Streams and Readers The stream hierarchy is for reading bytes, the - - PowerPoint PPT Presentation

Duke CPS 108

• 25. 1

Streams and Readers

• The stream hierarchy is for reading bytes, the reader/writer

hierarchy is for reading characters

➤ Unicode characters can be used internationally, variety of

languages/characters, the future beyond ASCII

➤ bytes are used on most machines for external storage,

convenient also for storing raw objects/values, e.g., int stored as 0x000000ff vs “255”

• More than 50 input/output streams readers/writers

➤ many are specialized, good to know that they’re there, but

how can you pick which one to use?

➤ Examples: raw, RandomAccess, Buffered, PushBack, Zip,

StringBuffer, Object, File, ...

Duke CPS 108

• 25. 2

Streams

• InputStream get raw bytes from a source

➤ source could be URL, File, Pipe, String, … ➤ one abstract method, must be implemented, returns byte or

• 1 if no more data, this method blocks

public abstract int read() throws IOException

➤ other read methods implemented in terms of read(), e.g.,

read(byte b[]) and read(byte b[], int offset, int length)

• OutputStream is similar, writes raw bytes

➤ one abstract method, two others similar to InputStream

public abstract void write(int b) throws IOException

• Parameters and variables can be bound to concrete

implementations of these abstract classes

Duke CPS 108

• 25. 3

Chaining Streams

• Read doubles, use buffering, from a file

DataInputStream input = new DataInputStream( new BufferedInputStream( new FileInputStream(“numbers.dat”))); double d = input.readDouble();

• What about reading from a gzip’d file, use GZIPInputStream,

from java.util.zip

• What about reading from a URL?, use URL class in java.net

(URL.openStream()).

Duke CPS 108

• 25. 4

Readers/Writers for Unicode

• Writing text (as opposed to bytes) can be done with the

PrintWriter class

➤ has print(Foo f) method for all built-in types, for String,

and for Object

➤ wrapper for other Writer objects and for OutputStreams

• Reading text can be done with a BufferedReader (for line
• riented text)

➤ bind the reader to a FileReader or an InputStream of

appropriate type

➤ use InputStreamReader as bridge between streams and

readers

• specify character encoding here, e.g., 8859_7, which is ISO

Latin/Arabic