我有这两个代码示例：

代码A：

Stream aStream = firstLevelList.stream()

.flatMap(firstLevelElement -> firstLevelElement.getSecondLevelList().stream()

.flatMap(secondLevelElement -> secondLevelElement.getThirdLevelList().stream()

.map(thirdLevelElement -> thirdLevelElement.toString())));

代码B：

Stream aStream = firstLevelList.stream()

.flatMap(firstLevelElement -> firstLevelElement.getSecondLevelList().stream())

.flatMap(secondLevelElement -> secondLevelElement.getThirdLevelList().stream())

.map(thirdLevelElement -> thirdLevelElement.toString());

两者都有完全相同的结果,这是最好的实现？为什么？

最佳答案 选项1

以下内容读得很好,感觉更常见：

firstLevelList.stream()

.flatMap(firstLevelElement -> firstLevelElement.getSecondLevelList().stream())

.flatMap(secondLevelElement -> secondLevelElement.getThirdLevelList().stream())

.map(Object::toString);

它避免了@Holger指出的嵌套,这对读者来说很重要.

选项2

或者,如果它与代码库样式的其余部分不相符,我们可以使用不同的缩进来进行嵌套：

firstLevelList.stream().flatMap(

firstLevelElement -> firstLevelElement.getSecondLevelList().stream().flatMap(

secondLevelElement -> secondLevelElement.getThirdLevelList().stream().map(Object::toString)

)

);

选项3

如果它仍然感觉太神秘,我们可以提取变量或方法来命名不同的流：

firstLevelList.stream().flatMap(

firstLevelElement -> firstLevelElement.getSecondLevelList().stream().flatMap(

secondLevelElement -> getThirdLevelStream(secondLevelElement)

)

);

Stream getThirdLevelStream(SecondLevelElement secondLevelElement) {

return secondLevelElement.getThirdLevelList().stream().map(Object::toString);

}

选项4

我们可以将这些方法移动到现在关注Law of Demeter的元素类：

firstLevelList.stream().flatMap(FirstLevelElement::getSecondLevelStream);

class FirstLevelElement {

Stream getSecondLevelStream() {

return this.getSecondLevelList().stream().flatMap(SecondLevelElement::getThirdLevelStream);

}

Collection getSecondLevelList() {...}

}

class SecondLevelElement {

Stream getThirdLevelStream() {

return this.getThirdLevelList().stream().map(Object::toString);

}

Collection getThirdLevelList() {...}

}

如果在方法中的其他地方重用流方法,这将添加一些值.

结论

关于哪些选项更好,可以提出不同的论点.一般来说,它们都非常好.