问题描述
我不确定Kotlin中IntArray和Array<Int>之间的区别是什么，为什么不能互换使用它们:
I'm not sure what the difference between an IntArray and an Array<Int> is in Kotlin and why I can't used them interchangeably:
我知道在定位JVM时IntArray会转换为int[]，但是Array<Int>会转换为什么?
I know that IntArray translates to int[] when targeting the JVM, but what does Array<Int> translate to?
此外，您还可以拥有String[]或YourObject[].为什么Kotlin拥有{primitive}Array类型的类，而几乎所有的东西都可以排列成数组，而不仅是图元.
Also, you can also have String[] or YourObject[]. Why Kotlin has classes of the type {primitive}Array when pretty much anything can be arranged into an array, not only primitives.
推荐答案
Array<Int>是引擎盖下的Integer[]，而IntArray是int[].就是这样.
Array<Int> is an Integer[] under the hood, while IntArray is an int[]. That's it.
这意味着，当将Int放入Array<Int>时，将始终装箱(特别是使用Integer.valueOf()调用).在IntArray的情况下，不会进行装箱，因为它会转换为Java基本数组.
This means that when you put an Int in an Array<Int>, it will always be boxed (specifically, with an Integer.valueOf() call). In the case of IntArray, no boxing will occur, because it translates to a Java primitive array.
除了上面提到的可能的性能含义外，还可以考虑其他一些便利.原始数组可以保留未初始化的状态，并且在所有索引处都具有默认的0值.这就是为什么IntArray和其他原始数组的构造函数仅采用size参数的原因:
Other than the possible performance implications of the above, there's also convenience to consider. Primitive arrays can be left uninitialized and they will have default 0 values at all indexes. This is why IntArray and the rest of the primitive arrays have constructors that only take a size parameter:
val arr = IntArray(10)
println(arr.joinToString()) // 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
相反，Array<T>没有只采用size参数的构造函数:创建后，在所有索引上都需要有效的非null T实例以使其处于有效状态.对于Number类型，这可能是默认的0，但是无法创建任意类型T的默认实例.
In contrast, Array<T> doesn't have a constructor that only takes a size parameter: it needs valid, non-null T instances at all indexes to be in a valid state after creation. For Number types, this could be a default 0, but there's no way to create default instances of an arbitrary type T.
因此，在创建Array<Int>时，您也可以使用带有初始化函数的构造函数:
So when creating an Array<Int>, you can either use the constructor that takes an initializer function as well:
val arr = Array<Int>(10) { index -> 0 } // full, verbose syntax
val arr = Array(10) { 0 } // concise version
或者创建一个Array<Int?>以避免必须初始化每个值，但是随后您每次从数组中读取数据时都会被迫处理可能的null值.
Or create an Array<Int?> to avoid having to initialize every value, but then you'll be later forced to deal with possible null values every time you read from the array.
val arr = arrayOfNulls<Int>(10)
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