Optional is a container class introduced in Java 8 that represents an object that may or may not contain a non-null value. It is primarily used to avoid NullPointerException and provide a more elegant way to handle null values. Here are some common usage examples of Optional.
Creating Optional objects
Optional.of(value): Creates an Optional object containing a non-null value.
Optional.ofNullable(value): Creates an Optional object that may contain a null value.
Optional.empty(): Creates an empty Optional object.
Checking if Optional contains a value
isPresent(): Returns true if the Optional contains a value.
ifPresent(Consumer<? super T> action): Performs the given action if the Optional contains a value.
Getting the value of Optional
get(): Returns the value if the Optional contains a value, otherwise throws NoSuchElementException.
orElse(T other): Returns the value if the Optional contains a value, otherwise returns the default value.
orElseGet(Supplier<? extends T> other): Returns the value if the Optional contains a value, otherwise calls the Supplier and returns its result.
orElseThrow(Supplier<? extends X> exceptionSupplier): Returns the value if the Optional contains a value, otherwise throws the exception provided by the Supplier.
Transforming the value of Optional
map(Function<? super T, ? extends U> mapper): Applies the mapping function and returns a new Optional if the Optional contains a value.
flatMap(Function<? super T, Optional<U>> mapper): Similar to map, but the mapping function returns an Optional and does not nest Optional.
Example
import java.util.Optional;
public class OptionalExamples {
public static void main(String[] args) {
// Create Optional objects
Optional<String> nonEmptyOptional = Optional.of("Hello, World!");
Optional<String> nullableOptional = Optional.ofNullable(null);
Optional<String> emptyOptional = Optional.empty();
// Check if Optional contains a value
System.out.println("nonEmptyOptional is present: " + nonEmptyOptional.isPresent());
System.out.println("nullableOptional is present: " + nullableOptional.isPresent());
System.out.println("emptyOptional is present: " + emptyOptional.isPresent());
// Get the value of Optional
System.out.println("nonEmptyOptional value: " + nonEmptyOptional.get());
System.out.println("nullableOptional value or default: " + nullableOptional.orElse("Default Value"));
System.out.println("emptyOptional value or default: " + emptyOptional.orElse("Default Value"));
// Perform an action using ifPresent
nonEmptyOptional.ifPresent(value -> System.out.println("Value is present: " + value));
// Transform the value of Optional
Optional<Integer> lengthOptional = nonEmptyOptional.map(String::length);
System.out.println("Length of nonEmptyOptional value: " + lengthOptional.orElse(0));
// Handle nested Optional using flatMap
Optional<Optional<String>> nestedOptional = Optional.of(Optional.of("Nested Value"));
Optional<String> flatMappedValue = nestedOptional.flatMap(opt -> opt);
System.out.println("FlatMapped value: " + flatMappedValue.orElse("No Value"));
}
}