java javac 错误：具有泛型的不可转换类型？
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javac error: inconvertible types with generics?
提问by Jason S
There are several other SO questions talking about generics compiling OK w/ Eclipse's compiler but not javac (i.e. Java: Generics handled differenlty in Eclipse and javacand Generics compiles and runs in Eclipse, but doesn't compile in javac) -- however this looks like a slightly different one.
还有其他一些做题谈论泛型编译OK W / Eclipse的编译器，但不是javac的（即Java的：泛型处理differenlty在Eclipse和javac和Eclipse中的泛型可以编译和运行，但在javac还不能编译） -但是这看起来就像一个稍微不同的人。
I have an enumclass:
我有一enum堂课：
public class LogEvent {
public enum Type {
// ... values here ...
}
...
}
and I have another class with a method that takes in arbitrary objects of types descended from Enum:
我有另一个类，它的方法接受来自Enum以下类型的任意对象：
@Override public <E extends Enum<E>> void postEvent(
Context context, E code, Object additionalData)
{
if (code instanceof LogEvent.Type)
{
LogEvent.Type scode = (LogEvent.Type)code;
...
This works fine in Eclipse, but when I do a clean built with ant, I am getting a pair of errors, one on the instanceofline, the other on the casting line:
这在 Eclipse 中运行良好，但是当我使用 进行干净的构建时ant，我收到了一对错误，一个instanceof在线上，另一个在铸造线上：
443: inconvertible types
[javac] found : E
[javac] required: mypackage.LogEvent.Type
[javac] if (code instanceof LogEvent.Type)
[javac] ^
445: inconvertible types
[javac] found : E
[javac] required: com.dekaresearch.tools.espdf.LogEvent.Type
[javac] LogEvent.Type scode = (LogEvent.Type)code;
[javac] ^
Why does this happen, and how can I get around this problem so it will compile properly?
为什么会发生这种情况，我该如何解决这个问题，以便正确编译？
回答by Jon Skeet
I don't know why it's happening, but a workaround is easy:
我不知道为什么会这样，但解决方法很简单：
@Override public <E extends Enum<E>> void postEvent(
Context context, E code, Object additionalData)
{
Object tmp = code;
if (tmp instanceof LogEvent.Type)
{
LogEvent.Type scode = (LogEvent.Type)tmp;
...
It's ugly, but it works...
这很丑陋，但它有效......
回答by Sergei Tachenov
Perhaps it is because you've declared E as something that extends Enum<E>. I can't say I understand it completely, but it looks like it limits the set of types to some subset that can't include LogEvent.Type for some reason. Or maybe it's just a bug in the compiler. I'd be happy if someone could explain it more clearly, but here is what you can do:
也许是因为您已将 E 声明为扩展 Enum<E> 的东西。我不能说我完全理解它，但它似乎将类型集限制为某些子集，由于某种原因不能包含 LogEvent.Type。或者它可能只是编译器中的一个错误。如果有人可以更清楚地解释它，我会很高兴，但您可以这样做：
public <E extends Enum<?>> void postEvent(E code)
{
if (code instanceof LogEvent.Type)
{
LogEvent.Type scode = (LogEvent.Type)code;
...
}
...
This works and it is more elegant than just casting to an Object.
这很有效，而且比仅仅投射到对象更优雅。
回答by WW.
I had a similar problem and upgraded from jdk1.6.0_16 to jdk1.6.0_23 and it went away without any code changes.
我有一个类似的问题，从 jdk1.6.0_16 升级到 jdk1.6.0_23，它没有任何代码更改就消失了。
回答by jonescb
In order to use instanceofboth operands have to inherit/implement the same class/interface.
E just can't be cast to LogEvent.Type
为了使用instanceof两个操作数，必须继承/实现相同的类/接口。
E 只是不能转换为 LogEvent.Type
I don't know what your full method looks like, but this should solve your issue by using interfaces and not Generics.
我不知道你的完整方法是什么样的，但这应该通过使用接口而不是泛型来解决你的问题。
public interface EventType { }
public class LogEvent {
public enum Type implements EventType {}
}
public void postEvent(Context context, EventType code, Object additionalData) {
if(code instanceof LogEvent.Type) {
}
}
