Java 9 Improved Optional Class

Java 9 New Features

The Optional class was introduced in Java 8 and has been effective in handling null pointer exceptions. In Java 9, three methods have been added to enhance its functionality:

stream()
ifPresentOrElse()
or()

stream() Method

Syntax

public Stream<T> stream()

The stream method converts an Optional into a Stream. If the Optional contains a value, it returns a Stream containing that value; otherwise, it returns an empty Stream (Stream.empty()).

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 to print non-empty values

      // If the optional is non-empty, get the value in the stream, otherwise return an empty stream
      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 elements 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);
   }
}

Execution output:

[A, B]
[A, B]

ifPresentOrElse() Method

Syntax

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

The ifPresentOrElse method includes an "else" clause, accepting two parameters: a Consumer and a Runnable.

The purpose of the ifPresentOrElse method is to call the function action with the contained value if the Optional contains a value, i.e., action.accept(value), which is consistent with ifPresent. The difference from ifPresent is the second parameter, emptyAction — if the Optional does not contain a value, ifPresentOrElse will call emptyAction, i.e., emptyAction.run().

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."));
   }
}

System.out.println("Not Present.");

optional = Optional.empty();

optional.ifPresentOrElse(x -> System.out.println("Value: " + x), () -> System.out.println("Not Present."));
}
}

Execution 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));  
   }  
}

Execution output:

Value: Mahesh
Value: Not Present

Java 9 New Features ```

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