blocks|key|3137261|text|我是scala.collection.mutable的ArrayBuffer。您可以找到scaladoc+here。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3137262|entityMap|0|LINK|mutability|MUTABLE|url|http://www.scala-lang.org/api/current/scala/collection/mutable/ArrayBuffer.html^0|2|O|R|B|1H|4|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

It's <code>ArrayBuffer</code> from <code>scala.collection.mutable</code>. You can find the scaladocs <a href="http://www.scala-lang.org/api/current/scala/collection/mutable/ArrayBuffer.html" rel="noreferrer">here</a>.

blocks|key|2923229|text|很难说你应该做什么，因为你还没有说你有兴趣使用ArrayList的什么行为。从您想要利用哪些scala特性的角度考虑会更有用。这里有一个很好的解释：http://grahamhackingscala.blogspot.com/2010/02/how-to-convert-java-list-to-scala-list.html。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2923230|也就是说，您可能需要某种IndexedSeq。|2923231|entityMap|0|LINK|mutability|MUTABLE|url|http://grahamhackingscala.blogspot.com/2010/02/how-to-convert-java-list-to-scala-list.html^0|N|9|22|2I|0|0|C|A|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|G|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

It's hard to say exactly what you should do because you haven't said what behavior of <code>ArrayList</code> you're interested in using. It's more useful to think in terms of which scala traits you want to take advantage of. Here's a good explanation: <a href="http://grahamhackingscala.blogspot.com/2010/02/how-to-convert-java-list-to-scala-list.html" rel="nofollow">http://grahamhackingscala.blogspot.com/2010/02/how-to-convert-java-list-to-scala-list.html</a>.

That said, you probably want some sort of <code>IndexedSeq</code>.

