我在使用 Java 8“可选”容器时遇到了一个乏味的问题。我无法将可选映射到“冒泡”另一个可选。
假设我有一个 RussianNestingDoll 类
public class NestedOptionalTest {
public static void main(String[] args) {
RussianNestingDoll doll = RussianNestingDoll.createInstance(RussianNestingDoll.createInstance(RussianNestingDoll.createInstance()));
Optional<Optional<RussianNestingDoll>> thirdDollContents = doll.getInnerDoll().map(d -> d.getInnerDoll());
if (thirdDollContents.isPresent() && thirdDollContents.get().isPresent()) {
System.out.println(thirdDollContents.get().get());
}
else {
System.out.println("empty");
}
}
private static final class RussianNestingDoll {
private final Optional<RussianNestingDoll> innerDoll;
public Optional<RussianNestingDoll> getInnerDoll() {
return innerDoll;
}
private RussianNestingDoll(Optional<RussianNestingDoll> innerDoll) {
this.innerDoll = innerDoll;
}
public static RussianNestingDoll createInstance() {
return new RussianNestingDoll(Optional.empty());
}
public static RussianNestingDoll createInstance(RussianNestingDoll innerDoll) {
return new RussianNestingDoll(Optional.of(innerDoll));
}
}
}
最好不要使用嵌套的可选值,而是只使用可选的“冒泡”。这样我就可以只调用一次“isPresent()”和“get()”,而不是同时调用它们两次。有什么办法可以做到这一点?
最佳答案
我不太确定你想要什么,但你可以像这样重写你的代码:
RussianNestingDoll doll = RussianNestingDoll.get(RussianNestingDoll.get(RussianNestingDoll.get()));
String content = doll.getInnerDoll()
.flatMap(d -> d.getInnerDoll())
.map(d -> d.get().toString())
.orElse("empty");
System.out.println(content);
如果你之后想使用娃娃:
Optional<RussianNestingDoll> thirdDoll = doll.getInnerDoll()
.flatMap(d -> d.getInnerDoll());
if (thirdDoll.isPresent()) {
System.out.println(thirdDoll.get());
}
else {
System.out.println("empty");
}
关于java - 映射嵌套可选?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/28613028/