blocks|key|2933311|text|Collection接口具有将Collection转换为数组的方法：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2933312|Object[]+toArray();|code-block|syntax|javascript|2933313|或|2933314|<T>+T[]+toArray(T[]+a);|2933315|您不能仅仅将一个对象从一种类型转换为另一种不相关的类型，然后期望它能够工作。|2933316|打印集合所产生的输出看起来与打印数组时得到的输出类似，这一事实并不意味着什么。|2933317|entityMap^0|0|A|F|A|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|13|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|T|$]]

The <code>Collection</code> interface has methods to convert <code>Collection</code>s to arrays : 

<pre><code>Object[] toArray();
</code></pre>

or 

<pre><code>&lt;T&gt; T[] toArray(T[] a);
</code></pre>

You can't just cast an object one one type to an unrelated type and expect it to work.

The fact that printing the Set produces an output that looks like the output you get when printing an array doesn't mean anything.

blocks|key|2721010|text|final+ArrayList<Integer>+integerList+=+new+ArrayList<>();
final+Integer[]+integerArray+=+new+Integer[integerList.size()];
integerList.toArray(integerArray);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2721011|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>final ArrayList&lt;Integer&gt; integerList = new ArrayList&lt;&gt;();
final Integer[] integerArray = new Integer[integerList.size()];
integerList.toArray(integerArray);
</code></pre>

blocks|key|146676|text|似乎'tbl_analytes‘是一个集合，而不是一个数组。你不能转换它，你必须转换它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|146677|Integer[]+array+=+set.toArray(new+Integer[0]);|code-block|syntax|javascript|146678|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

It seems that 'tbl_analytes' is a Set, not an array. You can not cast it, you have to convert it:

<pre><code>Integer[] array = set.toArray(new Integer[0]);
</code></pre>

blocks|key|2933321|text|您必须使用Collection+interface中定义的toArray(T+a[])-method，将一个空的Integer[]传递给该方法。这个解决方案假设您的列表是List<Integer>类型的。否则，这将失败。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2933322|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html#toArray(T[]))^0|T|E|1K|9|2D|D|5|K|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@$9|U|A|V|1|W]]|E|$]]|$1|F|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

You have to use the <code>toArray(T a[])</code>-method defined in the <a href="https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html#toArray(T[])" rel="nofollow">Collection interface</a>, passing an empty <code>Integer[]</code> to the method. This solution assumes, that your List is of type <code>List&lt;Integer&gt;</code>. Otherwise, this would fail.

blocks|key|2721034|text|Set<Integer>+values+=+(Set<Integer>)+tbl_analytes.getValue();|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2721035|类类型转换异常给出了实际的类型。所以使用这种或更好的泛化(List而不是ArrayList等)。|unstyled|2721036|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>Set&lt;Integer&gt; values = (Set&lt;Integer&gt;) tbl_analytes.getValue();
</code></pre>

The class cast exception gives the actual type. So use that or better a generalisation (List instead of ArrayList etcetera).