blocks|key|244886|text|我可以想出3个更具体的问题来回答你的问题：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|244887|什么是Scala的默认collection?|244888|What+Scala集合，具有与ArrayList|unordered-list-item|offset|length|style|CODE|244889|
|244890|What's相似的特征，是Scala中Array的一个很好的替代品？|244891|244892|以下是这些问题的答案：|244893|Scala的默认集合是什么？|244894|Seq是Scala的List接口的等价物。还有一个更通用的接口，那就是GenSeq+--主要区别在于GenSeq可以串行或并行地处理操作，具体取决于实现。|244895|因为Scala允许程序员将Seq用作工厂，所以他们通常不会费心定义特定的实现，除非他们关心它。当他们这样做时，他们通常会选择Scala的List或Vector。它们都是不可变的，并且Vector具有很好的索引访问性能。另一方面，List在它擅长的操作中做得非常好。|244896|哪个Scala集合具有类似于ArrayList的特征|244897|那应该是scala.collection.mutable.ArrayBuffer。|244898|在Scala中，什么是Array的好替代品？|244899|好消息是，你可以在Scala中直接使用Array！在Java语言中，通常会避免使用Array，因为它通常与泛型不兼容。它是一个协变集合，而泛型是不变的，它是可变的--这使得它的协变是危险的，它接受泛型不能接受的原语，并且它的方法集非常有限。|244900|在Scala中，Array是不变的--它仍然是与Java中相同的Array，这使得大多数问题消失。Scala接受AnyVal+(相当于原语)作为其“泛型”的类型，即使它会进行自动装箱。通过“丰富我的库”模式，所有Seq方法的都可用于Array。|BOLD|244901|因此，如果您想要更强大的Array，只需使用Array即可。|244902|一个缩水和增长的集合呢？|244903|所有集合可用的默认方法都会生成新的集合。例如，如果我这样做：|244904|val+ys+=+xs+filter+(x+=>+x+%25+2+==+0)|code-block|syntax|javascript|244905|那么ys将是一个新的集合，而xs仍将与此命令之前相同。无论xs是什么：Array、List等等，这都是正确的。|244906|当然，这是有代价的--毕竟，您正在生成一个新的集合。Scala的不可变集合在处理这种开销方面要好得多，因为它们是持久化的，但这取决于执行什么操作。|244907|任何集合都不能对filter做太多的事情，但是List在生成新集合时有很好的性能，可以通过在元素前面加上一个元素或者去掉头部--事实上，这是堆栈的基本操作。Vector在许多操作上都有很好的性能，但只有在集合不小的情况下，它才能获得回报。例如，对于多达100个元素的集合，总成本可能超过收益。|244908|因此，您实际上可以向Array添加或删除元素，Scala将为您生成一个新的Array，但当您这样做时，您将支付完整副本的成本。|244909|Scala可变集合添加了一些其他方法。具体地说，可以增加或减少大小的集合实现了Growable和Shrinkable特征。虽然它们不能保证这些操作具有良好的性能，但它们会为您提供您想要检查的集合。|244910|entityMap|0|LINK|mutability|MUTABLE|url|http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/library/index.html#scala.collection.generic.Growable|1|http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/library/index.html#scala.collection.generic.Shrinkable^0|0|0|G|9|0|0|J|5|0|0|0|0|0|3|A|4|Z|6|1E|6|0|D|3|1W|4|21|6|2J|6|36|4|0|E|9|0|4|10|0|B|5|0|J|5|15|5|0|8|5|W|5|1K|6|2Y|3|38|5|2W|8|0|C|5|M|5|0|0|0|0|2|2|E|2|T|2|Z|5|15|4|0|0|8|6|N|4|26|6|0|A|5|11|5|0|13|8|1C|A|13|8|0|1C|A|1|0^^$0|@$1|2|3|4|5|6|7|23|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|24|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|25|8|@$G|26|H|27|I|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|28|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|29|8|@$G|2A|H|2B|I|J]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|2C|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|2D|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|2E|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|2F|8|@$G|2G|H|2H|I|J]|$G|2I|H|2J|I|J]|$G|2K|H|2L|I|J]|$G|2M|H|2N|I|J]]|9|@]|A|$]]|$1|V|3|W|5|6|7|2O|8|@$G|2P|H|2Q|I|J]|$G|2R|H|2S|I|J]|$G|2T|H|2U|I|J]|$G|2V|H|2W|I|J]|$G|2X|H|2Y|I|J]]|9|@]|A|$]]|$1|X|3|Y|5|6|7|2Z|8|@$G|30|H|31|I|J]]|9|@]|A|$]]|$1|Z|3|10|5|6|7|32|8|@$G|33|H|34|I|J]]|9|@]|A|$]]|$1|11|3|12|5|6|7|35|8|@$G|36|H|37|I|J]]|9|@]|A|$]]|$1|13|3|14|5|6|7|38|8|@$G|39|H|3A|I|J]|$G|3B|H|3C|I|J]]|9|@]|A|$]]|$1|15|3|16|5|6|7|3D|8|@$G|3E|H|3F|I|J]|$G|3G|H|3H|I|J]|$G|3I|H|3J|I|J]|$G|3K|H|3L|I|J]|$G|3M|H|3N|I|J]|$G|3O|H|3P|I|17]]|9|@]|A|$]]|$1|18|3|19|5|6|7|3Q|8|@$G|3R|H|3S|I|J]|$G|3T|H|3U|I|J]]|9|@]|A|$]]|$1|1A|3|1B|5|6|7|3V|8|@]|9|@]|A|$]]|$1|1C|3|1D|5|6|7|3W|8|@]|9|@]|A|$]]|$1|1E|3|1F|5|1G|7|3X|8|@]|9|@]|A|$1H|1I]]|$1|1J|3|1K|5|6|7|3Y|8|@$G|3Z|H|40|I|J]|$G|41|H|42|I|J]|$G|43|H|44|I|J]|$G|45|H|46|I|J]|$G|47|H|48|I|J]]|9|@]|A|$]]|$1|1L|3|1M|5|6|7|49|8|@]|9|@]|A|$]]|$1|1N|3|1O|5|6|7|4A|8|@$G|4B|H|4C|I|J]|$G|4D|H|4E|I|J]|$G|4F|H|4G|I|J]]|9|@]|A|$]]|$1|1P|3|1Q|5|6|7|4H|8|@$G|4I|H|4J|I|J]|$G|4K|H|4L|I|J]]|9|@]|A|$]]|$1|1R|3|1S|5|6|7|4M|8|@$G|4N|H|4O|I|J]|$G|4P|H|4Q|I|J]]|9|@$G|4R|H|4S|1|4T]|$G|4U|H|4V|1|4W]]|A|$]]|$1|1T|3|-4|5|6|7|4X|8|@]|9|@]|A|$]]]|1U|$1V|$5|1W|1X|1Y|A|$1Z|20]]|21|$5|1W|1X|1Y|A|$1Z|22]]]]

