blocks|key|382493|text|这是不可能的，因为泛型的数据类型在编译时会被擦除。要做到这一点，唯一可能的方法是编写某种类型的包装器，其中包含列表包含的类型：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382494|public+class+GenericList+<T>+extends+ArrayList<T>
{
+++++private+Class<T>+genericType;

+++++public+GenericList(Class<T>+c)
+++++{
++++++++++this.genericType+=+c;
+++++}

+++++public+Class<T>+getGenericType()
+++++{
++++++++++return+genericType;
+++++}
}|code-block|syntax|javascript|382495|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|$]]

That is not possible because the datatype erasure at compile time of generics. Only possible way of doing this is to write some kind of wrapper that holds which type the list holds:

<pre><code>public class GenericList &lt;T&gt; extends ArrayList&lt;T&gt;
{
 private Class&lt;T&gt; genericType;

 public GenericList(Class&lt;T&gt; c)
 {
 this.genericType = c;
 }

 public Class&lt;T&gt; getGenericType()
 {
 return genericType;
 }
}
</code></pre>

blocks|key|382534|text|if(!myList.isEmpty()+&&+myList.get(0)+instanceof+MyType){
++++//+MyType+object
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|382535|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>if(!myList.isEmpty() &amp;&amp; myList.get(0) instanceof MyType){
 // MyType object
}
</code></pre>

blocks|key|598430|text|您可能需要使用反射来检查它们的类型。要获取列表的类型：Get+generic+type+of+java.util.List|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|598431|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/1942644/get-generic-type-of-java-util-list^0|R|Y|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You probably need to use reflection to get the types of them to check.
To get the type of the List:
<a href="https://stackoverflow.com/questions/1942644/get-generic-type-of-java-util-list">Get generic type of java.util.List</a>

blocks|key|382762|text|如果您想要检查object是否为List<T>的实例，则可以使用此选项，该实例不为空：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|382763|if(object+instanceof+List){
++++if(((List)object).size()>0+&&+(((List)object).get(0)+instanceof+MyObject)){
++++++++//+The+object+is+of+List<MyObject>+and+is+not+empty.+Do+something+with+it.
++++}
}|code-block|syntax|javascript|382764|entityMap^0|7|6|G|7|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

This could be used if you want to check that <code>object</code> is instance of <code>List&lt;T&gt;</code>, which is not empty:

<pre><code>if(object instanceof List){
 if(((List)object).size()&gt;0 &amp;&amp; (((List)object).get(0) instanceof MyObject)){
 // The object is of List&lt;MyObject&gt; and is not empty. Do something with it.
 }
}
</code></pre>

blocks|key|598687|text|++++if+(list+instanceof+List+&&+((List)+list).stream()
+++++++++++++++++++++++++++++++++++++++++++++.noneMatch((o+->+!(o+instanceof+MyType))))+{}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|598688|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> if (list instanceof List &amp;&amp; ((List) list).stream()
 .noneMatch((o -&gt; !(o instanceof MyType)))) {}
</code></pre>

blocks|key|382572|text|如果您正在验证List的引用或Object的映射值是否为Collection的实例，只需创建一个required+List的实例并获取其类...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382573|Set<Object>+setOfIntegers+=+new+HashSet(Arrays.asList(2,+4,+5));
assetThat(setOfIntegers).instanceOf(new+ArrayList<Integer>().getClass());

Set<Object>+setOfStrings+=+new+HashSet(Arrays.asList("my",+"name",+"is"));
assetThat(setOfStrings).instanceOf(new+ArrayList<String>().getClass());|code-block|syntax|javascript|382574|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|$]]

If you are verifying if a reference of a List or Map value of Object is an instance of a Collection, just create an instance of required List and get its class...

