为什么在使用反射调用方法时，我得到“对象不是声明类的实例”？

reflection java illegalargumentexception

2022-09-01 04:54:55

public class Shared {

    public static void main(String arg[]) throws SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException {
        Shared s1 = new Shared();

        Object obj[] = new Object[2];
        obj[0] = "object1";
        obj[1] = "object2";
        s1.testParam(null, obj);

        Class param[] = new Class[2];
        param[0] = String.class;
        param[1] = Object[].class; //// how to define the second parameter as array
        Method testParamMethod = s1.getClass().getDeclaredMethod("testParam", param);
        testParamMethod.invoke("", obj); ///// here getting error
    }

    public void testParam(String query,Object ... params){
        System.out.println("in the testparam method");
    }

}

下面是输出：

in the testparam method
Exception in thread "main" java.lang.IllegalArgumentException: object is not an instance of declaring class
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at pkg.Shared.main(Shared.java:20)

答案 1

通过反射调用方法时，需要将要调用该方法的对象作为第一个参数传递给。Method#invoke

// equivalent to s1.testParam("", obj)
testParamMethod.invoke(s1, "", obj);

答案 2

 testParamMethod.invoke("", obj); ///// here getting error

要调用的第一个参数必须是要在其上调用它的对象：

 testParamMethod.invoke(s1, "", obj);