Loading a Class from a String

Question

I want to instantiate a class by the value of a String. I found several tutorials that show several methods for doing this. The class MUST inherit from a certain interface

Answer 1

What you have may work, but you don't have to load the class using the same classloader that loaded ImplementMe. This should work equally well:

Object newInstance = this.getClass().getClassLoader().loadClass("my.package.IImplementedYou").newInstance();

The important thing is that the classloader knows both the class file with the implementation of "my.package.IImplementedYou" and the class with the implementation of "ImplementMe".

You may explicitly check that IImplementedYou really implements ImplementMe like this:

if(newInstance instanceof my.package.IImplementedYou) {  
    ((ImplementMe)newInstance).runMe(); 
}

You may also check that IImlementedYou really is implementing the interface before creating the instance:

Class c = this.getClass().getClassLoader().loadClass("my.package.IImplementedYou");
if(ImplementMe.class.isAssignableFrom(c)) {
    Object newInstance = c.newInstance(); 
}