Java IO.pdf - Nguyen Dang Binh

Java I/O
PushbackReader has two constructors, both of which take an underlying reader as an
argument. The first uses a one-character pushback buffer; the second sets the pushback buffer
to a specified size:
public PushbackReader(Reader in)
public PushbackReader(Reader in, int size)
The PushbackReader class has the usual collection of read() methods. These methods first
try to read the requested characters from the pushback buffer and only read from the
underlying reader if the pushback buffer is empty or has too few characters.
public int read() throws IOException
public int read(char[] text, int offset, int length) throws IOException
PushbackReader also has ready(), markSupported(), and close() methods:
public boolean ready() throws IOException
public boolean markSupported()
public void close() throws IOException
The ready() and close() methods merely invoke the ready() and close() methods of the
underlying reader. The markSupported() method returns false; pushback readers do not
support marking and resetting.
Three unread() methods push back specific characters. The first pushes back the character c;
the second pushes back the text array; the third pushes back the sub-array of text beginning
at offset and continuing for length chars.
public void unread(int c) throws IOException
public void unread(char[] text) throws IOException
public void unread(char[] text, int offset, int length) throws IOException
The unread characters aren't necessarily the same as the characters that were read. It would be
nicer if the PushbackReader itself kept track of which characters had been read, and all you
had to tell it was how many characters to unread. However, this approach does give the client
programmer the option of inserting tags or other data as the stream is read. The number of
characters you can push back onto the stream is limited by the size of the buffer set in the
constructor. Attempts to unread more characters than can fit in the buffer cause an
IOException to be thrown. An IOException is also thrown if you try to unread a closed
reader; once a PushbackReader has been closed, it can be neither read nor unread.
15.12 File Viewer Finis
As a final example of working with readers and writers, we return for the last time to the
FileDumper application last seen in Chapter 13. At that point, we had a GUI program that
allowed any file to be opened and interpreted in one of several formats, including ASCII,
decimal, hexadecimal, short, regular, and long integers in both big- and little-endian formats,
floating point, and double-precision floating point.
In this section we expand the program to read many different text formats besides ASCII. The
user interface must be adjusted to allow a binary choice of whether the file contains text or
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