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Languages with well-integrated support for closures (such as Scala, Smalltalk, and Ruby) usually provide support for looping over their collections using internal iterators - they are, after all, easier to use in most cases - while other object-oriented languages (such as C++, Java, and C#) tend to use external iterators. Without well-integrated language support for closures, internal iterators would be too painful to use effectively. For that reason, the Java collection framework uses external iterators. But once we have closures in the language, wouldn't it be worth reversing that decision?