public static void main(String[] args) {
        // һżĹ
        LetterProcess letterProcess = new LetterProcessImpl();
        // ʼд
        letterProcess.writeContext("Hello,It's me,do you know who I am? I'm your old lover. I'd like to....");
        // ʼдŷ
        letterProcess.fillEnvelope("Happy Road No. 666,God Province,Heaven");
        // ŷŵŷװ
        letterProcess.letterInotoEnvelope();
        // ܵʾְ䣬Ͷ
        letterProcess.sendLetter();

        // ִʾ֣ʾƽHell Road
        ModenPostOffice hellRoadPostOffice = new ModenPostOffice();
        // ֻҪŵݺ˵ַһϵеĹ
        String address = "Happy Road No. 666,God Province,Heaven"; // һַ
        String context = "Hello,It's me,do you know who I am? I'm your old lover. I'd like to....";
        hellRoadPostOffice.sendLetter(context, address);
    }