空蚀问题分析类字面null类型安全警示 [英] Eclipse null analysis issues null type safety warning for class literal

问题描述

考虑已启用空分析Eclipse项目的以下部分内容：

Consider the following partial content of an Eclipse project that has null analysis enabled:

的火星的Eclipse版本（4.5.0; 20150621-1200）用于Windows 64位的结果
的Oracle JDK 1.8.0_60 的

package-info.java

@org.eclipse.jdt.annotation.NonNullByDefault
package bar;

Foo.java

package bar;

public class Foo {
    public static void main(String[] args) {
    }
}

class Base<T> {
    private final Class<T> type;

    public Base(Class<T> type) {
        this.type = type;
    }

    public Class<T> getType() {
        return this.type;
    }
}

class Derived extends Base<String> {
    public Derived() {
        super(String.class); // <-- Null type safety warning here
    }
}

空分析产生的调用构造函数超下列警告在派生：

Null type safety (type annotations): The expression of type 'Class<String>' needs unchecked conversion to conform to '@NonNull Class<@NonNull String>'

什么是避免这种警告的正确方法？

What is the correct way to avoid this warning?

推荐答案

您所看到的冲突的类型参数之间...

The conflict you are seeing is between the type arguments ...

• ...所需类型的： @NonNull字符串


• ...所提供的类型：字符串

• ... of the required type: @NonNull String
• ... of the provided type: String

非null类型参数到图片，从延伸基地＆LT;弦乐＆GT; ，它的制度下 @NonNullByDefault 被扩展为扩展基地＆LT; @NonNull串＆GT; 。从这里渗滤一路攀升到超级构造函数，类型参数替换为后呈现其签名（@非空类＆LT; @NonNull串＆GT;）。相比之下，类常量是由编译器视为具有类型 @NonNull类＆LT;弦乐方式＆gt; ，这是不兼容的。

The non-null type argument comes into the picture from extends Base<String>, which under the regime of @NonNullByDefault is expanded to extends Base<@NonNull String>. From here it percolates all the way up to the super constructor, to render its signature after type argument substitution as (@NonNull Class<@NonNull String>). By contrast, the class literal is seen by the compiler as having type @NonNull Class<String>, which is not compatible.

真正的解决方案会通过的Bug 477719 ，请参阅尤其是在评论3 F的讨论。

The real solution will come via Bug 477719, see in particular the discussion in comment 3 f.

有关暂且（与Eclipse火星），你可能不得不减少 @NonNullByDefault 的作用，使 @NonNull类＆LT;弦乐＆GT; 将被接受。这可以通过一个更具体的@NNBD宣言类派生的顶部实现像这样

For the time being (with Eclipse Mars) you may have to reduce the effect of @NonNullByDefault so that @NonNull Class<String> will be accepted. This can be achieved by a more specific @NNBD declaration on top of class Derived like this

import static org.eclipse.jdt.annotation.DefaultLocation.*;
...
@NonNullByDefault({PARAMETER, RETURN_TYPE, FIELD, TYPE_BOUND})
class Derived extends Base<String> {
...

在这里，我们正在利用事实上，@NNBD可以进行微调就其所适用的位置。在此声明的差异参数少 @NonNullByDefault 在于省略位置 TYPE_ARGUMENT ，这意味着字符串在扩展基地＆LT;串GT; 将不再受到影响像上面提到。 ERGO超级构造函数现在都会有这样的签名：（@非空类＆LT;串GT;）和所有编译没有警告

Here we are leveraging the fact, the @NNBD can be fine tuned regarding the locations to which it applies. In this declaration the difference to an argument-less @NonNullByDefault lies in omitting the location TYPE_ARGUMENT, which means that String in extends Base<String> will no longer be affected like mentioned above. Ergo the super constructor will now have this signature: (@NonNull Class<String>) and all compiles without warnings.

通过将调整@NNBD优良的类导出此变通办法的范围保持一个尽可能小。

By putting the fine tuned @NNBD on the class Derived the scope of this workaround is kept a small as possible.

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