blocks|key|144357|text|在Java语言中，数组是基本的。集合不是。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|144358|因为集合是无序的，所以它无法理解如何从内存位置的散列集合构建有序数组。|144359|当您输出一个set时，您正在对该set调用toString方法。|144360|So:|offset|length|style|BOLD|144361|当我调用时使用|144362|blockquote|144363|144364|Integer[]选择=+(Integer[])+tbl_analytes.getValue()；|144365|我得到以下错误：|144366|Caused+by:+java.lang.ClassCastException:+java.util.Collections$UnmodifiableSet+cannot+be+cast+to+[Ljava.lang.Integer;+|CODE|144367|但是当我这样做的时候：|144368|Object+obj+=+tbl_analytes.getValue();
System.out.println(obj);|code-block|syntax|javascript|144369|144370|+I得到以下输出1,7,15|144371|144372|144373|原因是Integer[]在Set<Integer>中是完全不可转换的，但toString的输出源自：|144374|java.util.Collections$UnmodifiableSet扩展了java.util.AbstractCollection|144375|https://docs.oracle.com/javase/10/docs/api/java/util/AbstractCollection.html#toString()|144376|144377|返回此集合的字符串表示形式。字符串表示由一个集合元素列表组成，该列表按照迭代器返回的顺序排列，用方括号("[]")括起来。相邻元素由字符"，“(逗号和空格)分隔。元素被String.valueOf(Object)转换为字符串。|144378|144379|144380|这就是你得到异常的原因。在这个堆栈溢出问题中回答了它的解决方案：|144381|How+to+convert+Set+to+String[]?|144382|entityMap|0|LINK|mutability|MUTABLE|url|1|https://stackoverflow.com/questions/5982447/how-to-convert-setstring-to-string^0|0|0|0|0|3|0|0|0|0|0|0|0|39|0|0|0|0|0|0|0|3|9|D|C|10|8|0|0|11|14|S|0|0|2F|0|0|0|0|0|0|0|0|V|1|0^^$0|@$1|2|3|4|5|6|7|1X|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1Y|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1Z|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|20|8|@$H|21|I|22|J|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|23|8|@]|9|@]|A|$]]|$1|N|3|-4|5|O|7|24|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|25|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|26|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|27|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|28|8|@$H|29|I|2A|J|W]]|9|@]|A|$]]|$1|X|3|Y|5|6|7|2B|8|@]|9|@]|A|$]]|$1|Z|3|10|5|11|7|2C|8|@]|9|@]|A|$12|13]]|$1|14|3|-4|5|6|7|2D|8|@]|9|@]|A|$]]|$1|15|3|16|5|O|7|2E|8|@]|9|@]|A|$]]|$1|17|3|-4|5|6|7|2F|8|@]|9|@]|A|$]]|$1|18|3|-4|5|6|7|2G|8|@]|9|@]|A|$]]|$1|19|3|1A|5|6|7|2H|8|@$H|2I|I|2J|J|W]|$H|2K|I|2L|J|W]|$H|2M|I|2N|J|W]]|9|@]|A|$]]|$1|1B|3|1C|5|6|7|2O|8|@$H|2P|I|2Q|J|K]|$H|2R|I|2S|J|K]]|9|@]|A|$]]|$1|1D|3|1E|5|6|7|2T|8|@]|9|@$H|2U|I|2V|1|2W]]|A|$]]|$1|1F|3|-4|5|6|7|2X|8|@]|9|@]|A|$]]|$1|1G|3|1H|5|O|7|2Y|8|@]|9|@]|A|$]]|$1|1I|3|-4|5|6|7|2Z|8|@]|9|@]|A|$]]|$1|1J|3|-4|5|6|7|30|8|@]|9|@]|A|$]]|$1|1K|3|1L|5|6|7|31|8|@]|9|@]|A|$]]|$1|1M|3|1N|5|6|7|32|8|@]|9|@$H|33|I|34|1|35]]|A|$]]|$1|1O|3|-4|5|6|7|36|8|@]|9|@]|A|$]]]|1P|$1Q|$5|1R|1S|1T|A|$1U|1E]]|1V|$5|1R|1S|1T|A|$1U|1W]]]]

In the java language arrays are primitive. Collections are not.

Since a set is unordered it has no way to understand how to build an ordered array from a hashed set of memory locations.

When you output a set you are calling the toString method on that set.

So:

<blockquote>
 When I call 

<pre><code>Integer[] selects = (Integer[]) tbl_analytes.getValue();
</code></pre>
 
 I get the following error:
 
 <code>
 Caused by: java.lang.ClassCastException: java.util.Collections$UnmodifiableSet cannot be cast to [Ljava.lang.Integer;
 </code>
</blockquote>

But when I do this:

<pre><code>Object obj = tbl_analytes.getValue();
System.out.println(obj);
</code></pre>

<blockquote>
 I get the following output
 [1,7,15]
</blockquote>

The reason is <code>Integer[]</code> is completely uncastable from <code>Set&lt;Integer&gt;</code> but
 the output from <code>toString</code> is derived from:

The java.util.Collections$UnmodifiableSet extends java.util.AbstractCollection

<a href="https://docs.oracle.com/javase/10/docs/api/java/util/AbstractCollection.html#toString()" rel="nofollow noreferrer">https://docs.oracle.com/javase/10/docs/api/java/util/AbstractCollection.html#toString()</a>

<blockquote>
 Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).
</blockquote>

That is the resason you are getting the exception. The solution to it is answered here in this stack overflow question:

<a href="https://stackoverflow.com/questions/5982447/how-to-convert-setstring-to-string">How to convert Set&lt;String&gt; to String[]?</a>

When I run my code I get the following error:

<pre><code>Caused by: java.lang.ClassCastException: java.util.Collections$UnmodifiableSet cannot be cast to [Ljava.lang.Integer;
</code></pre>

The code that causes is:

<pre><code>Integer[] selects = (Integer[]) tbl_analytes.getValue();
</code></pre>

But when I do this:

<pre><code>Object obj = tbl_analytes.getValue();
System.out.println(obj);
</code></pre>

I get the following output:

<blockquote>
 [1,7,15]
</blockquote>

I don't understand why I can't convert this to an <code>Integer[]</code>. Any tips?

Convert java.util.Collections to Integer array

Java

当我运行我的代码时，我得到以下错误：Caused by: java.lang.ClassCastException: java.util.Collections$UnmodifiableSet cannot be cast to [Ljava.lang.Integer;导致的代码是：Integer[] selects = (Integer[]) tbl_analytes.getValue();但是

问将java.util.Collections转换为整数数组
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