Review

Uses Optional.get() without prior check of isPresent() within Optional.map(), which may cause a NullPointerException. Safe way is to use flatMap instead, which takes care of potential null values.

• missing/call
• superfluous/call

com/xpinjection/java8/misused/optional/HundredAndOneApproach.java

getPersonCarInsuranceName(Person)

class HundredAndOneApproach.SameOldImperativeStyle {
        public String getPersonCarInsuranceName(Person person) {
            String name = "Unknown";
            if (ofNullable(person).isPresent()) {
                if (person.getCar().isPresent()) {
                    if (person.getCar().get().getInsurance().isPresent()) {
                        name = person.getCar().get().getInsurance().get().getName();
                    }
                }
            }
            return name;
        }
}

class HundredAndOneApproach.UsingIfPresentInSameImperativeWayWithDirtyHack {
        public String getPersonCarInsuranceName(Person person) {
            final StringBuilder builder = new StringBuilder();
            ofNullable(person).ifPresent(
                    p -> p.getCar().ifPresent(
                            c -> c.getInsurance().ifPresent(
                                    i -> builder.append(i.getName())
                            )
                    )
            );
            return builder.toString();
        }
}

class HundredAndOneApproach.UsingMapWithUncheckedGet {
        public String getPersonCarInsuranceName(Person person) {
            return ofNullable(person)
                    .map(Person::getCar)
                    .map(car -> car.get().getInsurance())
                    .map(insurance -> insurance.get().getName())
                    .orElse("Unknown");
        }
}

class HundredAndOneApproach.UsingMapWithOrElseEmptyObjectToFixUncheckedGet {
        public String getPersonCarInsuranceName(Person person) {
            return ofNullable(person)
                    .map(Person::getCar)
                    .map(car -> car.orElseGet(Car::new).getInsurance())
                    .map(insurance -> insurance.orElseGet(Insurance::new).getName())
                    .orElse("Unknown");
        }

}

class UsingFlatMap {
    public String getCarInsuranceNameFromPersonUsingFlatMap(Person person) {
        return ofNullable(person)
                .flatMap(Person::getCar)
                .flatMap(Car::getInsurance)
                .map(Insurance::getName)
                .orElse("Unknown");
    }
}