java: how to get singleton instance by classloader

Question

Assume, I load the class by the ClassLoader at the runtime:

Class<MyInterface> clazz = (Class<MyInterface>)getClass().getClassLoader().loadClass("ImplementerOfMyInterface");

The new instance I can create then by

MyInterface myInt = clazz.newInstance();

But when I need to get the instance of the singleton by its name that implements the MyInterface instead of creating the new one, what should be done?

Answer 1

Instead of invoking newInstance , you could invoke a static "getInstance" method (or whatever singleton getter method name you use).

For example:

public class ReflectTest {

    public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("ReflectTest");
        Method m = clazz.getDeclaredMethod("getInstance", null);
        Object o = m.invoke(null, null);
        System.out.println(o == INSTANCE);
    }

    public static ReflectTest getInstance() {
        return INSTANCE;
    }

    private static final ReflectTest INSTANCE = new ReflectTest();

    private ReflectTest() {
    }

}