blocks|key|5266387|text|在C#中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5266388|已根据Mike的建议进行修复|offset|length|5266389|ArrayList+list+=+...;
//+List<object>+list+=+...;
foreach+(object+o+in+list)+{
++++if+(o+is+int)+{
++++++++HandleInt((int)o);
++++}
++++else+if+(o+is+string)+{
++++++++HandleString((string)o);
++++}
++++...
}|code-block|syntax|javascript|5266390|在Java中：|5266391|ArrayList<Object>+list+=+...;
for+(Object+o+:+list)+{
++++if+(o+instanceof+Integer))+{
++++++++handleInt((Integer+o).intValue());
++++}
++++else+if+(o+instanceof+String))+{
++++++++handleString((String)o);
++++}
++++...
}|5266392|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/14359/mike-brown^0|0|3|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@$D|Y|E|Z|1|10]]|A|$]]|$1|F|3|G|5|H|7|11|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|13|8|@]|9|@]|A|$I|J]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

In C#: Fixed with recommendation from <a href="https://stackoverflow.com/users/14359/mike-brown">Mike</a>

<pre><code>ArrayList list = ...;
// List&lt;object&gt; list = ...;
foreach (object o in list) {
 if (o is int) {
 HandleInt((int)o);
 }
 else if (o is string) {
 HandleString((string)o);
 }
 ...
}
</code></pre>

In Java:

<pre><code>ArrayList&lt;Object&gt; list = ...;
for (Object o : list) {
 if (o instanceof Integer)) {
 handleInt((Integer o).intValue());
 }
 else if (o instanceof String)) {
 handleString((String)o);
 }
 ...
}
</code></pre>

blocks|key|5266443|text|您可以使用getClass()方法，也可以使用instanceof。例如|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5266444|for+(Object+obj+:+list)+{
++if+(obj+instanceof+String)+{
+++...
++}
}|code-block|syntax|javascript|5266445|或|5266446|for+(Object+obj+:+list)+{
+if+(obj.getClass().equals(String.class))+{
+++...
+}
}|5266447|请注意，instanceof将匹配子类。例如，of+C是A的子类，则以下条件将为真：|5266448|C+c+=+new+C();
assert+c+instanceof+A;|5266449|但是，以下内容将是错误的：|5266450|C+c+=+new+C();
assert+!c.getClass().equals(A.class)|5266451|entityMap^0|5|A|0|0|0|0|Q|1|S|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1A|8|@]|D|@]|E|$]]|$1|U|3|V|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|W|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|X|$]]

You can use the <code>getClass()</code> method, or you can use instanceof. For example

<pre><code>for (Object obj : list) {
 if (obj instanceof String) {
 ...
 }
}
</code></pre>

or

<pre><code>for (Object obj : list) {
 if (obj.getClass().equals(String.class)) {
 ...
 }
}
</code></pre>

Note that instanceof will match subclasses. For instance, of <code>C</code> is a subclass of <code>A</code>, then the following will be true:

<pre><code>C c = new C();
assert c instanceof A;
</code></pre>

However, the following will be false:

<pre><code>C c = new C();
assert !c.getClass().equals(A.class)
</code></pre>

blocks|key|3855189|text|for+(Object+object+:+list)+{
++++System.out.println(object.getClass().getName());
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3855190|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>for (Object object : list) {
 System.out.println(object.getClass().getName());
}
</code></pre>

blocks|key|761352|text|你几乎永远不会想要使用像这样的东西：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|761353|Object+o+=+...
if+(o.getClass().equals(Foo.class))+{
++++...
}|code-block|syntax|javascript|761354|因为您没有考虑到可能的子类。你真的想要使用Class#isAssignableFrom：|761355|Object+o+=+...
if+(Foo.class.isAssignableFrom(o))+{
++++...
}|761356|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You almost never want you use something like:

<pre><code>Object o = ...
if (o.getClass().equals(Foo.class)) {
 ...
}
</code></pre>

because you aren't accounting for possible subclasses. You really want to use Class#isAssignableFrom:

