Dynamically converting java object of Object class to a given class when class name is known

Question

Yeah, I know. Long title of question... So I have class name in string. I'm dynamically creating object of that class in this way:

String className = "com.package.MyClass";   
Class c = Class.forName(className);
Object obj = c.newInstance();

How I can dynamically convert that obj to MyClass object? I can't write this way:

MyClass mobj = (MyClass)obj;

...because className can be different.

Answer 1

you don't, declare an interface that declares the methods you would like to call:

public MyInterface
{
  void doStuff();
}

public class MyClass implements MyInterface
{
  public void doStuff()
  {
    System.Console.Writeln("done!");
  }
}

then you use

MyInterface mobj = (myInterface)obj;
mobj.doStuff();

If MyClassis not under your control then you can't make it implement some interface, and the other option is to rely on reflection (see this tutorial).

Answer 2

If you didnt know that mojb is of type MyClass, then how can you create that variable?

If MyClass is an interface type, or a super type, then there is no need to do a cast.

Answer 3

You don't have to convert the object to a MyClass object because it already is. Wnat you really want to do is to cast it, but since the class name is not known at compile time, you can't do that, since you can't declare a variable of that class. My guess is that you want/need something like "duck typing", i.e. you don't know the class name but you know the method name at compile time. Interfaces, as proposed by Gregory, are your best bet to do that.