Question

How I can get constructor reflectively, if its param is Object ... objects.

My constructor:

  public MyClass ( Object ... objects )
  {
    if ( ! ( objects == null ) )
    {
      if ( objects.length > 0 && objects [ 0 ] instanceof Long )
      {
        setLatency ( ( Long ) objects [ 0 ] ) ;
      }
    }
  }

How I get it now:

Class< ? > clazz = Class.forName ( "MyClass" ) ;

Constructor< ? > clazzConstructor = clazz.getConstructor ( Object [ ].class ) ;

What I try to do:

Long latency = 1000L ;

MyClass myInstance = ( MyClass ) clazzConstructor.newInstance ( latency ) ;

And I get
java.lang.IllegalArgumentException: argument type mismatch

If latency == null, everything works.

Answer 1

Your constructor is expecting an object array but you’re passing a single Long to it.

Wrapping latency into an object array will work, although be careful as newInstance() itself is expecting Object ..., and if you pass it nothing but an Object[], it will interpret it as a list of arguments. So you’ll have to do something like this:

MyClass myInstance = ( MyClass ) clazzConstructor.newInstance ( (Object)new Object[] { latency } ) ;

or

MyClass myInstance = ( MyClass ) clazzConstructor.newInstance ( new Object[] { new Object[] { latency } } ) ;

The first one “fools” the compiler into wrapping your object array into another, the second one does it explicitly instead.

(Passing null only worked because null is null, no matter what the declared type of the parameter is.)