<pre><code>Object o = ...
if (Foo.class.isAssignableFrom(o)) {
 ...
}
</code></pre>

blocks|key|5266730|text|在Java中，只需使用instanceof操作符。这也会照顾到子类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5266731|ArrayList<Object>+listOfObjects+=+new+ArrayList<Object>();
for(Object+obj:+listOfObjects){
+++if(obj+instanceof+String){
+++}else+if(obj+instanceof+Integer){
+++}etc...
}|code-block|syntax|javascript|5266732|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|$]]

In Java just use the instanceof operator. This will also take care of subclasses.

<pre><code>ArrayList&lt;Object&gt; listOfObjects = new ArrayList&lt;Object&gt;();
for(Object obj: listOfObjects){
 if(obj instanceof String){
 }else if(obj instanceof Integer){
 }etc...
}
</code></pre>

blocks|key|3011170|text|import+java.util.ArrayList;

/**
+*+@author+potter
+*
+*/
public+class+storeAny+{

++++/**
+++++*+@param+args
+++++*/
++++public+static+void+main(String[]+args)+{
++++++++//+TODO+Auto-generated+method+stub

++++++++ArrayList<Object>+anyTy=new+ArrayList<Object>();
++++++++anyTy.add(new+Integer(1));
++++++++anyTy.add(new+String("Jesus"));
++++++++anyTy.add(new+Double(12.88));
++++++++anyTy.add(new+Double(12.89));
++++++++anyTy.add(new+Double(12.84));
++++++++anyTy.add(new+Double(12.82));

++++++++for+(Object+o+:+anyTy)+{
++++++++++++if(o+instanceof+String){
++++++++++++++++System.out.println(o.toString());
++++++++++++}+else+if(o+instanceof+Integer)+{
++++++++++++++++System.out.println(o.toString());+++
++++++++++++}+else+if(o+instanceof+Double)+{
++++++++++++++++System.out.println(o.toString());
++++++++++++}
++++++++}
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3011171|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>import java.util.ArrayList;

/**
 * @author potter
 *
 */
public class storeAny {

 /**
 * @param args
 */
 public static void main(String[] args) {
 // TODO Auto-generated method stub

 ArrayList&lt;Object&gt; anyTy=new ArrayList&lt;Object&gt;();
 anyTy.add(new Integer(1));
 anyTy.add(new String("Jesus"));
 anyTy.add(new Double(12.88));
 anyTy.add(new Double(12.89));
 anyTy.add(new Double(12.84));
 anyTy.add(new Double(12.82));

 for (Object o : anyTy) {
 if(o instanceof String){
 System.out.println(o.toString());
 } else if(o instanceof Integer) {
 System.out.println(o.toString()); 
 } else if(o instanceof Double) {
 System.out.println(o.toString());
 }
 }
 }
}
</code></pre>

blocks|key|5266381|text|只需在循环中的每个Object上调用.getClass()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5266382|不幸的是，Java没有map()。:)|5266383|entityMap^0|9|6|I|B|0|B|5|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

Just call <code>.getClass()</code> on each <code>Object</code> in a loop.

Unfortunately, Java doesn't have <code>map()</code>. :)

blocks|key|3855322|text|如果您不依赖于特定的类，但也要记住列表中可以有空值，那么obj.getClass()就会失败，但是Instanceof总是在null时返回false。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3855323|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Instanceof works if you don't depend on specific classes, but also keep in mind that you can have nulls in the list, so obj.getClass() will fail, but instanceof always returns false on null.

