blocks|key|1916813|text|您可以使用Arrays.asList()创建固定大小的List。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1916814|示例：|1916815|大小为3的List，使用空值初始化：|1916816|List<ArrayList<Object>>+models+=+Arrays.asList+(null,null,null);|code-block|syntax|javascript|1916817|大小为3的List，用非空值初始化：|1916818|List<ArrayList<Object>>+models+=+Arrays.asList+(new+ArrayList<Object>+(),new+ArrayList<Object>+(),new+ArrayList<Object>+());|1916819|大小为10的List，使用空值初始化：|1916820|List<ArrayList<Object>>+models+=+Arrays.asList+((ArrayList<Object>[])new+ArrayList[10]);|1916821|注意，固定大小的列表不支持add操作。您将不得不使用models.set(index,new+ArrayList<Object>())代替。|1916822|编辑：|1916823|下面是使用List+s初始化List的另一种方法：|1916824|List<ArrayList<Object>>+models+=+Arrays.asList+(Stream.generate+(ArrayList::new).limit+(10).toArray+(ArrayList[]::new));|1916825|entityMap^0|5|F|R|4|0|0|5|4|0|0|5|4|0|0|6|4|0|0|D|3|Q|15|0|0|5|4|E|4|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1B|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1F|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1J|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1K|8|@$9|1L|A|1M|B|C]]|D|@]|E|$]]|$1|U|3|V|5|L|7|1N|8|@]|D|@]|E|$M|N]]|$1|W|3|X|5|6|7|1O|8|@$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]]|D|@]|E|$]]|$1|Y|3|Z|5|6|7|1T|8|@]|D|@]|E|$]]|$1|10|3|11|5|6|7|1U|8|@$9|1V|A|1W|B|C]|$9|1X|A|1Y|B|C]]|D|@]|E|$]]|$1|12|3|13|5|L|7|1Z|8|@]|D|@]|E|$M|N]]|$1|14|3|-4|5|6|7|20|8|@]|D|@]|E|$]]]|15|$]]

You can use <code>Arrays.asList()</code> to created fixed sized <code>List</code>s.

Examples:

A <code>List</code> of size 3, initialized with null values:

<pre><code>List&lt;ArrayList&lt;Object&gt;&gt; models = Arrays.asList (null,null,null);
</code></pre>

A <code>List</code> of size 3, initialized with non-null values:

<pre><code>List&lt;ArrayList&lt;Object&gt;&gt; models = Arrays.asList (new ArrayList&lt;Object&gt; (),new ArrayList&lt;Object&gt; (),new ArrayList&lt;Object&gt; ());
</code></pre>

A <code>List</code> of size 10, initialized with null values:

<pre><code>List&lt;ArrayList&lt;Object&gt;&gt; models = Arrays.asList ((ArrayList&lt;Object&gt;[])new ArrayList[10]);
</code></pre>

Note that <code>add</code> operation is not supported for fixed sized lists. You'll have to use <code>models.set(index,new ArrayList&lt;Object&gt;())</code> instead.

EDIT:

Here's another way to initialize the <code>List</code> using <code>Stream</code>s:

<pre><code>List&lt;ArrayList&lt;Object&gt;&gt; models = Arrays.asList (Stream.generate (ArrayList::new).limit (10).toArray (ArrayList[]::new));
</code></pre>

blocks|key|3953173|text|java中没有Array类，但是有一个普通的旧数组声明：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3953174|ArrayList<Object>+[]+array...|code-block|syntax|javascript|3953175|问题是您无法像这样实例化它，因为数组不能是泛型的。|3953176|你真的在寻找Arrays.asList或者更好的某种ImmutableList。|3953177|entityMap^0|7|5|0|0|0|6|D|Q|D|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|P|$]]

There isn't an <code>Array</code> class in java, but there is the plain old array declaration:

<pre><code>ArrayList&lt;Object&gt; [] array...
</code></pre>

Problem is that you will not be able to instantiate it like this, since arrays can not be generic.

