Java 9 - Optional Class Improvements

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Optional Class was introduced in Java 8 to avoid null checks and NullPointerException issues. In java 9, three new methods are added to improve its functionality.

  • stream()
  • ifPresentOrElse()
  • or()

stream() method

Syntax

public Stream<T> stream()

If a value is present, it returns a sequential Stream containing only that value, otherwise returns 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]

ifPresentOrElse() method

Syntax

public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction)

If a value is present, performs the given action with the value, otherwise performs the given empty-based action.

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.

or() method

Syntax

public Optional<T> or(Supplier<? extends Optional<? extends T>> supplier)

If a value is present, returns an Optional describing the value, otherwise returns an Optional produced 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
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