BufferedReader(Reader in)
BufferedReader(Reader in, int size)
void  close()
void  mark(int markLimit)
boolean markSupported()
int  read()
int  read(char[] buffer, int offset, int length)
String readLine()
boolean ready()
void  reset()
long  skip(long charCount) 

package java.io;
 public class BufferedReader extends Reader {
  private Reader in;
  // 字符缓冲区
  private char cb[];
  // nChars 是cb缓冲区中字符的总的个数
  // nextChar 是下一个要读取的字符在cb缓冲区中的位置
  private int nChars, nextChar;
  // 表示“标记无效”。它与UNMARKED的区别是：
  // (01) UNMARKED 是压根就没有设置过标记。
  // (02) 而INVALIDATED是设置了标记，但是被标记位置太长，导致标记无效！
 private static final int INVALIDATED = -2;
  // 表示没有设置“标记”
 private static final int UNMARKED = -1;
  // “标记”
  private int markedChar = UNMARKED;
  // “标记”能标记位置的最大长度
  private int readAheadLimit = 0; /* Valid only when markedChar > 0 */
  // skipLF(即skip Line Feed)是“是否忽略换行符”标记
  private boolean skipLF = false;
  // 设置“标记”时，保存的skipLF的值
  private boolean markedSkipLF = false;
  // 默认字符缓冲区大小
  private static int defaultCharBufferSize = 8192;
  // 默认每一行的字符个数
  private static int defaultExpectedLineLength = 80;
  // 创建“Reader”对应的BufferedReader对象，sz是BufferedReader的缓冲区大小
  public BufferedReader(Reader in, int sz) {
   super(in);
  if (sz <= 0)
   throw new IllegalArgumentException("Buffer size <= 0");
   this.in = in;
   cb = new char[sz];
  nextChar = nChars = 0;
  }
 // 创建“Reader”对应的BufferedReader对象，默认的BufferedReader缓冲区大小是8k
  public BufferedReader(Reader in) {
   this(in, defaultCharBufferSize);
  }
  // 确保“BufferedReader”是打开状态
  private void ensureOpen() throws IOException {
   if (in == null)
    throw new IOException("Stream closed");
  }
  // 填充缓冲区函数。有以下两种情况被调用：
  // (01) 缓冲区没有数据时，通过fill()可以向缓冲区填充数据。
  // (02) 缓冲区数据被读完，需更新时，通过fill()可以更新缓冲区的数据。
  private void fill() throws IOException {
   // dst表示“cb中填充数据的起始位置”。
   int dst;
   if (markedChar <= UNMARKED) {
   // 没有标记的情况，则设dst=0。
    dst = 0;
   } else {
    // delta表示“当前标记的长度”，它等于“下一个被读取字符的位置”减去“标记的位置”的差值；
    int delta = nextChar - markedChar;
    if (delta >= readAheadLimit) {
     // 若“当前标记的长度”超过了“标记上限(readAheadLimit)”，
     // 则丢弃标记！
     markedChar = INVALIDATED;
     readAheadLimit = 0;
    dst = 0;
    } else {
     if (readAheadLimit <= cb.length) {
      // 若“当前标记的长度”没有超过了“标记上限(readAheadLimit)”，
      // 并且“标记上限(readAheadLimit)”小于/等于“缓冲的长度”；
      // 则先将“下一个要被读取的位置，距离我们标记的置符的距离”间的字符保存到cb中。
     System.arraycopy(cb, markedChar, cb, 0, delta);
      markedChar = 0;
     dst = delta;
    } else {
     // 若“当前标记的长度”没有超过了“标记上限(readAheadLimit)”，
     // 并且“标记上限(readAheadLimit)”大于“缓冲的长度”；
     // 则重新设置缓冲区大小，并将“下一个要被读取的位置，距离我们标记的置符的距离”间的字符保存到cb中。
     char ncb[] = new char[readAheadLimit];
     System.arraycopy(cb, markedChar, ncb, 0, delta);
      cb = ncb;
     markedChar = 0;
      dst = delta;
     }
     // 更新nextChar和nChars
     nextChar = nChars = delta;
    }
   }
   int n;
   do {
    // 从“in”中读取数据，并存储到字符数组cb中；
    // 从cb的dst位置开始存储，读取的字符个数是cb.length - dst
    // n是实际读取的字符个数；若n==0(即一个也没读到)，则继续读取！
    n = in.read(cb, dst, cb.length - dst);
   } while (n == 0);
   // 如果从“in”中读到了数据，则设置nChars(cb中字符的数目)=dst+n，
   // 并且nextChar(下一个被读取的字符的位置)=dst。
   if (n > 0) {
    nChars = dst + n;
    nextChar = dst;
   }
  }
  // 从BufferedReader中读取一个字符，该字符以int的方式返回
  public int read() throws IOException {
   synchronized (lock) {
    ensureOpen();
    for (;;) {
     // 若“缓冲区的数据已经被读完”，
     // 则先通过fill()更新缓冲区数据
     if (nextChar >= nChars) {
      fill();
      if (nextChar >= nChars)
       return -1;
     }
     // 若要“忽略换行符”，
     // 则对下一个字符是否是换行符进行处理。
     if (skipLF) {
      skipLF = false;
      if (cb[nextChar] == '\n') {
       nextChar++;
       continue;
      }
     }
     // 返回下一个字符
     return cb[nextChar++];
    }
   }
  }
  // 将缓冲区中的数据写入到数组cbuf中。off是数组cbuf中的写入起始位置，len是写入长度
  private int read(char[] cbuf, int off, int len) throws IOException {
   // 若“缓冲区的数据已经被读完”，则更新缓冲区数据。
   if (nextChar >= nChars) {
    if (len >= cb.length && markedChar <= UNMARKED && !skipLF) {
     return in.read(cbuf, off, len);
    }
    fill();
   }
   // 若更新数据之后，没有任何变化；则退出。
   if (nextChar >= nChars) return -;
   // 若要“忽略换行符”，则进行相应处理
   if (skipLF) {
    skipLF = false;
    if (cb[nextChar] == '\n') {
     nextChar++;
     if (nextChar >= nChars)
      fill();
