Transcript ch04-Data Streams(3)

Data streams(3)
Readers and Writers
Readers and Writers
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java.io.Reader class: a character-based
equivalent of the java.io.InputStream class.
Character-oriented
A better alternative than input streams and
output streams when used on text data.
To better support the Unicode character
streams.
What are Unicode characters?
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ASCII characters
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Unicode characters
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composed of 8 bits
offering a range of 256 possible characters
presented by 16 bits
allowing for a maximum of 65536 possible characters
UTF-8
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a modified form of Unicode encoding
A variable-width encoding format; some characters are a
single byte and others multiple bytes.
The java.io.Reader class
The java.io.Reader class
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Methods
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void close()
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int read()
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int read(char[] characterArray)
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reads and returns a chracter.
populates an array of characters with data.
boolean ready()
- returns “true” if there is data available.
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The java.io.Reader class
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Low-level readers
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CharArrayReader
FileReader
PipedReader
StringReader
InputStreamReader
Filter readers
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BufferedReader
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Low-level Readers
Low-level readers*
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CharArrayReader
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FileReader
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Reads a sequence of characters from a thread
communication pipe, like a PipedInputStream
StringReader
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Reads from a file, just like a FileInputStream
PipedReader
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Reads from a character array
Reads a sequence of characters from a string, as if it
were a StringBufferInputStream
InputStreamReader
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Bridges the divide between an input stream and a reader,
by reading from the input stream.
CharArrayReader*
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Constructors
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CharArrayReader(char[] charArray)
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creates a character array reader that will
operate on the specified array.
CharArrayReader(char[] charArray, int
offset, int length)
FileReader*
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Constructors
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FileReader(File file)
- creates a reader that will access the contents of the
specified file object.
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FileReader(String filename)
- … the specified filename
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FileReader(FileDescriptor descriptor)
- … the specified descriptor handle
PipedReader*
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Constructors
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PipedReader()
- creates an unconnected pipe reader
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PipedReader(PipedWriter writer)
- creates a connected pipe that will read the output of
the specified writer
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Methods
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void connect(PipedWriter writer)
- connects the reader to the specified writer
StringReader*
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Constructor
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StringReader(String stringToBeRead)
- reads from the beginning of the specified string until
the end
InputStreamReader
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Constructors
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InputStreamReader(InputStream input)
- connects an input stream to the reader
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InputStreamReader(InputStream input, String encoding)
- … using the specified encoding form
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Methods
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String getEncoding()
- returns the name of the character encoding used by this stream
Filter readers
BufferedReader
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Constructors
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BufferedReader(Reader reader)
- reads data from the specified reader into a buffer
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BufferedReader(Reader reader, int bufferSize)
Methods
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String readLine()
- reads a line of text form the underlying stream.
The line is terminated by a line separator, such
as a carriage return/linefeed.
Code for
InputStreamToReaderDemo
The java.io.Writer class
The java.io.Writer class
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Methods
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void close()
void flush()
- flushes any unsent data.
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void
void
void
void
void
write(int character)
write(char[] charArray)
write(char[] charArray, int offset, int length)
write(String string)
write(String string, int offset, int length)
The java.io.Writer class
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Low-level writers
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CharArrayWriter
FileWriter
PipedWriter
StringWriter
OutputStreamWriter
Filter writers
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BufferedWriter
PrintWriter
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Low-level Writers
Low-level writers*
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CharArrayWriter
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FileWriter
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Writes characters to a thread communication pipe
StringWriter
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Writes to a local file
PipedWriter
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Writes to a variable length character array (and resizes
as characters are added)
Writes characters to a string buffer
OutputStreamWriter
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Writes to a legacy output stream
CharArrayWriter*
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……
Code for
OutputStreamToWriterDemo
Filtered Writers
BufferedWriter
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Constructors
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BufferedWriter(Writer writer)
- creates a buffered writer, connected to a specified
writer
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BufferedWriter(Writer writer, int bufferSize)
- … with a buffer of the specified size
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Methods
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No methods
PrintWriter
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The sister class of the PrintStream, and provides
the same methods for writing datatypes as text.
Constructors
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PrintWriter(Writer writer)
- creates a print writer, writing to the specified writer
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PrintWriter(Writer writer, boolean flushFlag)
- auto-flush whenever a println method or a line separator is sent
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Methods
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void print()
void println()