详细来说，Java 中的“foreach”循环是如何工作的？

考虑：

List<String> someList = new ArrayList<>();
// add "monkey", "donkey", "skeleton key" to someList

for (String item : someList) {
    System.out.println(item);
}

相当于什么for循环看起来像不使用for each syntax?

_{People new to Java commonly encounter issues when trying to modify the original data using the new style foreach loop. Use Why doesn't assigning to the iteration variable in a foreach loop change the underlying data? to close duplicates about that common problem. Note that other languages with analogous constructs generally have the same issue; for example, see Why doesn't modifying the iteration variable affect subsequent iterations? for the same issue in Python.}

for (Iterator<String> i = someIterable.iterator(); i.hasNext();) {
    String item = i.next();
    System.out.println(item);
}

请注意，如果您需要使用i.remove();在你的循环中，或者以某种方式访问​​实际的迭代器，你不能使用for ( : )习语，因为实际的迭代器只是推断出来的。

正如 Denis Bueno 所指出的，此代码适用于任何实现Iterable界面.

另外，如果右侧for (:)成语是一个array而不是一个Iterable对象，内部代码使用 int 索引计数器并检查array.length反而。请参阅Java语言规范.