Class.newInstance invokes the no-arg constructor (the one that doesn’t take any parameters). In order to invoke a different constructor, you need to use the reflection package (java.lang.reflect).
Get a Constructor instance like this:
Class<?> cl = Class.forName("javax.swing.JLabel");
Constructor<?> cons = cl.getConstructor(String.class);
The call to getConstructor specifies that you want the constructor that takes a single String parameter. Now to create an instance:
Object o = cons.newInstance("JLabel");
And you’re done.
P.S. Only use reflection as a last resort!