Java中未经检查的转换警告 [英] Unchecked cast warning in Java

问题描述

Eclipse表示：类型安全性：当我这样做时，未经检查就从Object转换为ObjectArrayList ：

Eclipse says: Type safety: Unchecked cast from Object to ObjectArrayList<Car> when I do:

final ObjectArrayList<Car> icars = (ObjectArrayList<Car>) cars[i];

其中汽车的定义为：

final Object[] cars = new Object[1000];
for (int i = 0; i < 1000; i++) {
    cars[i] = new ObjectArrayList<Car>();
}

Eclipse建议添加 @SuppressWarnings（ unchecked ）到 icars 对象。但是我读过某处Java不推荐使用注释的地方，所以我应该保留它不变吗？

Eclipse suggests to add @SuppressWarnings("unchecked") to icars object. But I've read somewhere that annotations are deprecated in Java, so should I leave it as it is?

推荐答案

警告是只是，警告您，不能保证正在投射的 cars 数组中的对象是 ObjectArrayList< Car> 。

The warning is just, well, warning you that the objects in the cars array that are being casted aren't guaranteed to be an ObjectArrayList<Car>.

事实证明Java不允许使用泛型类型声明数组，除非它们是无界的（请参见 Java 1.6：创建列表数组，或此错误报告 6229728：允许创建通用数组的特殊情况）。但是如果可以这样声明数组，则不会收到警告：

It turns out Java doesn't allow array declaration with generic types unless they're unbounded (see Java 1.6: Creating an array of List, or this bug report 6229728 : Allow special cases of generic array creation). But if you could declare the array like this, you wouldn't be getting the warning:

final ObjectArrayList<Car>[] cars=new ObjectArrayList<Car>[1000]; // not allowed

如果您确实想避免未经检查的类型，则应使用强类型集合数组（例如， List< ObjectArrayList< Car>> ）。

If you really want to avoid an unchecked cast you should use a strongly typed collection instead of an array (for instance, a List<ObjectArrayList<Car>>).

= http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/SuppressWarnings.html rel = nofollow noreferrer> @SuppressWarnings（ unchecked） 注释只会告诉编译器不要显示警告。除非警告确实使您烦恼，否则我不建议您使用它。现实情况是，您将进行未经检查的强制转换（如果您确定数组中元素的类型，这不是问题）。

The @SuppressWarnings("unchecked") annotation will just tell the compiler not to show the warning. I wouldn't advice using it unless the warning really annoys you. Reality is you'll be doing an unchecked cast (not a problem if you're certain about the type of the elements in the array).

Java中不建议使用注解。实际上，似乎它们将通过Java 8变得更加强大（似乎它们将支持 JSR 308：关于Java类型的注释）。也许您读到 @deprecated 是注释。

As a side note, annotations aren't in any way deprecated in Java. Actually, it seems they'll become more powerful with Java 8 (it seems they'll support JSR 308: Annotations on Java Types). Maybe you read that @Deprecated is an annotation instead.

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