blocks|key|3316568|text|我看到了两个问题(可能还有更多问题)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3316569|1-您的类型参数应该是参数，而不是Int规范。|offset|length|style|CODE|3316570|2-如果要重新分配next的值，那么它需要是一个var。|3316571|case+class+ListNode[T](vl:+T,+nt:+ListNode[T]+=+null)+{+
++++val+value:+T+=+vl
++++var+next:+ListNode[T]+=+nt
}+

scala>+val+a+=+ListNode(1)
a:+ListNode[Int]+=+ListNode(1,null)

scala>+val+b+=+ListNode(2)
b:+ListNode[Int]+=+ListNode(2,null)

scala>+a.next+=+b
a.next:+ListNode[Int]+=+ListNode(2,null)|code-block|syntax|javascript|3316572|当然，作为一个案例类，它可以大大简化。|3316573|//+this+is+all+you+need
case+class+ListNode[T](value:+T,+var+next:+ListNode[T]+=+null)|3316574|entityMap^0|0|H|3|0|9|4|O|3|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@$D|W|E|X|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@$D|Z|E|10|F|G]|$D|11|E|12|F|G]]|9|@]|A|$]]|$1|J|3|K|5|L|7|13|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|14|8|@]|9|@]|A|$]]|$1|Q|3|R|5|L|7|15|8|@]|9|@]|A|$M|N]]|$1|S|3|-4|5|6|7|16|8|@]|9|@]|A|$]]]|T|$]]

I see two problems (there may be more).

1 - Your type parameter should be a parameter not an <code>Int</code> specification.

2 - If you're going to reassign the value of <code>next</code> then it needs to be a <code>var</code>.

<pre><code>case class ListNode[T](vl: T, nt: ListNode[T] = null) { 
 val value: T = vl
 var next: ListNode[T] = nt
} 

scala&gt; val a = ListNode(1)
a: ListNode[Int] = ListNode(1,null)

scala&gt; val b = ListNode(2)
b: ListNode[Int] = ListNode(2,null)

scala&gt; a.next = b
a.next: ListNode[Int] = ListNode(2,null)
</code></pre>

Of course, being a case class, it can be greatly simplified.

<pre><code>// this is all you need
case class ListNode[T](value: T, var next: ListNode[T] = null)
</code></pre>

blocks|key|1447929|text|这是因为您使用的是def，这是一个函数。您可能需要使用vars定义case类。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1447930|下面的代码可以工作，但您可能需要重新考虑可变案例类的整个概念。|1447931|case+class+ListNode[Int](v1:Int,+nt:ListNode[Int]=null)+{
++var+_nt+=+nt
++def+value:+Int+=+v1
++def+next:+ListNode[Int]+=+_nt
++def+next_=(+newNext:ListNode[Int]+)+=+{+_nt+=+newNext+}
}
scala>+val+a+=+ListNode(1,null)
a:+ListNode[Int]+=+ListNode(1,null)

scala>+a.next+=+ListNode(2,null)
a.next:+ListNode[Int]+=+ListNode(2,null)|code-block|syntax|javascript|1447932|请注意，理想的情况是通过复制完成变异案例类：|1447933|scala>+a.copy(+v1=500+)
res0:+ListNode[Int]+=+ListNode(500,null)|1447934|此外，如果某些东西可能是null，您可以考虑将其包装在Option中.但我认为这是一个“踢轮胎”的代码，而不是生产代码:-)。|1447935|entityMap^0|9|3|0|0|0|0|0|C|4|R|6|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|T|$]]

That's because you're using <code>def</code>, which is a function. You might want to define the case class using vars.

The below code will work, but you might want to reconsider the whole idea of mutable case classes.

