import javax.swing.*;
import java.beans.BeanDescriptor;
import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.util.Optional;

public class Test {

    public static void main(String[] args){
        try {
            // Returns: the name of the getter method in the annotated class, which returns the corresponding Swing container,
            BeanInfo info1 = Introspector.getBeanInfo(D.class);
            BeanDescriptor bd1 = info1.getBeanDescriptor();
            Optional.ofNullable(bd1.getValue("containerDelegate")).ifPresent(System.out::print);

            //or an empty string if the method name is not set.
            BeanInfo info2 = Introspector.getBeanInfo(T.class);
            BeanDescriptor bd2 = info2.getBeanDescriptor();
            Optional.ofNullable(bd2.getValue("containerDelegate")).ifPresent(System.out::print);  // null instead of empty string

        } catch (IntrospectionException e) {
            e.printStackTrace();
        }
    }
}

@SwingContainer()
class T {
}

@SwingContainer(delegate = "method")
class D {
}