package singleton;
public class AppConfig {

    private AppConfig() {
        System.out.println("Reading configuration from file...");
    }

    private static class Holder {
        static final AppConfig INSTANCE = new AppConfig();
    }

    public static AppConfig getInstance() {
        return Holder.INSTANCE;
    }

    public String getProperty(String key) {
        return System.getProperty(key, "(not set)");
    }
}