InputStream & OutputStream V.S. Reader & Writer

常用的讀入操作方法：
1)BufferedReader in = new BufferedReader(new FileReader(filename));
2)DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream(filename)));
3)BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));

InputStream & OutputStream V.S. Reader & Writer
它們是二個不同的I/O體系，前者的出現先於後者。有適配器溝通二者：InputStreamReader & OutputStreamReader。
FileInputStream是InputStream的直接子類，BufferedInputStream和DataInputStream是FilterInputStream的直接子類。而FilterInputStream也是InputStream的直接子類，這個類的所有子類是用來拓展InputStream的屬性和接口，以提供一些方便的操作。