Thread-safe Singleton

AppConfig.java

public class AppConfig {

    private static AppConfig INSTANCE = null;
    private Context context;

    private AppConfig(Context context) {
        this.context = context;
    }

    public static AppConfig get(Context context) {
        if (INSTANCE == null) {
            synchronized (AppConfig.class) {
                if (INSTANCE == null) {
                    INSTANCE = new AppConfig(context);
                }
            }
        }
        return INSTANCE;
    }
}