public static void w(String format, Object... args) {
        checkInitialization();
        sLogger.w(format, args);
    }
Log a message with level {@link LogLevel#WARN}.

@param format the format of the message to log
@param args   the arguments of the message to log
android/android_framework/base/src/main/java/com/elvishew/xlog/XLog.java