Java 泛型在 Eclipse 中编译，但在 javac 中不编译

2022-01-17 00:00:00 compiler-construction java eclipse generics javac

我不得不发现我的项目中有 Java 代码，它在 Eclipse 中编译和运行良好，但在 javac 中引发编译错误.

I had to discover I have Java code in my project, which compiles and runs fine in Eclipse, but throws a compilation error in javac.

一个独立的片段:

import java.util.HashSet;
import java.util.Set;

public class Main {

    public static void main(String[] args) {
    Set<Integer> setOfInts = new HashSet<Integer>();
    Set<Object> setOfObjects = covariantSet(setOfInts);
    }

    public static <S, T extends S> Set<S> covariantSet(Set<T> set) {
    return new HashSet<S>(set);
    }

}

javac 中的编译返回:

Compilation in javac returns:

Main.java:10: incompatible types
found   : java.util.Set<java.lang.Integer>
required: java.util.Set<java.lang.Object>
    Set<Object> setOfObjects = covariantSet(setOfInts);
                                           ^

此错误现在会阻止在 Maven 中构建项目.由于 Eclipse 编译器被构建为更宽容，我现在不得不假设上面的片段的定义和使用静态方法是无效的 Java?

This error now prevents building the project in Maven. As the Eclipse compiler is built to be more tolerant, I now have to assume the definition and usage of snippets as above static method is no valid Java?

推荐答案

好像Sun的1.6 JDK无法推断出正确的类型.以下似乎适用于我的机器:

It seems that Sun's 1.6 JDK can't infer the correct type. The following seems to work on my machine:

Set<Object> setOfObjects = Main.<Object, Integer>covariantSet(setOfInts);

请注意，您必须调用静态方法以类名为前缀

Note that you must invoke the static method prefixed with the class name

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