package singleton;

public class AppConfigHolder {

    private AppConfigHolder() { /* load config */ }

    // The JVM loads Holder only when getInstance() is first called.
    // Class loading is inherently thread-safe — the JVM ensures it happens once.
    // No synchronized, no volatile, no locks — just the JVM class loading guarantee.
    private static class Holder {
        static final AppConfigHolder INSTANCE = new AppConfigHolder();
    }

    public static AppConfigHolder getInstance() {
        // This reference triggers Holder to load (if it hasn't already).
        // After first call, Holder is already loaded and this is just a field read.
        return Holder.INSTANCE;
    }
}