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CONVERT NULL VALUE TO A DEFAULT VALUE IN JAVA
Last updated: January 22, 2024
Written by: Eugene Kovko
* Core Java
* Java Null
Course – LS – All
GET STARTED WITH SPRING AND SPRING BOOT, THROUGH THE LEARN SPRING COURSE:
>> CHECK OUT THE COURSE
1. OVERVIEW
In 1965, Tony Hoare introduced the concept of a null reference. Since then,
countless hours have been spent reading the logs and trying to find the source
of NullPointerExceptions. This exception is so ubiquitous that it’s common to
refer to it as NPE.
In this tutorial, we’ll learn how to mitigate this problem. We’ll review several
techniques that simplify converting nulls to default values.
2. SIMPLE IF STATEMENTS
The easiest way to approach the conversion is to use if statements. They’re
basic language structures and benefit from being clear to developers with
different experiences and levels. The best part of this approach is that it’s
verbose, which simultaneously is the worst part:
@ParameterizedTest
@ArgumentsSource(ObjectsProvider.class)
void givenIfWhenNotNullThenReturnsDefault(String givenValue, String defaultValue) {
String actual = defaultValue;
if (givenValue != null) {
actual = givenValue;
}
assertDefaultConversion(givenValue, defaultValue, actual);
}Copy
Because we have total control over the logic, we can easily change, extract, and
reuse it. Additionally, we can make it lazy if we want:
@ParameterizedTest
@ArgumentsSource(ObjectsSupplierProvider.class)
void givenIfWhenNotNullThenReturnsDefault(String givenValue, String expected, Supplier<String> expensiveSupplier) {
String actual;
if (givenValue != null) {
actual = givenValue;
} else {
actual = expensiveSupplier.get();
}
assertDefaultConversion(givenValue, expected, actual);
}Copy
If the operations are quite simple, we can use a ternary operator to make them
more inlined. The Elvis operator didn’t make it into Java, but we still can
improve the code:
@ParameterizedTest
@ArgumentsSource(ObjectsProvider.class)
void givenTernaryWhenNotNullThenReturnsDefault(String givenValue, String defaultValue) {
String actual = givenValue != null ? givenValue : defaultValue;
assertDefaultConversion(givenValue, defaultValue, actual);
}Copy
Also, it allows a lazy approach as only the required expressions are evaluated:
@ParameterizedTest
@ArgumentsSource(ObjectsSupplierProvider.class)
void givenLazyTernaryWhenNotNullThenReturnsDefault(String givenValue, String expected,
Supplier<String> expensiveSupplier) {
String actual = givenValue != null ? givenValue : expensiveSupplier.get();
assertDefaultConversion(givenValue, expected, actual);
}Copy
We can extract this logic into a separate method with a good name to make our
code more readable. However, Java and some external libraries have done it
already.
3. JAVA OBJECTS
Java 9 provides us with two utility methods: Objects.requireNonNullElse and
Objects.requireNonNullElseGet. These methods have implementations similar to
those we reviewed. Overall, they provide a better API and make the code
self-explanatory:
@ParameterizedTest
@ArgumentsSource(ObjectsProvider.class)
void givenObjectsWhenNotNullThenReturnsDefault(String givenValue, String defaultValue) {
String actual = requireNonNullElse(givenValue, defaultValue);
assertDefaultConversion(givenValue, defaultValue, actual);
}Copy
Static imports can help us remove the Objects class name to reduce the noise.
The lazy version looks like this:
@ParameterizedTest
@ArgumentsSource(ObjectsSupplierProvider.class)
void givenLazyObjectsWhenNotNullThenReturnsDefault(String givenValue, String expected,
Supplier<String> expensiveSupplier) {
String actual = requireNonNullElseGet(givenValue, expensiveSupplier);
assertDefaultConversion(givenValue, expected, actual);
}Copy
However, this API is accessible starting only from Java 9. At the same time,
Java 8 also provides some convenient tools to achieve a similar result.
4. JAVA OPTIONAL<T>
The main idea behind the Optional<T> class was to fight the issue with null
checks and NullPointerExceptions. It’s possible to identify nullable APIs in
documentation, but a better solution is to show it explicitly in the code.
Getting an Optional<T> from some method unambiguously tells us the value might
be null. Also, IDEs can use static analysis for notifications and highlighting.
