Java 8 可选——如何处理嵌套的对象结构

Question

是否有任何简单的方法来减少代码行以使用 Optional 作为以下代码的替代来打印最内层的非 null 对象。我觉得我们现在必须编写更多代码行来避免空值检查。

在 Java 8 中有什么简单的方法可以使这段代码变得简短而有趣吗？

import java.util.Optional;

public class OptionalInnerStruct {

public static void main(String[] args) {

    // creepy initialization step, dont worry
    Employee employee = new Employee();
    employee.setHuman(Optional.empty());

    // with optional
    Optional<Human> optionalHuman = employee.getHuman();
    if (optionalHuman.isPresent()) {
        Human human = optionalHuman.get();
        Optional<Male> optionalMale = human.getMale();
        if (optionalMale.isPresent()) {
            Male male = optionalMale.get();
            Optional<Integer> optionalAge = male.getAge();
            if (optionalAge.isPresent()) {
                System.out.println("I discovered the variable finally " + optionalAge.get());
            }

        }

    }

    // without optional in picture, it will be something like:
    /*if(null! = employee.getHuman() && null!= employee.getHuman().getMale() && null! = employee.getHuman().getMale().getAge()) {
        System.out.println("So easy to find variable " + employee.getHuman().getMale().getAge());
    }*/
}

static class Employee {

    Optional<Human> human;

    public Optional<Human> getHuman() {
        return human;
    }

    public void setHuman(Optional<Human> human) {
        this.human = human;
    }
}

class Human {
    Optional<Male> male;

    public Optional<Male> getMale() {
        return male;
    }

    public void setMale(Optional<Male> male) {
        this.male = male;
    }
}

class Male {
    Optional<Integer> age;

    public Optional<Integer> getAge() {
        return age;
    }

    public void setAge(Optional<Integer> age) {
        this.age = age;
    }
}
}

Answer 1

您可以使用 Optional.flatMap这里

employee.getHuman()
        .flatMap(Human::getMale)
        .flatMap(Male::getAge)
        .ifPresent(age -> System.out.println("I discovered the variable finally " + age);