public class BufferedReader extends Reader {

    //该属性可以封装一个任意的Reader的子类
    private Reader in;
    //添加了缓冲区，提高了写数据的效率
    private char cb[];
    private int nChars, nextChar;
    
    ... ...

public class BufferedWriter extends Writer {

    //有了该属性，可以封装任意一个Writer的子类
    private Writer out;
    //添加了缓冲区，提高了写数据的效率
    private char cb[];
    private int nChars, nextChar;

    ... ...