<pre><code>case class ListNode[Int](v1:Int, nt:ListNode[Int]=null) {
 var _nt = nt
 def value: Int = v1
 def next: ListNode[Int] = _nt
 def next_=( newNext:ListNode[Int] ) = { _nt = newNext }
}
scala&gt; val a = ListNode(1,null)
a: ListNode[Int] = ListNode(1,null)

scala&gt; a.next = ListNode(2,null)
a.next: ListNode[Int] = ListNode(2,null)
</code></pre>

Note that mutating case classes is ideally done via copy:

<pre><code>scala&gt; a.copy( v1=500 )
res0: ListNode[Int] = ListNode(500,null)
</code></pre>

Additionally, if something may be <code>null</code> you can consider wrapping it in an <code>Option</code>... but I assume this is a "kick-the-tires" code, not a production one :-).

blocks|key|3316654|text|Scala中的Case类是不可变的，这意味着您不能更改它们的值。在这种情况下，即使您没有使用case类，next也是一个函数(它是用def定义的)，因此尝试给它赋值是没有意义的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3316655|另外，在Scala中使用null并不是很好的实践。最好使用选项类。有几种方法可以改变代码以解决问题。如果要使用可变类，请考虑以下内容：|3316656|class+ListNode[Int](value:+Int,+nt:+Option[ListNode[Int]]+=+None)+{
++var+next+=+nt
}

object+ListNode+{

++def+apply(value:+Int,+nt:+Option[ListNode[Int]]+=+None)+=+new+ListNode[Int](value,+nt)
}

var+a+=+ListNode(1)

var+b+=+ListNode(2)

a.next+=+Some(b)|code-block|syntax|javascript|3316657|entityMap^0|1G|4|1U|3|0|C|4|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

Case classes in Scala are immutable, which means you can't change their values. In this case, even if you weren't using a case class, <code>next</code> is a function (it is defined with <code>def</code>) so it does not make sense to attempt to assign a value to it.

As an additional point, it is not good practice to use <code>null</code> in Scala. Better to use the Option class. There are several ways to you could alter your code to solve your problem. If you want to use mutable classes, consider the following:

<pre><code>class ListNode[Int](value: Int, nt: Option[ListNode[Int]] = None) {
 var next = nt
}

object ListNode {

 def apply(value: Int, nt: Option[ListNode[Int]] = None) = new ListNode[Int](value, nt)
}

var a = ListNode(1)

var b = ListNode(2)

a.next = Some(b)
</code></pre>

me again, newbie to scala and downvote is welcome if this question is stupid to you...

ok, I have a case class called "ListNode", and below is the error I got:

<pre><code>scala&gt; case class ListNode[Int](vl: Int, nt: ListNode[Int] = null) {
 | def value: Int = vl
 | def next: ListNode[Int] = nt
 | }
defined class ListNode

scala&gt; var a = ListNode(1)
a: ListNode[Int] = ListNode(1,null)

scala&gt; var b = ListNode(2)
b: ListNode[Int] = ListNode(2,null)

scala&gt; a.next = b
&lt;console&gt;:11: error: value next_= is not a member of ListNode[Int]
 a.next = b
 ^
</code></pre>

I've read <a href="https://stackoverflow.com/questions/31255688/scala-value-is-not-a-member-of-int">this</a> and <a href="https://stackoverflow.com/questions/24681777/scala-value-is-not-a-member-of-int">this</a> and <a href="https://stackoverflow.com/questions/18236825/diagnosing-scala-compile-error-value-to-is-not-a-member-of-int">this</a> and <a href="https://stackoverflow.com/questions/18008533/scala-how-to-go-resolve-value-is-not-a-member-of-nothing-error">this</a> and <a href="https://stackoverflow.com/questions/25163255/still-have-error-value-copy-is-not-a-member-of-nothing-even-i-filter-nothing-c">this</a>, but still not really understand what it means...

Why cannot I just set the node next to be another node, just like in Java?

Thank you very much.

scala: value is not a member of ListNode[Int]

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我再说一遍，如果这个问题对你来说很愚蠢的话，欢迎新手来斯卡拉投票.好的，我有一个名为"ListNode“的case类，下面是我得到的错误：scala> case class ListNode[Int](vl: Int, nt: ListNode[Int] = null) {     |     def value: I...

问scala: value不是ListNode[Int]的成员
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问scala: value不是ListNode[Int]的成员EN