Explicit null checks weren’t the goal of this class. However, we can use it to
wrap a value we would like to check and do some operations over it:
@ParameterizedTest
@ArgumentsSource(ObjectsProvider.class)
void givenOptionalWhenNotNullThenReturnsDefault(String givenValue, String defaultValue) {
String actual = Optional.ofNullable(givenValue).orElse(defaultValue);
assertDefaultConversion(givenValue, defaultValue, actual);
}Copy
The lazy version looks quite similar:
@ParameterizedTest
@ArgumentsSource(ObjectsSupplierProvider.class)
void givenLazyOptionalWhenNotNullThenReturnsDefault(String givenValue, String expected,
Supplier<String> expensiveSupplier) {
String actual = Optional.ofNullable(givenValue).orElseGet(expensiveSupplier);
assertDefaultConversion(givenValue, expected, actual);
}Copy
Creating a separate wrapper object for a null check might be questionable. At
the same time, it might be useful for reaching through data objects without
chained null checks:
@Override
public Delivery calculateDeliveryForPerson(Long id) {
Person person = getPersonById(id);
if (person != null && person.getAddress() != null && person.getAddress().getZipCode() != null) {
ZipCode zipCode = person.getAddress().getZipCode();
String code = zipCode.getCode();
return calculateDeliveryForZipCode(code);
}
return Delivery.defaultDelivery();
}Copy
We can do the same, but using Optional.map(Function<T, U>):
public Delivery calculateDeliveryForPerson(Long id) {
return Optional.ofNullable(getPersonById(id))
.map(Person::getAddress)
.map(Address::getZipCode)
.map(ZipCode::getCode)
.map(this::calculateDeliveryForZipCode)
.orElse(Delivery.defaultDelivery());
}Copy
Wrapping objects in Optional<T> early on can reduce the checking we must do
later.
5. GUAVA LIBRARY
We can import Guava to get a similar functionality if all the previous methods
aren’t suitable, for example, when using earlier versions of Java. Let’s start
by adding the dependency:
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>33.0.0-jre</version>
</dependency>Copy
It mirrors the Java functionality and doesn’t add any explicitly useful
features. To get a default value if the provided is null, we can use
MoreObjects:
@ParameterizedTest
@ArgumentsSource(ObjectsProvider.class)
void givenGuavaWhenNotNullThenReturnsDefault(String givenValue, String defaultValue) {
String actual = MoreObjects.firstNonNull(givenValue, defaultValue);
assertDefaultConversion(givenValue, defaultValue, actual);
}Copy
MoreObjects replaces the Guava’s Objects utility class, which was deprecated and
planned for removal. However, it doesn’t allow the default value to be supplied
lazily. Also, it provides an Optional<T> class with the same name as Java but
resides in a different package:
@ParameterizedTest
@ArgumentsSource(ObjectsProvider.class)
void givenGuavaOptionalWhenNotNullThenReturnsDefault(String givenValue, String defaultValue) {
String actual = com.google.common.base.Optional.fromNullable(givenValue).or(defaultValue);
assertDefaultConversion(givenValue, defaultValue, actual);
}Copy
We can also implement a chain of modifications using this class as well:
@Override
public Delivery calculateDeliveryForPerson(Long id) {
return Optional.fromNullable(getPersonById(id))
.transform(Person::getAddress)
.transform(Address::getZipCode)
.transform(ZipCode::getCode)
.transform(this::calculateDeliveryForZipCode)
.or(Delivery.defaultDelivery());
}
Copy
The transform method doesn’t allow null-returning functions. Thus, we must
ensure that none of the methods in the pipeline returns null. Overall, Guava is
a good substitution for Java features if they’re unavailable, but it provides
less functionality than Java Optional<T>.
6. APACHE COMMONS
Another library we can use to simplify our null checks is Apache Commons. Let’s
add dependency:
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.14.0</version>
</dependency>Copy
However, it provides only simple methods to get the first non-null value out of
several arguments:
@ParameterizedTest
@ArgumentsSource(ObjectsProvider.class)
void givenApacheWhenNotNullThenReturnsDefault(String givenValue, String defaultValue) {
String actual = ObjectUtils.firstNonNull(givenValue, defaultValue);
assertDefaultConversion(givenValue, defaultValue, actual);
}Copy
The lazy version is a little bit inconvenient API, as it requires Supplier<T>,
so we’ll have to wrap a value if we already have one:
@ParameterizedTest
@ArgumentsSource(ObjectsSupplierProvider.class)
void givenLazyApacheWhenNotNullThenReturnsDefault(String givenValue, String expected,
Supplier<String> expensiveSupplier) {
String actual = ObjectUtils.getFirstNonNull(() -> givenValue, expensiveSupplier);
assertDefaultConversion(givenValue, expected, actual);
}Copy
Overall, this is also a nice substitution for Java features if they’re not
accessible to us for any reason.
7. CONCLUSION
NullPointerException is the most common exception developers face. There are
several convenient ways to ensure null safety. Java APIs and external libraries
provide many techniques. However, there’s nothing shameful to fall back to
simple if statements, as it’s clean, simple, and explicit.
The main goal of null checking is to do it as early as possible and ensure it’s
uniform across the project. The way we’re doing it isn’t essential.
As usual, all the code from the tutorial is available over on GitHub.
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