You are really looking for either <code>Arrays.asList</code> or much better <code>ImmutableList</code> of some kind.

blocks|key|501190|text|一种更详细但兼容泛型的方法是扩展AbstractList。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|501191|您需要重写的方法在Javadoc中描述：|501192|要实现不可修改的列表，程序员只需扩展该类并为get(int)和size()方法提供实现。
要实现可修改的列表，程序员必须另外重写set(int,+E)方法(否则会抛出UnsupportedOperationException)。|blockquote|501193|因此，实现这三种方法，委托给ArrayList|501194|class+FixedSizedList<T>+extends+AbstractList<T>+{
++private+final+List<T>+delegate;

++FixedSizedList(int+size)+{
++++delegate+=+new+ArrayList<>(Collections.nCopies(size,+null));
++}

++public+T+get(int+i)+{+return+delegate.get(i);+}
++public+int+size()+{+return+delegate.size();+}
++public+T+set(int+i,+T+e)+{+return+delegate.set(i,+e);+}
}|code-block|syntax|javascript|501195|或者，在这种情况下，只需使用数组：|501196|class+FixedSizedList<T>+extends+AbstractList<T>+{
++private+final+Object[]+array;

++FixedSizedList(int+size)+{
++++array+=+new+Object[size];
++}

++public+T+get(int+i)+{+return+(T)+array[i];+}
++public+int+size()+{+return+array.length;+}
++public+T+set(int+i,+T+e)+{
++++T+old+=+(T)+array[i];
++++array[i]+=+e;
++++return+old;
++}
}|501197|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/8/docs/api/java/util/AbstractList.html^0|G|C|G|C|0|0|0|M|8|V|6|1S|B|2B|T|0|E|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@$9|16|A|17|1|18]]|E|$]]|$1|F|3|G|5|6|7|19|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1A|8|@$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|K|3|L|5|6|7|1J|8|@$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|M|3|N|5|O|7|1M|8|@]|D|@]|E|$P|Q]]|$1|R|3|S|5|6|7|1N|8|@]|D|@]|E|$]]|$1|T|3|U|5|O|7|1O|8|@]|D|@]|E|$P|Q]]|$1|V|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]]|W|$X|$5|Y|Z|10|E|$11|12]]]]

A slightly more verbose - but generic-compatible way - of doing it is to extend <a href="https://docs.oracle.com/javase/8/docs/api/java/util/AbstractList.html" rel="nofollow noreferrer"><code>AbstractList</code></a>.

The methods you need to override are described in the Javadoc:

<blockquote>
 To implement an unmodifiable list, the programmer needs only to extend this class and provide implementations for the <code>get(int)</code> and <code>size()</code>methods.
 
 To implement a modifiable list, the programmer must additionally override the <code>set(int, E)</code> method (which otherwise throws an <code>UnsupportedOperationException</code>).
</blockquote>

So, implement these three methods, delegating to an <code>ArrayList</code>:

<pre><code>class FixedSizedList&lt;T&gt; extends AbstractList&lt;T&gt; {
 private final List&lt;T&gt; delegate;

 FixedSizedList(int size) {
 delegate = new ArrayList&lt;&gt;(Collections.nCopies(size, null));
 }

 public T get(int i) { return delegate.get(i); }
 public int size() { return delegate.size(); }
 public T set(int i, T e) { return delegate.set(i, e); }
}
</code></pre>

Or, for that matter, just use an array:

<pre><code>class FixedSizedList&lt;T&gt; extends AbstractList&lt;T&gt; {
 private final Object[] array;

 FixedSizedList(int size) {
 array = new Object[size];
 }

 public T get(int i) { return (T) array[i]; }
 public int size() { return array.length; }
 public T set(int i, T e) {
 T old = (T) array[i];
 array[i] = e;
 return old;
 }
}
</code></pre>

I have this:

<pre><code>private ArrayList&lt;ArrayList&lt;Object&gt;&gt; models;
</code></pre>

and in the constructor I have:

<pre><code>models = new ArrayList&lt;ArrayList&lt;Object&gt;&gt;();
</code></pre>

Later, I do things like:

<pre><code>models.add(new ArrayList&lt;Object&gt;());
</code></pre>

as well as other operations. 

I want to make the external ArrayList to something with a fixed size (Array, List) and I am really lost to how I am going to write the declaration, initialization, addition, etc. because of the nested objects. Can someone save me time by answering this for me?

From ArrayList<ArrayList<Object>> to fixed size array/list

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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我有这个：private ArrayList<ArrayList<Object>> models;在构造函数中，我有：models = new ArrayList<ArrayList<Object>>();后来，我做了这样的事情：models.add(new ArrayList<Object>());以及其他行动。我想...

问从ArrayList<ArrayList<Object>>到固定大小数组/列表
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