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Java 8 Optional - Avoid Null and NullPointerException Altogether - and Keep It Pretty

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Java 8 Optional - Avoid Null and NullPointerException Altogether - and Keep It Pretty

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There have been a couple of articles on null, NPE's and how to avoid them. They make some point, but could stress the easy, safe, beautiful aspects of Java 8's Optional. This article shows some way of dealing with optional values, without additional utility code.

The old way

Let's consider this code:

String unsafeTypeDirName = project.getApplicationType().getTypeDirName();
System.out.println(unsafeTypeDirName);

This can obviously break with NullPointerException if any term is null.

A typical way of avoiding this:

// safe, ugly, omission-prone
if (project != null) {
    ApplicationType applicationType = project.getApplicationType();
    if (applicationType != null) {
        String typeDirName = applicationType.getTypeDirName();
        if (typeDirName != null) {
            System.out.println(typeDirName);
        }
    }
}

This won't explode, but is just ugly, and it's easy to avoid some null check.

Java 8

Let's try with Java 8's Optional:

// let's assume you will get this from your model in the future; in the meantime...
Optional<Project> optionalProject = Optional.ofNullable(project);

// safe, java 8, but still ugly and omission-prone
if (optionalProject.isPresent()) {
    ApplicationType applicationType = optionalProject.get().getApplicationType();
    Optional<ApplicationType> optionalApplicationType = Optional.ofNullable(applicationType);
    if (optionalApplicationType.isPresent()) {
        String typeDirName = optionalApplicationType.get().getTypeDirName();
        Optional<String> optionalTypeDirName = Optional.ofNullable(typeDirName);
        if (optionalTypeDirName.isPresent()) {
            System.out.println(optionalTypeDirName);
        }
}

As noted in a lot of posts, this isn't a lot better than null checks. Some argue that it makes your intent clear. I don't see any big difference, most null checks being pretty obvious on those kind of situations.

Ok, let's use the functional interfaces and get more power from Optional:

// safe, prettier
Optional<String> optionalTypeDirName = optionalProject
        .flatMap(project -> project.getApplicationTypeOptional())
        .flatMap(applicationType -> applicationType.getTypeDirNameOptional());
optionalTypeDirName.ifPresent(typeDirName -> System.out.println(typeDirName));

flatMap() will always return an Optional, so no nulls possible here, and you avoid having to wrap/unwrap to Optional.

Please note that I added *Optional() methods in the types for that. There are other ways to do it (map + flatMap to Optional::ofNullable is one). The best one: only return optional value where it makes sense: if you know the value will always be provided, make it non-optional. By the way, this advice works for old style null checks too.

ifPresent() will only run the code if it's there. No default or anything.

Let's just use member references to express the same in a tight way:

// safe, yet prettier
optionalProject
        .flatMap(Project::getApplicationTypeOptional)
        .flatMap(ApplicationType::getTypeDirNameOptional)
        .ifPresent(System.out::println);

Or if you know that  Project has an ApplicationType anyway:

// safe, yet prettier
optionalProject
        .map(Project::getApplicationType)
        .flatMap(ApplicationType::getTypeDirNameOptional)
        .ifPresent(System.out::println);


Conclusion

By using Optional, and never working with null, you could avoid null checks altogether. Since they aren't needed, you also avoid omitting a null check leading to NPEs. Still, make sure that values returned from legacy code (Map, ...), which can be null, are wrapped asap in Optional.

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Topics:
java ,high-perf ,performance ,tips and tricks ,optional ,java 8 ,null ,npe ,nullpointerexception

Opinions expressed by DZone contributors are their own.

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