This optional class was launched in Java 8 to steer clear of null checks and NullPointersException Issues. Three new methods are added in Java 9 to enhance its functionality.
Syntax
public Stream<T> stream()
If a value is available, it goes back on a sequential Stream having only that value, otherwise goes back on an empty Stream.
Example
import java.util.Arrays; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; import java.util.stream.Stream; public class Tester { public static void main(String[] args) { List<Optional<String>> list = Arrays.asList ( Optional.empty(), Optional.of("A"), Optional.empty(), Optional.of("B")); //filter the list based to print non-empty values //if optional is non-empty, get the value in stream, otherwise return empty List<String> filteredList = list.stream() .flatMap(o -> o.isPresent() ? Stream.of(o.get()) : Stream.empty()) .collect(Collectors.toList()); //Optional::stream method will return a stream of either one //or zero element if data is present or not. List<String> filteredListJava9 = list.stream() .flatMap(Optional::stream) .collect(Collectors.toList()); System.out.println(filteredList); System.out.println(filteredListJava9); } }
Output
[A, B] [A, B]
Syntax
public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction)
If a value is available, perform the given task with the value, and if not then perform the given empty-based task.
Example
import java.util.Optional; public class Tester { public static void main(String[] args) { Optional<Integer> optional = Optional.of(1); optional.ifPresentOrElse( x -> System.out.println("Value: " + x),() -> System.out.println("Not Present.")); optional = Optional.empty(); optional.ifPresentOrElse( x -> System.out.println("Value: " + x),() -> System.out.println("Not Present.")); } }
Output
Value: 1 Not Present.
Syntax
public Optional<T> or(Supplier<? extends Optional<? extends T>> supplier)
If a value is available, goes back on an Optional defining the value, and if not then goes back on an Optional generated by the supplying function.
Example
import java.util.Optional; import java.util.function.Supplier; public class Tester { public static void main(String[] args) { Optional<String> optional1 = Optional.of("Mahesh"); Supplier<Optional<String>> supplierString = () -> Optional.of("Not Present"); optional1 = optional1.or( supplierString); optional1.ifPresent( x -> System.out.println("Value: " + x)); optional1 = Optional.empty(); optional1 = optional1.or( supplierString); optional1.ifPresent( x -> System.out.println("Value: " + x)); } }
Output
Value: Mahesh Value: Not Present