Question

I am trying to load a final class using the follwoing code

final ClassLoader myClassLoader = ClassLoader.getSystemClassLoader();
final String classNameToBeLoaded = "demo";
final Class myClass = myClassLoader.loadClass(classNameToBeLoaded);
    // create a new instance
final Constructor cons = demo.class.getConstructor();......(1)
final Object whatInstance = cons.newInstance();

it’s returning me no such method exception…at 1.What the problem…?

Answer 1

final Constructor cons = demo.class.getConstructor();

If this fails, this means one of two things:

either there’s no default constructor or it’s not public (class.getConstructor(...) only returns public constructors and if there was a public default constructor, you wouldn’t be doing this in the first place).

You can solve the second problem by using getDeclaredConstructor(...) instead of getConstructor(), it finds constructors with all visibilities:

final Constructor<Demo> cons = demo.class.getDeclaredConstructor();
Demo demo = cons.newInstance();

The first problem is tougher, obviously 🙂