<pre><code>Set&lt;Object&gt; setOfIntegers = new HashSet(Arrays.asList(2, 4, 5));
assetThat(setOfIntegers).instanceOf(new ArrayList&lt;Integer&gt;().getClass());

Set&lt;Object&gt; setOfStrings = new HashSet(Arrays.asList("my", "name", "is"));
assetThat(setOfStrings).instanceOf(new ArrayList&lt;String&gt;().getClass());
</code></pre>

blocks|key|598552|text|如果这不能用泛型包装(@Martijn的答案)，最好不要强制转换来传递它，以避免多余的列表迭代(检查第一个元素的类型不能保证任何东西)。我们可以在迭代列表的代码中对每个元素进行强制转换。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|598553|Object+attVal+=+jsonMap.get("attName");
List<Object>+ls+=+new+ArrayList<>();
if+(attVal+instanceof+List)+{
++++ls.addAll((List)+attVal);
}+else+{
++++ls.add(attVal);
}

//+far,+far+away+;)
for+(Object+item+:+ls)+{
++++if+(item+instanceof+String)+{
++++++++System.out.println(item);
++++}+else+{
++++++++throw+new+RuntimeException("Wrong+class+("%2Bitem+.getClass()%2B")+of+"%2Bitem+);
++++}
}|code-block|syntax|javascript|598554|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|$]]

If this can't be wrapped with generics (@Martijn's answer) it's better to pass it without casting to avoid redundant list iteration (checking the first element's type guarantees nothing).
We can cast each element in the piece of code where we iterate the list.

<pre><code>Object attVal = jsonMap.get("attName");
List&lt;Object&gt; ls = new ArrayList&lt;&gt;();
if (attVal instanceof List) {
 ls.addAll((List) attVal);
} else {
 ls.add(attVal);
}

// far, far away ;)
for (Object item : ls) {
 if (item instanceof String) {
 System.out.println(item);
 } else {
 throw new RuntimeException("Wrong class ("+item .getClass()+") of "+item );
 }
}
</code></pre>

blocks|key|598604|text|您可以使用伪工厂来包含许多方法，而不是使用instanceof：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|598605|public+class+Message1+implements+YourInterface+{
+++List<YourObject1>+list;
+++Message1(List<YourObject1>+l)+{
+++++++list+=+l;
+++}
}

public+class+Message2+implements+YourInterface+{
+++List<YourObject2>+list;
+++Message2(List<YourObject2>+l)+{
+++++++list+=+l;
+++}
}

public+class+FactoryMessage+{
++++public+static+List<YourInterface>+getMessage(List<YourObject1>+list)+{
++++++++return+(List<YourInterface>)+new+Message1(list);
++++}
++++public+static+List<YourInterface>+getMessage(List<YourObject2>+list)+{
++++++++return+(List<YourInterface>)+new+Message2(list);
++++}
}|code-block|syntax|javascript|598606|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|$]]

You can use a fake factory to include many methods instead of using instanceof:

<pre><code>public class Message1 implements YourInterface {
 List&lt;YourObject1&gt; list;
 Message1(List&lt;YourObject1&gt; l) {
 list = l;
 }
}

public class Message2 implements YourInterface {
 List&lt;YourObject2&gt; list;
 Message2(List&lt;YourObject2&gt; l) {
 list = l;
 }
}

public class FactoryMessage {
 public static List&lt;YourInterface&gt; getMessage(List&lt;YourObject1&gt; list) {
 return (List&lt;YourInterface&gt;) new Message1(list);
 }
 public static List&lt;YourInterface&gt; getMessage(List&lt;YourObject2&gt; list) {
 return (List&lt;YourInterface&gt;) new Message2(list);
 }
}
</code></pre>

How can I get this sort of thing to work? I can check if <code>(obj instanceof List&lt;?&gt;)</code> but not if <code>(obj instanceof List&lt;MyType&gt;)</code>. Is there a way this can be done?

how to instanceof List<MyType>?

我怎样才能让这类东西工作呢？我可以检查是否为(obj instanceof List<?>)，但无法检查是否为(obj instanceof List<MyType>)。有没有办法做到这一点？

问如何实例化List<MyType>？
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