PushbackInputStream

The PushbackInputStream class provides a pushback buffer so a program can "unread" bytes onto the stream.

The next time data is read from the stream, the "unread" bytes are read.

 public void unread(int b) throws IOException
 public void unread(byte[] data, int offset, int length) throws IOException
 public void unread(byte[] data) throws IOException

By default the buffer is only one byte long, and trying to unread more than that throws an IOException. However you can change the default buffer size with the second constructor:
```
 public PushbackInputStream(InputStream in)
 public PushbackInputStream(InputStream in, int size)
```

Although both PushbackInputStream and BufferedInputStream use buffers, only a PushbackInputStream allows unreading and only a BufferedInputStream allows marking and resetting. In a PushbackInputStream markSupported() returns false.

The read() and available() methods work exactly as with normal input streams. However, they first attempt to read from the pushback buffer.