Optional get value if present

问题

As an example I have an optional like this:

Optional<Desktop> opt = Optional.ofNullable(status).map(Status::getDesktop);

I want to have the desktop and work with it outside of lambda expressions. I do it like this:

if (opt.isPresent()){
    Desktop desktop = opt.get();
    ...
}

Is there a better solution to get the desktop; something like this ?

Desktop desktop = Optional.ofNullable(status).map(Status::getDesktop).ifPresent(get());

EDIT: OrElse was the method I was looking for :)

回答1:

If you have a default value for your Desktop, you could try with Optional.orElse:

Desktop defaultDesktop = ...;

Desktop desktop = Optional.ofNullable(status)
    .map(Status::getDesktop)
    .orElse(defaultDesktop);

However, you don't have to necessarily work inside a lambda expression with Optional.ifPresent. You could perfectly use a method that receives a Desktop instance, which would act as the Consumer argument of Optional.ifPresent:

Desktop desktop = Optional.ofNullable(status)
    .map(Status::getDesktop)
    .ifPresent(this::workWithDesktop);

Then:

void workWithDesktop(Desktop desktop) {
    // do whatever you need to do with your desktop
}

If you need additional arguments (apart from the desktop itself), you could use a lambda expression that invokes the method instead:

String arg1 = "hello";
int arg2 = 10;

Desktop desktop = Optional.ofNullable(status)
    .map(Status::getDesktop)
    .ifPresent(desktop -> this.workWithDesktop(desktop, arg1, arg2));

And then:

void workWithDesktop(Desktop desktop, String arg1, int arg2) {
    // do whatever you need to do with your desktop, arg1 and arg2
}

回答2:

I was told here just last week that it's a code smell to even use Optional like this at all, so

Desktop desktop = (status != null)? status.getDesktop() : null;

来源：https://stackoverflow.com/questions/47834804/optional-get-value-if-present

标签

java

lambda

optional