java – Doubt using Optional

Question:

I'm trying to use this optional class to get the data with null, but it returns an error.

In the main class, I use for with this method. Profession and composition of people.

for(Pessoa p : pessoas) {

        Optional<Profissao> temNome = p.profissao.getNomeP();

If used as a String

Optional<String> temNome =Optional.ofNullable(p.profissao.getNomeP());

works, but I didn't understand the difference

Answer:

Hi!

It seems to me, you're confusing. See, you're accessing the profession name, a string, and you're expecting it to return the parent object, profession.

for(Pessoa p : pessoas) {
   Optional<Profissao> temNome = p.profissao.getNomeP();
   ...
}

The right thing here would be:

for(Pessoa p : pessoas) {
   Optional<Profissao> possivelProfissao = Optional.ofNullable(p.profissao);
   possivelProfissao.ifPresent( profissao -> System.out.println(p.getNomeP()) );
   ...
}

Or:

for(Pessoa p : pessoas) {
   Optional<Profissao> possivelProfissao = Optional.ofNullable(p.profissao);
   if(possivelProfissao.isPresent()){
      String nome = possivelProfissao.get().getNomeP();
      System.out.println(nome );
   }
   ...
}

I recommend reading this article by Caelum . It gives a nice foundation. The documentation , although very complete, will not be very didactic Any doubts, just ask.

Edition 01

If you want to return a standard String when there is no profession, you can do something like this:

public String temNome(Profissao profissao) {
  return Optional.ofNullable(profissao.getNomeP()).orElse("Nao tem Profissao");
}

The coolest thing is that you do it in your person class, writing a getNameProfessional(), like this:

public class Pessoa{
   ...
   public String getNomeProfissao(){
      return Optional.ofNullable(this.profissao.getNomeP()).orElse("Nao tem Profissao");
   }
   ...
}

This way you will follow the Law of Demeter, and you will not chain calls.