我的Method.invoke调用有什么问题？ [英] What is wrong with my Method.invoke call?

问题描述

我刚刚创建了以下简约测试用例：

I just created the following minimalistic testcase:

package testcase;

public class Main
{

    public static void main( String[] args )
        throws Throwable
    {
        if ( args.length == 0 )
            Main.class.getMethod( "main", String[].class ).invoke( null, new String[] { "test" } );
    }

}

它应该只运行，没有输出，也不例外。 main 方法应该使用反射进行自我调用。但是我得到以下异常：

It should just run, with no output and no exception. The main method should be calling itself using reflection. However I get the following exception:

Exception in thread "main" java.lang.IllegalArgumentException: argument type mismatch
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at testcase.Main.main(Main.java:10)

我不知道为什么，为什么...

And I cannot figure out, why...

推荐答案

使用

public static void main(String[] args) throws Throwable {
    if (args.length == 0)
        Main.class.getMethod("main", String[].class)
                  .invoke(null, new Object[] {new String[] { "test" }});
}

问题是调用具有vararg参数，它可以是数组或对象的简单列表，而Java数组是协变的。因此，编译器以 .invoke（null，new String [] { test}）解释与 .invoke（null，new Object [] { test}）。您应该向编译器发出有关此歧义的警告。

The problem is that invoke has vararg parameter which could be either array or plain list of objects and Java arrays are covariant. So .invoke(null, new String[] { "test" }) is interpreted by compiler in the same way as .invoke(null, new Object[] { "test" }). You should have compiler warning about this ambiguity.

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