java.lang.ClassCastException
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/3511169/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
java.lang.ClassCastException
提问by selvam
Normally whats the reason to get java.lang.ClassCastException ..? I get the following error in my application
通常是什么原因得到 java.lang.ClassCastException ..？我的应用程序中出现以下错误
java.lang.ClassCastException: [Lcom.rsa.authagent.authapi.realmstat.AUTHw
采纳答案by Lauren?iu Dasc?lu
According to the documentation:
根据文档：
Thrown to indicate that the code has attempted to cast an Objectto a subclass
of which it is not an instance. For example, the following code generates a ClassCastException:
抛出以指示代码已尝试将 anObject强制转换为它不是其实例的子类。例如，以下代码生成一个ClassCastException：
Object x = new Integer(0);
System.out.println((String)x);
回答by Jon Skeet
It's because you're casting to the wrong thing - you're trying to convert to a particular type, and the object that your express refers to is incompatible with that type. For example:
这是因为您正在转换为错误的东西 - 您正在尝试转换为特定类型，并且您的 express 引用的对象与该类型不兼容。例如：
Object x = "this is a string";
InputStream y = (InputStream) x; // This will throw ClassCastException
If you could provide a code sample, that would really help...
如果你能提供一个代码示例，那真的很有帮助......
回答by PaulJWilliams
ClassA a = <something>;
ClassB b = (ClassB) a;
The 2nd line will fail if ClassA is not a subclass of ClassB, and will throw a ClassCastException.
如果 ClassA 不是 ClassB 的子类，第二行将失败，并抛出 ClassCastException。
回答by Stephen C
@Lauren?iu Dasc?lu's answer explains how / why you get a ClassCastException.
@Lauren?iu Dasc?lu 的回答解释了您如何/为什么会收到 ClassCastException。
Your exception message looks rather suspicious to me, but it might help you to know that "[Lcom.rsa.authagent.authapi.realmstat.AUTHw" means that the actual type of the object that you were trying to cast was com.rsa.authagent.authapi.realmstat.AUTHw[]; i.e. it was an array object.
您的异常消息对我来说看起来很可疑，但它可能会帮助您了解“[Lcom.rsa.authagent.authapi.realmstat.AUTHw”意味着您尝试投射的对象的实际类型是com.rsa.authagent.authapi.realmstat.AUTHw[]；即它是一个数组对象。
Normally, the next steps to solving a problem like this are:
通常，解决此类问题的下一步是：
- examining the stacktrace to figure out which line of which class threw the exception,
- examining the corresponding source code, to see what the expected type, and
- tracing back to see where the object with the "wrong" type came from.
- 检查堆栈跟踪以找出哪个类的哪一行引发了异常，
- 检查相应的源代码，看看预期的类型，以及
- 回溯以查看具有“错误”类型的对象的来源。
回答by mR_fr0g
A ClassCastExceptionocurrs when you try to cast an instance of an Object to a type that it is not. Casting only works when the casted object follows an "is a" relationship to the type you are trying to cast to. For Example
一个ClassCastException当您尝试转换为一个类型的对象的实例，它不是ocurrs。仅当被转换的对象与您尝试转换为的类型遵循“是”关系时，转换才有效。例如
Apple myApple = new Apple();
Fruit myFruit = (Fruit)myApple;
This works because an apple 'is a' fruit. However if we reverse this.
这是有效的，因为苹果“是”水果。但是，如果我们扭转这一点。
Fruit myFruit = new Fruit();
Apple myApple = (Apple)myFruit;
This will throw a ClasCastException because a Fruit is not (always) an Apple.
这将抛出 ClasCastException 因为 Fruit 不是（总是）Apple。
It is good practice to guard any explicit casts with an instanceofcheck first:
最好instanceof先通过检查来保护任何显式强制转换：
if (myApple instanceof Fruit) {
Fruit myFruit = (Fruit)myApple;
}
回答by Pushpraj Mehta
To avoid x !instance of Longprob
Add
为了避免x !instance of Long问题添加
<property name="openjpa.Compatibility" value="StrictIdentityValues=false"/>
in your persistence.xml
在你的persistence.xml