I can think of 3 more specific questions to address yours:

<ul>
<li>What is Scala's default collection?</li>
<li>What Scala collection has characteristics similar to <code>ArrayList</code>?</li>
<li>What's a good replacement for <code>Array</code> in Scala?</li>
</ul>

So here are the answers for these:

<h2>What is Scala's default collection?</h2>

Scala's equivalent of Java's <code>List</code> interface is the <code>Seq</code>. A more general interface exists as well, which is the <code>GenSeq</code> -- the main difference being that a <code>GenSeq</code> may have operations processed serially or in parallel, depending on the implementation.

Because Scala allows programmers to use <code>Seq</code> as a factory, they don't often bother with defining a particular implementation unless they care about it. When they do, they'll usually pick either Scala's <code>List</code> or <code>Vector</code>. They are both immutable, and <code>Vector</code> has good indexed access performance. On the other hand, <code>List</code> does very well the operations it does well.

<h2>What Scala collection has characteristics similar to <code>ArrayList</code>?</h2>

That would be <code>scala.collection.mutable.ArrayBuffer</code>.

<h2>What's a good replacement for <code>Array</code> in Scala?</h2>

Well, the good news is, you can just use <code>Array</code> in Scala! In Java, <code>Array</code> is often avoided because of its general incompatibility with generics. It is a co-variant collection, whereas generics is invariant, it is mutable -- which makes its co-variance a danger, it accepts primitives where generics don't, and it has a pretty limited set of methods.

In Scala, <code>Array</code> -- which is still the same <code>Array</code> as in Java -- is invariant, which makes most problems go away. Scala accepts <code>AnyVal</code> (the equivalent of primitives) as types for its "generics", even though it will do auto-boxing. And through the "enrich my library" pattern, ALL of <code>Seq</code> methods are available to <code>Array</code>.

So, if you want a more powerful <code>Array</code>, just use an <code>Array</code>.

<h2>What about a collection that shrinks and grows?</h2>

The default methods available to all collections all produce new collections. For example, if I do this:

<pre><code>val ys = xs filter (x =&gt; x % 2 == 0)
</code></pre>

Then <code>ys</code> will be a new collection, while <code>xs</code> will still be the same as before this command. This is true no matter what <code>xs</code> was: <code>Array</code>, <code>List</code>, etc.

Naturally, this has a cost -- after all, you are producing a new collection. Scala's immutable collections are much better at handling this cost because they are persistent, but it depends on what operation is executed.

No collection can do much about <code>filter</code>, but a <code>List</code> has excellent performance on generating a new collection by prepending an element or removing the head -- the basic operations of a stack, as a matter of fact. <code>Vector</code> has good performance on a bunch of operations, but it only pays if the collection isn't small. For collections of, say, up to a hundred elements, the overall cost might exceed the gains.

So you can actually add or remove elements to an <code>Array</code>, and Scala will produce a new <code>Array</code> for you, but you'll pay the cost of a full copy when you do that.

Scala mutable collections add a few other methods. In particular, the collections that can increase or decrease size -- without producing a new collection -- implement the <a href="http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/library/index.html#scala.collection.generic.Growable" rel="noreferrer"><code>Growable</code></a> and <a href="http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/library/index.html#scala.collection.generic.Shrinkable" rel="noreferrer"><code>Shrinkable</code></a> traits. They don't guarantee good performance on these operations, though, but they'll point you to the collections you want to check out.

I am doing a project in Scala, but am fairly new to the language and have a Java background. I see that Scala doesn't have ArrayList, so I am wondering what Scala's equivalent of Java's ArrayList is called, and if there are any important differences between the Java and Scala versions.

EDIT: I'm not looking for a specific behavior so much as an internal representation (data stored in an array, but the whole array isn't visible, only the part you use).

Scala equivalent of java.util.ArrayList

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Java

我正在用Scala做一个项目，但我对这门语言相当陌生，而且有Java背景。我发现Scala没有ArrayList，所以我想知道Scala与Java的ArrayList的等价物是什么，以及在Java和Scala版本之间是否有什么重要的区别。EDIT:我寻找的不是一个特定的行为，而是一个内部表示(数据存储在一个数组中，但整...

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