Java: How to load a class (and its inner classes) that is already on the class path?

Question

How can I load a class that is already on the class path, instantiate it, and also instantiate any inner classes defined within it?

EG:

public class TestClass {


    public class InnerClass { }

}

Answer 1

Inner classes cannot exist outside the parent class. You need to construct the parent class first. Without reflection this would look like:

InnerClass innerClass = new TestClass().new InnerClass();

In reflection, you need to pass the parent class in during construction of the inner class.

Object testClass = Class.forName("com.example.TestClass").newInstance();
for (Class<?> cls : testClass.getClass().getDeclaredClasses()) {
    // You would like to exclude static nested classes 
    // since they require another approach.
    if (!Modifier.isStatic(cls.getModifiers())) {
        Object innerClass = cls
            .getDeclaredConstructor(new Class[] { testClass.getClass() })
            .newInstance(new Object[] { testClass });
    }
}