.

A default value or an exception

orElse returns a fallback value, orElseGet computes it through a Supplier only when needed, and orElseThrow reports the missing value with an exception.

String name = findName(10)
        .orElse("Unknown");

If creating the fallback value is expensive or has a side effect, orElseGet is usually the better choice: the argument of orElse is evaluated before the method call, even when the Optional already contains a value.

Do not turn Optional back into a hidden null

The get() method exists, but calling it directly without a guarantee that a value is present brings back the same problem: instead of a NullPointerException, you can now get a NoSuchElementException. Intent is usually expressed better with orElse, orElseThrow, ifPresent, or a chain of transformations.