     if (nextChar >= nChars)
      return -1;
    }
   }
   // 拷贝字符操作
   int n = Math.min(len, nChars - nextChar);
   System.arraycopy(cb, nextChar, cbuf, off, n);
   nextChar += n;
   return n;
  }
  // 对read()的封装，添加了“同步处理”和“阻塞式读取”等功能
  public int read(char cbuf[], int off, int len) throws IOException {
   synchronized (lock) {
    ensureOpen();
    if ((off < 0) || (off > cbuf.length) || (len < 0) ||
     ((off + len) > cbuf.length) || ((off + len) < 0)) {
     throw new IndexOutOfBoundsException();
    } else if (len == 0) {
     return 0;
    }
    int n = read1(cbuf, off, len);
    if (n <= 0) return n;
    while ((n < len) && in.ready()) {
     int n1 = read1(cbuf, off + n, len - n);
     if (n1 <= 0) break;
     n += n1;
    }
    return n;
   }
  }
  // 读取一行数据。ignoreLF是“是否忽略换行符”
  String readLine(boolean ignoreLF) throws IOException {
   StringBuffer s = null;
   int startChar;
   synchronized (lock) {
    ensureOpen();
    boolean omitLF = ignoreLF || skipLF;
    bufferLoop:
    for (;;) {
     if (nextChar >= nChars)
      fill();
     if (nextChar >= nChars) { /* EOF */
     if (s != null && s.length() > 0)
       return s.toString();
      else
       return null;
     }
     boolean eol = false;
    char c = 0;
     int i;
     /* Skip a leftover '\n', if necessary */
     if (omitLF && (cb[nextChar] == '\n'))
      nextChar++;
     skipLF = false;
     omitLF = false;
    charLoop:
     for (i = nextChar; i < nChars; i++) {
      c = cb[i];
      if ((c == '\n') || (c == '\r')) {
       eol = true;
       break charLoop;
      }
     }
     startChar = nextChar;
     nextChar = i;
     if (eol) {
      String str;
      if (s == null) {
       str = new String(cb, startChar, i - startChar);
      } else {
       s.append(cb, startChar, i - startChar);
       str = s.toString();
      }
      nextChar++;
      if (c == '\r') {
       skipLF = true;
      }
      return str;
     }
     if (s == null)
      s = new StringBuffer(defaultExpectedLineLength);
     s.append(cb, startChar, i - startChar);
    }
   }
  }
  // 读取一行数据。不忽略换行符
  public String readLine() throws IOException {
   return readLine(false);
  }
  // 跳过n个字符
  public long skip(long n) throws IOException {
   if (n < 0L) {
    throw new IllegalArgumentException("skip value is negative");
   }
   synchronized (lock) {
    ensureOpen();
    long r = n;
   while (r > 0) {
     if (nextChar >= nChars)
      fill();
     if (nextChar >= nChars) /* EOF */
      break;
     if (skipLF) {
      skipLF = false;
      if (cb[nextChar] == '\n') {
       nextChar++;
      }
     }
     long d = nChars - nextChar;
     if (r <= d) {
      nextChar += r;
      r = 0;
      break;
     }
     else {
      r -= d;
      nextChar = nChars;
     }
    }
    return n - r;
   }
  }
  // “下一个字符”是否可读
  public boolean ready() throws IOException {
   synchronized (lock) {
    ensureOpen();
    // 若忽略换行符为true；
    // 则判断下一个符号是否是换行符，若是的话，则忽略
    if (skipLF) {
     if (nextChar >= nChars && in.ready()) {
      fill();
     }
     if (nextChar < nChars) {
      if (cb[nextChar] == '\n')
       nextChar++;
      skipLF = false;
     }
    }
    return (nextChar < nChars) || in.ready();
   }
  }
  // 始终返回true。因为BufferedReader支持mark(), reset()
  public boolean markSupported() {
   return true;
  }
  // 标记当前BufferedReader的下一个要读取位置。关于readAheadLimit的作用，参考后面的说明。
  public void mark(int readAheadLimit) throws IOException {
   if (readAheadLimit < 0) {
   throw new IllegalArgumentException("Read-ahead limit < 0");
   }
   synchronized (lock) {
    ensureOpen();
    // 设置readAheadLimit
    this.readAheadLimit = readAheadLimit;
    // 保存下一个要读取的位置
    markedChar = nextChar;
    // 保存“是否忽略换行符”标记
    markedSkipLF = skipLF;
   }
  }
  // 重置BufferedReader的下一个要读取位置，
  // 将其还原到mark()中所保存的位置。
  public void reset() throws IOException {
   synchronized (lock) {
    ensureOpen();
   if (markedChar < 0)
     throw new IOException((markedChar == INVALIDATED)
          ? "Mark invalid"
          : "Stream not marked");
    nextChar = markedChar;
    skipLF = markedSkipLF;
   }
  }
  public void close() throws IOException {
   synchronized (lock) {
    if (in == null)
     return;
    in.close();
    in = null;
    cb = null;
   }
  }
 }

