Val表示不可变，var表示可变

您可以将val视为Java编程语言的final key world或c++语言的const key world。

简单来说:

var = 变量

Val =变量+ final

val表示不可变，var表示可变

解释一下，“val表示值，var表示变量”。

A distinction that happens to be extremely important in computing (because those two concepts define the very essence of what programming is all about), and that OO has managed to blur almost completely, because in OO, the only axiom is that "everything is an object". And that as a consequence, lots of programmers these days tend not to understand/appreciate/recognize, because they have been brainwashed into "thinking the OO way" exclusively. Often leading to variable/mutable objects being used like everywhere, when value/immutable objects might/would often have been better.

在javascript方面，它与

val -> const 是 -> 是

Val值是类型存储常量。一旦创建它的价值不能重新分配。可以用关键字val定义一个新值。

如。val x: Int = 5

这里type是可选的，因为scala可以从赋值推断它。

变量是类型化的存储单元，只要保留内存空间，就可以再次为其赋值。

如。var x: Int = 5

一旦不再需要存储在这两个存储单元中的数据，JVM就会自动取消对它们的分配。

在scala中，值比变量更受欢迎，因为它们给代码带来了稳定性，尤其是在并发和多线程代码中。

区别在于var可以被重新赋值，而val则不能。可变性，或其他任何实际分配的东西，是一个次要问题:

import collection.immutable
import collection.mutable
var m = immutable.Set("London", "Paris")
m = immutable.Set("New York") //Reassignment - I have change the "value" at m.

而:

val n = immutable.Set("London", "Paris")
n = immutable.Set("New York") //Will not compile as n is a val.

因此:

val n = mutable.Set("London", "Paris")
n = mutable.Set("New York") //Will not compile, even though the type of n is mutable.

如果您正在构建一个数据结构，并且它的所有字段都是val，那么该数据结构因此是不可变的，因为它的状态不能改变。