MELJUN CORTES JAVA_IO

8/10/2019 MELJUN CORTES JAVA_IO

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Java I/O

Streams, Readers, Writers, Buffers andFiles

MELJUN CORTES MBA MPA BSCS


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What is a stream?


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What is a stream?

Websters Dictionary:stream, n: [2b.] a constantly renewedsupply


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What is a stream?

- Object that represents data beingdelivered to or from an object.


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What is a stream?

- Object that represents data beingdelivered to or from an object.

- Behavior: One byte at a time or onecharacter at a time.


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What is a stream?

-- code example:


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What is a reader/writer?


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There are actually two kinds of streams:


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There are actually two kinds of streams:Byte Streams


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There are actually two kinds of streams:Byte Streams read/write raw bytes


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There are actually two kinds of streams:Byte Streams read/write raw bytesCharacter Streams (readers, writers)


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There are actually two kinds of streams:Byte Streams read/write raw bytesCharacter Streams (readers, writers) read/write characters (16-bit unicode)


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Two Kinds of Streams


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Hierarchies do not overlap:


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Hierarchies do not overlap:


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Buffering


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Buffering

Accessing anything outside of memory(disk, network, web) is expensive.


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Buffering

Accessing anything outside of memory(disk, network, web) is expensive. Better to access a big lump at a time thanone byte/char at a time.


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Buffering

-- Code example


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LineNumberReader


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LineNumberReader

A buffered character -input stream thatkeeps track of line numbers.


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LineNumberReader

setLineNumber() does not seek to a line inthe file. It just designates the line numberof the first line.


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LineNumberReader

BufferedReader also has a readLine()method. Use that if you dont need tokeep track of line number.


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InputStreamReader


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InputStreamReader

Converts bytes from an InputStream tochars, using the proper encoding.


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PrintWriter

System.out is a PrintWriter


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PrintWriter

Print formatted representations ofobjects to a text- output stream.


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PrintWriter

Print formatted representations ofobjects to a text- output stream. ex. print(boolean), print(char), print(long),println( Auto-flush on newline (default behavior).


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PrintWriter

Print formatted representations ofobjects to a text- output stream. ex. print(boolean), print(char), print(long),println( Auto-flush on newline (default behavior).Can wrap a Writer or an OuputStream.


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Using Streams on the Web


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Using Streams on the Web

Code examples:Reading from a URL object.Reading from a URLConnection object.Writing to a URLConnection objectWriting to a HttpServletResponse object.


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File


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File

Just a wrapper for a String, does notnecessarily denote something on the filesystem.


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File

Just a wrapper for a String, does notnecessarily denote something on the filesystem.ex: new File(I dont friggin care if this isa valid filename.); will compile.


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File

ConstructorsCreating & deleting filesCreating temp files and deleting on exitMoving, renaming and copyingOther useful File methodsPerformance issue with regards to usingFile methods


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File

Code example: Using FilenameFilter

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MELJUN CORTES JAVA_IO