Java 9, 10, 11 Optional API news overview.

Reference: http://iteratrlearning.com/java9/2016/09/05/java9-optional.html

• public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction) - it is a way of simplifying such task:

  Optional<Person> person = get(...);
  if (person.isPresent()) {
      render(person.get());
  } else {
      renderEmpty();
  }
  

  just to:

  get(...).ifPresentOrElse(X::render, X::renderEmpty)
  

• public Optional<T> or(Supplier<? extends Optional<? extends T>> supplier) - it is a way of simplifying:

  assumptions:

  Optional<Person> findByName(...)
  Optional<Person> findById(...)
  

  then something like this:

  Optional<Person> person = 
      Optional.ofNullable(
          findByName(person.getName())
          .orElseGet(() -> findById(person.getId())
      ));
  

  could be rewritten just to:

  Optional<Person> person = 
              findByName(person.getName())
              .or(() -> findById(person.getId());
  

• public Stream<T> stream() - please refer my other github project: java-converting-optionals-list

• public T orElseThrow() - exact copy of get() but with more meaningful name:

  • get()

    public T get() {
        if (value == null) {
            throw new NoSuchElementException("No value present");
        }
        return value;
    }    
    

  • orElseThrow()

    public T orElseThrow() {
        if (value == null) {
            throw new NoSuchElementException("No value present");
        }
        return value;
    }    
    

  Remark: https://twitter.com/briangoetz/status/665239052380012548?lang=en

  In hindsight, calling it get was a (my) mistake. Just too easy to call get() w/o thinking.

  @BrianGoetz

  Remark: get() will be deprecated: http://mail.openjdk.java.net/pipermail/core-libs-dev/2016-April/040531.html

• public boolean isEmpty() ~ !isPresent()
  • isPresent()

    public boolean isPresent() {
            return value != null;
    }
    

  • isEmpty()

    public boolean isEmpty() {
        return value == null;
    }
    

We provide tests for mentioned above methods.