使用反射提供的参数值调用构造器

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import static java.lang.System.out;

class EmailAliases {
    private Set<String> aliases;

    private EmailAliases(HashMap<String, String> h) {
        aliases = h.keySet();
    }

    public void printKeys() {
        out.format("Mail keys:%n");
        for (String k : aliases)
            out.format("  %s%n", k);
    }
}

public class RestoreAliases {

    private static Map<String, String> defaultAliases = new HashMap<String, String>();
    static {
        defaultAliases.put("Duke", "duke@i-love-java");
        defaultAliases.put("Fang", "fang@evil-jealous-twin");
    }

    public static void main(String... args) {
        try {
            Constructor ctor = EmailAliases.class
                    .getDeclaredConstructor(HashMap.class);
            ctor.setAccessible(true);
            EmailAliases email = (EmailAliases) ctor
                    .newInstance(defaultAliases);
            email.printKeys();

            // production code should handle these exceptions more gracefully
        } catch (InstantiationException x) {
            x.printStackTrace();
        } catch (IllegalAccessException x) {
            x.printStackTrace();
        } catch (InvocationTargetException x) {
            x.printStackTrace();
        } catch (NoSuchMethodException x) {
            x.printStackTrace();
        }
    }
}