Java：编译时Object的隐式转换不起作用,但可以使用反射

import java.lang.reflect.Array;
import java.lang.reflect.Method;

public class Test {

  public static void test_function(int[] values) {
    System.out.println("Class of values : " + values.getClass());
    System.out.println(values[0]);
  }

  public static void main(String[] args) {

    Object a = Array.newInstance(int.class,3);
    Array.set(a,5);

    Class a_class         = a.getClass();
    Class int_array_class = int[].class;

    System.out.println("Class of int[]  : " + int[].class); 
    System.out.println("Class of a      : " + a.getClass());
    System.out.println("int_array_class : " + int_array_class);
    System.out.println("a_class         : " + a_class);

    // These instructions will provoke a compile-time error
    // test_function(a);
    // test_function(a_class.cast(a));
    // test_function(int_array_class.cast(a));

    // The following call won't cause any problem
    test_function((int[]) a);

    Method testf = null;
    try { 
      testf = Test.class.getMethod("test_function",int[].class);
      testf.invoke(null,a); // Does not provoke exception at run-time either
      testf.invoke(null,a_class.cast(a));
      testf.invoke(null,int_array_class.cast(a));
    }
    catch(Exception e) { 
      e.printStackTrace();
    }

  }

}

我注意到显式地将Object传递给方法不起作用.如果取消注释,三条注释说明将引发以下错误：

Test.java:25: error: method test_function in class Test cannot be applied to given types;
    test_function(a);
    ^
  required: int[]
  found: Object
  reason: actual argument Object cannot be converted to int[] by method invocation conversion
Test.java:26: error: method test_function in class Test cannot be applied to given types;
    test_function(a_class.cast(a));
    ^
  required: int[]
  found: Object
  reason: actual argument Object cannot be converted to int[] by method invocation conversion
Test.java:27: error: method test_function in class Test cannot be applied to given types;
    test_function(int_array_class.cast(a));
    ^
  required: int[]
  found: Object
  reason: actual argument Object cannot be converted to int[] by method invocation conversion
3 errors

但是,通过反射传递对象可以正常工作并产生预期的结果.

Class of int[]  : class [I
Class of a      : class [I
int_array_class : class [I
a_class         : class [I
Class of values : class [I
5
Class of values : class [I
5
Class of values : class [I
5
Class of values : class [I
5

所以问题是：为什么编译器拒绝编译在运行时工作正常的三个命令指令？