Java的for-each是否为每次迭代都调用嵌入式方法(返回集合)? [英] Does Java's for-each call an embedded method (that returns the collection) for every iteration?

问题描述

如果有方法调用MyClass.returnArray()，并且我使用for-each构造(也称为"enhanced for"循环)遍历数组:

If there is a method call MyClass.returnArray() and I iterate over the array using the for-each construct (also called the "enhanced for" loop):

for (ArrayElement e : MyClass.returnArray()) {
   //do something
}

然后每次迭代都会调用returnArray()方法吗?

will then the returnArray() method be called for every iteration?

推荐答案

否，不会.第一次调用的结果将存储在编译后的代码中的一个临时变量中.

No, it won't. The result of the first call will be stored in the compiled code in a temporary variable.

来自有效的Java 2nd.编.，第46项:

请注意，使用此功能不会降低性能 for-each循环，即使对于数组也是如此.实际上，它可能会提供一点性能优势 在某些情况下，通过普通的for循环，因为它计算了 数组索引仅一次.

Note that there is no performance penalty for using the for-each loop, even for arrays. In fact, it may offer a slight performance advantage over an ordinary for loop in some circumstances, as it computes the limit of the array index only once.

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