 private void fill() throws IOException {
  int dst;
  if (markedChar <= UNMARKED) {
   /* No mark */
   dst = 0;
  } else {
   /* Marked */
   int delta = nextChar - markedChar;
   if (delta >= readAheadLimit) {
    /* Gone past read-ahead limit: Invalidate mark */
    markedChar = INVALIDATED;
    readAheadLimit = 0;
    dst = 0;
   } else {
    if (readAheadLimit <= cb.length) {
     /* Shuffle in the current buffer */
    System.arraycopy(cb, markedChar, cb, 0, delta);    
 markedChar = 0;
     dst = delta;
    } else {
     /* Reallocate buffer to accommodate read-ahead limit */
     char ncb[] = new char[readAheadLimit];
    System.arraycopy(cb, markedChar, ncb, 0, delta);
     cb = ncb;
     markedChar = 0;
     dst = delta;
    }
    nextChar = nChars = delta;
   }
  }
  int n;
  do {
   n = in.read(cb, dst, cb.length - dst);
  } while (n == 0);
 if (n > 0) {
   nChars = dst + n;
   nextChar = dst;
  }
 }

private void fill() throws IOException {
  int dst;
  if (markedChar <= UNMARKED) {
   /* No mark */
   dst = 0;
  } 
  int n;
  do {
   n = in.read(cb, dst, cb.length - dst);
  } while (n == 0);
  if (n > 0) {
   nChars = dst + n;
   nextChar = dst;
  }
 }

