How to avoid NullPointerException in Java using Optional?
Optional was introduced in Java 8 as a way to handle potentially null values more safely and expressively. It helps to avoid NullPointerException and makes the code more readable.
Hands on
Creating an Optional
Optional can be created in several ways:
Optional<String> name = Optional.of("Bob");
Optional<String> nameNullable = Optional.ofNullable("Mary");
Optional<String> nameNullable2 = Optional.ofNullable(null);
Optional<String> nameEmpty = Optional.empty();- Optional.of(): Does not accept null values and returns an Optional with the given value;
- Optional.ofNullable(): Accepts null values, returns an Optional with the given value, or if the value is null, returns an Optional.empty;
- Optional.empty(): Returns an Optional without a value.
Printing the results will show the following output.
Optional[Bob]
Optional[Mary]
Optional.empty
Optional.emptyChecking for Value Presence
Optional provides methods to check if a value is present before accessing it:
Optional<String> name = Optional.ofNullable("Bob");
if (name.isPresent()) {
System.out.println(name.get());
} else {
System.out.println("No name");
}
name.ifPresent(value -> System.out.println(value));
name.ifPresentOrElse(
value -> System.out.println(value),
() -> System.out.println("No name")
);
if (name.isEmpty()) {
System.out.println("It's empty!");
}
- isPresent(): If a value is present, returns true; otherwise, false.
- ifPresent(): If a value is present, executes the given action.
- ifPresentOrElse(): Similar to ifPresent, but has a second parameter that is executed if no value is present.
- isEmpty(): If no value is present, returns true; otherwise, false.
Bob
Bob
BobSetting Default Values
Instead of checking if a value is present, we can define a default value using orElse and orElseGet:
Optional<String> name = Optional.ofNullable(null);
String name1 = name.orElse("Default");
String name2 = name.orElseGet( () -> "We can generate some name" );- orElse(): If a value is present, returns the value; otherwise, returns the default value.
- orElseGet(): If a value is present, returns the value; otherwise, returns the result produced by the supplying function.
Exceptions
Optional<String> name = Optional.ofNullable(null);
name.orElseThrow();There are two ways to use it: with and without parameters.
orElseThrow(): If no value is present, throws NoSuchElementException.
java.util.NoSuchElementException: No value presentname.orElseThrow( () -> new IllegalArgumentException("Value not found") );orElseThrow(Supplier<? extends X> exceptionSupplier): If a value is present, returns the value; otherwise, throws an exception produced by the given exception-supplying function.
java.lang.IllegalArgumentException: Value not foundMap and FlatMap
Optional<String> name = Optional.of("Java");
Optional<String> nameUpperCase = name.map(value -> value.toUpperCase());
Optional<String> nameUpperCaseReference = name.map(String::toUpperCase);map(): Allows transforming the value inside the Optional and returns an Optional with the new value.
Optional<Optional<String>> nestedOptional = Optional.of(nameUpperCaseReference);
Optional<String> regularOptional = nestedOptional.flatMap(op -> op);flatMap(): Used to transform and “flatten” nested Optional instances.
Filtering the values
Optional<String> name = Optional.of("Java");
Optional<String> nameFiltered = name.filter(n -> n.endsWith("va"));filter(): Applies conditions to filter the Optional value.
Conclusion
Optional allows representing the absence of a value explicitly, encouraging better handling of null returns without the need for excessive if checks to avoid null.
When used correctly, Optional improves code maintainability by promoting more functional patterns with map(), flatMap(), orElse(), orElseGet(), and ifPresent(), making the value-handling flow more seamless and readable.