blocks|key|3011245|text|从Java+8开始|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3011246|​|3011247|++++++++mixedArrayList.forEach((o)+->+{
++++++++++++String+type+=+o.getClass().getSimpleName();
++++++++++++switch+(type)+{
++++++++++++++++case+"String":
++++++++++++++++++++//+treat+as+a+String
++++++++++++++++++++break;
++++++++++++++++case+"Integer":
++++++++++++++++++++//+treat+as+an+int
++++++++++++++++++++break;
++++++++++++++++case+"Double":
++++++++++++++++++++//+treat+as+a+double
++++++++++++++++++++break;
++++++++++++++++...
++++++++++++++++default:
++++++++++++++++++++//+whatever
++++++++++++}
++++++++});|code-block|syntax|javascript|3011248|3011249|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

Since Java 8

<pre><code>
 mixedArrayList.forEach((o) -> {
 String type = o.getClass().getSimpleName();
 switch (type) {
 case "String":
 // treat as a String
 break;
 case "Integer":
 // treat as an int
 break;
 case "Double":
 // treat as a double
 break;
 ...
 default:
 // whatever
 }
 });
</pre></code>

blocks|key|5266770|text|您可以使用object.getClass().getSimpleName()而不是object.getClass().getName()，因为它返回一个简单的类名，其中不包括包名。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5266771|例如,|5266772|Object[]+intArray+=+{+1+};+

for+(Object+object+:+intArray)+{+
++++System.out.println(object.getClass().getName());
++++System.out.println(object.getClass().getSimpleName());
}|code-block|syntax|javascript|5266773|给予，|5266774|java.lang.Integer
Integer|5266775|entityMap^0|5|X|15|R|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$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]]|$1|Q|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|R|$]]

instead of using <code>object.getClass().getName()</code> you can use <code>object.getClass().getSimpleName()</code>, because it returns a simple class name without a package name included.

for instance,

<pre><code>Object[] intArray = { 1 }; 

for (Object object : intArray) { 
 System.out.println(object.getClass().getName());
 System.out.println(object.getClass().getSimpleName());
}
</code></pre>

gives,

<pre><code>java.lang.Integer
Integer
</code></pre>

blocks|key|5266583|text|您说“这是一段正在编写的java代码”，我由此推断，您仍有可能以不同的方式设计它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5266584|拥有一个ArrayList就像拥有一堆东西。与其在每次从列表中获取对象时强制instanceof或getClass，为什么不设计系统，让您在从DB检索对象时获得对象的类型，并将其存储到适当类型的对象的集合中？|5266585|或者，您可以使用现有的许多数据访问库中的一个来为您完成此操作。|5266586|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

You say "this is a piece of java code being written", from which I infer that there is still a chance that you could design it a different way. 

Having an ArrayList is like having a collection of stuff. Rather than force the instanceof or getClass every time you take an object from the list, why not design the system so that you get the type of the object when you retrieve it from the DB, and store it into a collection of the appropriate type of object?

Or, you could use one of the many data access libraries that exist to do this for you.

blocks|key|5266704|text|如果您希望数据是某种形式的数字，而您感兴趣的只是将结果转换为数值，那么我建议您：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5266705|for+(Object+o:list)+{
++Double.parseDouble(o.toString);
}|code-block|syntax|javascript|5266706|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 expect the data to be numeric in some form, and all you are interested in doing is converting the result to a numeric value, I would suggest:

<pre><code>for (Object o:list) {
 Double.parseDouble(o.toString);
}
</code></pre>

I have a ArrayList made up of different elements imported from a db, made up of strings, numbers, doubles and ints. Is there a way to use a reflection type technique to find out what each type of data each element holds? 

FYI: The reason that there is so many types of data is that this is a piece of java code being written to be implemented with different DB's.

How do I find out what type each object is in a ArrayList<Object>?

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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我有一个由从数据库导入的不同元素组成的ArrayList，由字符串、数字、双精度和整数组成。有没有办法使用反射类型技术来找出每个元素包含的每种类型的数据？仅供参考:之所以有这么多类型的数据，是因为这是一段要用不同的DB实现的java代码。

问如何找出ArrayList<Object>中每个对象的类型？
EN

回答 12

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问如何找出ArrayList<Object>中每个对象的类型？EN

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问如何找出ArrayList<Object>中每个对象的类型？
EN