什么是未经检查的投放，我如何检查？ [英] What is unchecked cast and how do I check it?

问题描述

我想我得到了不受限制的投射意味着（从一个到另一个不同类型的投射），但是检查投射是什么意思？如何检查转换，以便我可以避免在Eclipse中的警告？
感谢，

I think I get what unchecked cast means (casting from one to another of a different type), but what does it mean to "Check" the cast? How can I check the cast so that I can avoid this warning in Eclipse? Thanks,

推荐答案

未经检查的转换意味着你（隐式或显式）从一个泛型类型转换为一个非限定类型或其他方式。例如。此行

Unchecked cast means that you are (implicitly or explicitly) casting from a generic type to a nonqualified type or the other way around. E.g. this line

Set<String> set = new HashSet();

会产生此类警告。

通常有这样的警告的一个很好的理由，所以你应该尝试改善你的代码，而不是抑制警告。引用Effective Java，第2版：

Usually there is a good reason for such warnings, so you should try to improve your code instead of suppressing the warning. Quote from Effective Java, 2nd Edition:

取消每个未经检查的警告。如果
消除所有警告，你放心你的代码是类型安全的，这是一个非常
的好东西。这意味着在运行时你不会得到 ClassCastException ，它
增加你的信心，你的程序是按照你的意图。

Eliminate every unchecked warning that you can. If you eliminate all warnings, you are assured that your code is typesafe, which is a very good thing. It means that you won’t get a ClassCastException at runtime, and it increases your confidence that your program is behaving as you intended.

如果你不能消除警告，并且你可以证明
引发的代码是类型安全的，那么（然后）禁止警告
@SuppressWarnings（unchecked）注释。如果你禁止警告
没有先证明代码是类型安全的，你只给自己一个
假的安全感。代码可以编译而不发出任何警告，但
它仍然可以在运行时抛出 ClassCastException 。然而，如果你忽略
未检查的警告，你知道是安全的（而不是抑制他们），你
将不会注意到一个新的警告作物，这代表一个真正的问题。

If you can’t eliminate a warning, and you can prove that the code that provoked the warning is typesafe, then (and only then) suppress the warning with an @SuppressWarnings("unchecked") annotation. If you suppress warnings without first proving that the code is typesafe, you are only giving yourself a false sense of security. The code may compile without emitting any warnings, but it can still throw a ClassCastException at runtime. If, however, you ignore unchecked warnings that you know to be safe (instead of suppressing them), you won’t notice when a new warning crops up that represents a real problem. The new warning will get lost amidst all the false alarms that you didn’t silence.

当然，这是一个错误的警告。并不总是很容易消除警告与上面的代码。没有看到你的代码，没有办法告诉如何使它安全，虽然。

Of course, it is not always as easy to eliminate warnings as with the code above. Without seeing your code, there is no way to tell how to make it safe though.

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