为什么在尝试调用main时Class＃getDeclaredMethods0失败？

Question

Why does this code snippet fail with IllegalArgumentException: wrong number of arguments ? Demonstrated code works with ordinary member and static methods, as well as with native declared ones...

   public class Program {
        public static void main(String[] args) throws ReflectiveOperationException {
            //get native getDeclaredMethods method
            Method Class$getDeclaredMethods0 = Class.class.getDeclaredMethod("getDeclaredMethods0", boolean.class);
            Class$getDeclaredMethods0.setAccessible(true);

            //call main
            Method[] methods = (Method[]) Class$getDeclaredMethods0.invoke(Program.class, false);
            Method main = methods[0];
            main.invoke(null, args); // ← Exception in thread "main" java.lang.IllegalArgumentException: wrong number of arguments
            //at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
            //at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
            //at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
            //at java.lang.reflect.Method.invoke(Method.java:606)
            //at Program.main(Program.java:19)
            //at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
            //at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
            //at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
            //at java.lang.reflect.Method.invoke(Method.java:606)
            //at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
        }
    }

Answer 1

It's not clear why you're calling getDeclaredMethods via reflection, but the invocation of main is broken because you're trying to call it as if it had several String parameters - one per value in args . Instead, you want to pass a single argument, of type String[] . You can do that like this:

main.invoke(null, new Object[] { args });