private void fill() throws IOException {
  int dst;
  if (markedChar > UNMARKED) {
   int delta = nextChar - markedChar;
   if (delta >= readAheadLimit) {
    markedChar = INVALIDATED;
    readAheadLimit = 0;
    dst = 0;
   } 
  }
  int n;
  do {
   n = in.read(cb, dst, cb.length - dst);
  } while (n == 0);
 if (n > 0) {
   nChars = dst + n;
   nextChar = dst;
  }
 }

 private void fill() throws IOException {
  int dst;
  if (markedChar > UNMARKED) {
   int delta = nextChar - markedChar;
   if ((delta < readAheadLimit) && (readAheadLimit <= cb.length) ) {
    System.arraycopy(cb, markedChar, cb, 0, delta);
    markedChar = 0;
    dst = delta;
    nextChar = nChars = delta;
   }
  }
  int n;
  do {
   n = in.read(cb, dst, cb.length - dst);
 } while (n == 0);
  if (n > 0) {
   nChars = dst + n;
   nextChar = dst;
  }
 }

private void fill() throws IOException {
  int dst;
  if (markedChar > UNMARKED) {
   int delta = nextChar - markedChar;
   if ((delta < readAheadLimit) && (readAheadLimit > cb.length) ) {
    char ncb[] = new char[readAheadLimit];
    System.arraycopy(cb, markedChar, ncb, 0, delta);
    cb = ncb;
    markedChar = 0;
    dst = delta;
    nextChar = nChars = delta;
   }
  }
  int n;
  do {
   n = in.read(cb, dst, cb.length - dst);
  } while (n == );
  if (n > ) {
   nChars = dst + n;
   nextChar = dst;
  }
 }

 import java.io.BufferedReader;
 import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.InputStream;
 import java.io.FileReader;
 import java.io.IOException;
 import java.io.FileNotFoundException;
 import java.lang.SecurityException;
 /**
 * BufferedReader 测试程序
 *
 * 
 */
 public class BufferedReaderTest {
  private static final int LEN = 5;
  public static void main(String[] args) {
   testBufferedReader() ;
  }
  /**
  * BufferedReader的API测试函数
  */
  private static void testBufferedReader() {
   // 创建BufferedReader字符流，内容是ArrayLetters数组
   try {
    File file = new File("bufferedreader.txt");
    BufferedReader in =
     new BufferedReader(
      new FileReader(file));
    // 从字符流中读取5个字符。“abcde”
   for (int i=0; i<LEN; i++) {
     // 若能继续读取下一个字符，则读取下一个字符
     if (in.ready()) {
      // 读取“字符流的下一个字符”
      int tmp = in.read();
      System.out.printf("%d : %c\n", i, tmp);
     }
    }
    // 若“该字符流”不支持标记功能，则直接退出
    if (!in.markSupported()) {
     System.out.println("make not supported!");
     return ;
    }
    // 标记“当前索引位置”，即标记第6个位置的元素--“f”
   // 1024对应marklimit
    in.mark(1024);
   // 跳过22个字符。
    in.skip(22);
    // 读取5个字符
    char[] buf = new char[LEN];
   in.read(buf, 0, LEN);
    System.out.printf("buf=%s\n", String.valueOf(buf));
    // 读取该行剩余的数据
    System.out.printf("readLine=%s\n", in.readLine());
    // 重置“输入流的索引”为mark()所标记的位置，即重置到“f”处。
    in.reset();
   // 从“重置后的字符流”中读取5个字符到buf中。即读取“fghij”
    in.read(buf, , LEN);
    System.out.printf("buf=%s\n", String.valueOf(buf));
    in.close();
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  } catch (SecurityException e) {
   e.printStackTrace();
  } catch (IOException e) {
   e.printStackTrace();
  }
  }
 }

abcdefghijklmnopqrstuvwxyz
0123456789
ABCDEFGHIJKLMNOPQRSTUVWXYZ

0 : a
1 : b
2 : c
3 : d
4 : e
buf=01234
readLine=56789
buf=fghij