Kotlin盒装Int不一样 [英] Kotlin boxed Int are not the same

问题描述

请帮助我理解kotlin文档中的这段代码:-

Please help me understand this piece of code in the kotlin docs:-

val a: Int = 10000
print(a === a) // Prints 'true'
val boxedA: Int? = a
val anotherBoxedA: Int? = a
print(boxedA === anotherBoxedA) // !!!Prints 'false'!!!

现在，我了解到首先是int a = 10000，然后在下一行中它是使用===进行比较.

Now, I understand that first int a = 10000 then in the next line it is comparing it using ===.

现在的问题是，为什么分配boxedA=a时使用int?检查它是否为空.可以这样写吗:-

Now the question is why when it assigned boxedA=a, it checked if it is null using int?. Can it just be written like this:-

val boxedA: Int=a

如果我理解错误的方式，请有人指导检查正确的地方或为我解释一下.

Please if I'm understanding it the wrong way, someone guide to check the right place or explain it a bit for me.

推荐答案

在分配boxedA = a时，它使用int?

我不知道你是什么意思.使变量的类型为Int?使其成为可以存储Int或null的变量.这项作业没有检查.如果您要为该变量分配一个非null值，只需将其设为非null即可，而无需输入?类型:

I have no idea what you mean by this. Making a variable have the type Int? makes it a variable that can either store an Int or null. There is no checking happening at this assignment. If you have a non-null value to assign to the variable, just make it non-nullable, without the ? in the type:

val copyOfA: Int = a

您甚至可以省略类型，并推断出Int:

You can even omit the type, and get Int inferred:

val copyOfA = a

---

至于比较:

---

As for the comparisons:

==用于按Kotlin中的值进行比较(这相当于在Java中使用equals)，===用于比较引用(在Java中为==).

== is used for comparing by value in Kotlin (this is the equivalent of using equals in Java), === is used for comparing references (this is == in Java).

创建boxedA和anotherBoxedA时，将在后台创建两个Integer实例(因为可空变量不能用基元表示).与==(它们具有相同的值)相比，它们是相等的，但与===(它们是不同的实例)相比，则不相等.

When you create boxedA and anotherBoxedA, you create two Integer instances under the hood (because nullable variables can't be represented by primitives). These will be equal when compared with == (they have the same value), but not when compared with === (they are different instances).

您可以在此处看到官方文档的相关部分.

You can see the relevant part of the offical docs here.

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