Java 9 - java.util.Optional Improvements

(1) ifPresentOrElse(Consumer, Runnable)

This new method performs the given Consumer action if a value is present, otherwise runs the given Runnable action.

 IntStream.of(1, 2, 4)
          .filter(i -> i % 3 == 0)
          .findFirst()
          .ifPresentOrElse(System.out::println, () -> {
              System.out.println("No multiple of 3 found");
          });

 No multiple of 3 found

 IntStream.of(2, 6, 8)
          .filter(i -> i % 3 == 0)
          .findFirst()
          .ifPresentOrElse(System.out::println, () -> {
              System.out.println("No multiple of 3 found");
          });

 6

Comparing with Java 8 Optional.isPresent():

 OptionalInt opt = IntStream.of(1, 2, 4)
                            .filter(i -> i % 3 == 0)
                            .findFirst();
 if (opt.isPresent()) {
     System.out.println(opt.getAsInt());
 } else {
     System.out.println("No multiple of 3 found");
 }

 No multiple of 3 found

Comparing with Java 8 Optional.ifPresent():

ifPresent() method does not provide an alternative action when the value is absent:

 IntStream.of(1, 2, 4)
          .filter(i -> i % 3 == 0)
          .findFirst()
          .ifPresent(System.out::println);

Comparing with Java 8 Optional.orElse():

All above cases are action based. For a result assignment, we can still use orElse() method when the value is not present.

 int result = IntStream.of(1, 2, 4)
                       .filter(i -> i % 3 == 0)
                       .findFirst()
                       .orElse(-1);
 System.out.println(result);

 -1

(2) Optional.or(Supplier)

The new method can be used to lazily produce an Optional via a Supplier when the value is not present:

 char digit = Stream.of('a', 'b', 'c')
                    .filter(c -> Character.isDigit(c))
                    .findFirst()
                    .or(() -> Optional.of('0')).get();
 System.out.println(digit);

 0

Note that or methods are not added to OptionalInt, OptionalLong and OptionalDouble classes in Java 9.

Comparing with orElseGet()

The Java 8 Optional.orElseGet() method produces a 'value' if it is not present, whereas, or method returns an instance of Optional if value is not present. Following is an example of orElseGet() method:

 char result = Stream.of('a', 'b', 'c')
                    .filter(c -> Character.isDigit(c))
                    .findFirst()
                    .orElseGet(()->'0');
 System.out.println(result);

 0

(3) Optional.stream()

This new method returns a Stream containing only one element returned by this Optional. If the value is not present then an empty Stream is return:

 OptionalInt opt1 = IntStream.of(2, 5, 6).max();
 OptionalInt opt2 = IntStream.of(1, 3, 7).max();
 IntStream.concat(opt1.stream(), opt2.stream())
          .forEach(System.out::println);

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