How do I manage dynamic narrowing casts without instanceof?

Question

Hi all,
I need to extract arbitrary Objects from a given Collection and cast them to their original types. The problem is: checking with instanceof won't work for me, because the number of possible types is practically unlimited. Can anybody help?
Thanks in advance,
Wolfgang

Answer 1

I don't think you have to do the cast in the set method. The following code works for me:
[Main is a simple class with attributes <String a>, <int b> and <Main c>, and has getters for them]
Note that the code is not nice, it's just a quick-n-dirty test case I wrote in a few minutes.
Note also that I use Objects in the set method, rather then a String, an Integer and a Main.
      Class mainClass = Class.forName("dynamicinstantiation.Main");
      Constructor ctr = mainClass.getConstructor(new Class[0]);
      // object of class main, not known to the client
      Object main = ctr.newInstance(new Object[0]);
      // fieldvalues to set
      Object a = "String";
      Object b = new Integer(100);
      Object c = new Main();
      // get fields
      Field fldA = main.getClass().getDeclaredField("a");
      Field fldB = main.getClass().getDeclaredField("b");
      Field fldC = main.getClass().getDeclaredField("c");
      fldA.set(main, a);
      fldB.set(main, b);
      fldC.set(main, c);
      // Cast main to Main class, so we;re able to access it's methods
      Main m = (Main)main;
      System.out.println(m.getA());
      System.out.println(m.getB());
      System.out.println(m.getC().getA());
      System.out.println(m.getC().getB());