Java“for each"循环是如何工作的? [英] How does the Java 'for each' loop work?

问题描述

考虑:

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

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

如果不使用 for each 语法，等效的 for 循环会是什么样子?

What would the equivalent for loop look like without using the for each syntax?

推荐答案

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

请注意，如果您需要在循环中使用 i.remove(); 或以某种方式访问​​实际迭代器，则不能使用 for ( : ) 习惯用法，因为实际的迭代器只是推断出来的.

Note that if you need to use i.remove(); in your loop, or access the actual iterator in some way, you cannot use the for ( : ) idiom, since the actual iterator is merely inferred.

正如丹尼斯·布埃诺 (Denis Bueno) 所指出的，此代码适用于实现 Iterable 接口.

As was noted by Denis Bueno, this code works for any object that implements the Iterable interface.

此外，如果 for (:) 习惯用法的右侧是 array 而不是 Iterable 对象，则内部code 使用 int 索引计数器并检查 array.length 代替.请参阅 Java 语言规范.

Also, if the right-hand side of the for (:) idiom is an array rather than an Iterable object, the internal code uses an int index counter and checks against array.length instead. See the Java Language Specification.

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