class BaseFile
{ 
	//欄位、屬性、建構函式、函式、索引器
	//私有欄位
	private string _filePath;
	public string FilePath  //快捷鍵 ctrl+R+E
	{
		get { return _filePath; }
		set { _filePath = value; }
	}

	//自動屬性   快捷鍵 prop+兩下tab
	public string FileName { get; set; }

	//建構函式
	public BaseFile(string filePath, string fileName)
	{
		this.FilePath = filePath;
		this.FileName = fileName;
	}
      
	//設計一個函式  用來開啟指定的檔案
	public void OpenFile()
	{
		ProcessStartInfo psi = new ProcessStartInfo(this.FilePath + "\\" + this.FileName);
		Process pro = new Process();
		pro.StartInfo = psi;
		pro.Start();
	}
}
 

    class TxtFile : BaseFile
    { 
        //因為子類會預設呼叫父類無引數的建構函式

        public TxtFile(string filePath, string fileName) : base(filePath, fileName)
        { }
    }