CSCI 143 File IO

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CSCI 143File I/O
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Types of Data

• character data
• represented in 2-byte Unicode within Java
• represented as 1-byte ASCII in most files in US
• read with Reader subclasses
• written with Writer subclasses
• binary data
• read with InputStream subclasses
• written with OutputStream subclasses
• java.io package class hierarchy

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java.io package

• BufferedInputStream BufferedOutputStream
  BufferedReader BufferedWriter CharArrayReader
  CharArrayWriter DataInputStream
  DataOutputStream File FileDescriptor
  FileInputStream FileOutputStream
  FilePermission FileReader FileWriter
  FilterInputStream FilterOutputStream
  FilterReader FilterWriter InputStream

• InputStreamReader
• ObjectInputStream ObjectInputStream.GetField
  ObjectOutputStream ObjectOutputStream.PutField
  ObjectStreamClass ObjectStreamField
  OutputStream OutputStreamWriter PrintStream
  PrintWriter RandomAccessFile Reader
  SequenceInputStream SerializablePermission
  StreamTokenizer StringBufferInputStream
  StringReader StringWriter Writer

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Reading Character Data from a File

• class FileReader
• extends InputStreamReader which extends Reader
• constructor
• public FileReader (String fileName) throws
  FileNotFoundException
• important methods
• int read() throws IOException //reads a single
  character
• int read(char buf, int start, int len) throws
  IOException
• 
  // reads len characters
• returns -1 for EOF

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Reading Character Data

• BufferedReader extends Reader
• fills a buffer at a time for much greater
  efficiency
• constructor
• public BufferedReader (Reader reader)
• important methods
• String readLine() throws IOException //reads a
  single line
• returns null for EOF
• common usage (ignoring exceptions)
• BufferedReader rdr new BufferedReader (new
  FileReader (Grades.txt))
• String line
• while ((linerdr.readLine()) ! null) //
  process line

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Writing Character Data to a File

• class FileWriter
• extends OutputStreamWriter which extends Writer
• constructors
• public FileWriter (String fileName) throws
  IOException
• public FileWriter (String fileName, boolean
  append)throws IOException
• important methods
• void write(char c) throws IOException // writes
  a single char
• void write(char buf, int start, int len)
  throws IOException
• void write(String str, int start, int len)
  throws IOException
• void flush() throws IOException // forces
  output
• void close() throws IOException // flushes

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Writing Character Data

• BufferedWriter extends Writer
• writes a buffer at a time for much greater
  efficiency
• constructor
• public BufferedWriter (Writer writer)
• interesting methods
• void newLine() throws IOException //outputs a
  newline
• common usage (ignoring exceptions)
• BufferedWriter wrtr new BufferedWriter (new
  FileWriter(Grades.txt, true))
• String s Smith 2.0
• wrtr.write (s, 0, s.length())
• wrtr.newLine()
• wrtr.close()

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Writing Character Data

• PrintWriter extends Writer
• converts data to strings for output
• throws no exceptions
• constructors
• public PrintWriter (Writer writer)
• public PrintWriter (Writer writer, boolean
  autoflush)
• interesting methods
• void print(boolean b)//outputs a boolean as a
  string
• void print(int i) //outputs an int as a string
• void print(double d) //outputs a double as a
  string
• void print(String s) //outputs a String as a
  string
• void print(Object o) //outputs an Object as a
  string

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Writing Character Data

• PrintWriter (continued)
• common usage
• PrintWriter pwrtr new PrintWriter (new
  BufferedWriter (new FileWriter (Grades.txt,
  true)))
• String name Smith
• double grade 2.0
• pwrtr.print (name )
• pwrtr.println (grade)
• pwrtr.close()

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Reading Binary Data from a File

• class FileInputStream extends InputStream
• constructor
• public FileInputStream (String fileName) throws
  FileNotFoundException
• interesting methods
• int read() throws IOException //reads a single
  byte
• int read(byte buf, int start, int len) throws
  IOException // reads len bytes
• void close() throws IOException //closes the
  file
• returns -1 for EOF

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Reading Binary Data

• BufferedInputStream extends InputStream
• fills a buffer at a time for much greater
  efficiency
• constructor
• public BufferedInputStream (InputStream stream)
• common usage (ignoring exceptions)
• BufferedInputStream bis
• new BufferedInputStream (
• new FileInputStream (Grades.dat))

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Reading Binary Data

• DataInputStream extends FilterInputStream
• reads primitive data types
• constructor
• public DataInputStream (InputStream stream)
• interesting methods
• char readChar() throws IOException, EOFException
  
• int readInt() throws IOException, EOFException
  
• float readFloat() throws IOException,
  EOFException
• double readDouble() throws IOException,
  EOFException

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• DataInputStream dis null
• try
• //open stream
• dis new DataInputStream (
• new BufferedInputStream (
• new FileInputStream (Grades.dat)))
• catch (FileNotFoundException e)
• System.exit(1)
• try
• // read data
• while (true)
• double d dis.readDouble()
• System.out.println (d)

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Writing Binary Data to a File

• class FileOutputStream extends OutputStream
• constructors
• public FileOutputStream (String fileName) throws
  IOException
• public FileOutputStream (String fileName,
  boolean append) throws IOException
• interesting methods
• void write(int i) throws IOException // writes
  an int
• void write(byte buf) throws IOException
• void write(byte buf, int start, int len) throws
  IOException
• void flush() throws IOException // forces
  output
• void close() throws IOException // flushes

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Writing Binary Data

• BufferedOutputStream extends OutputStream
• writes a buffer at a time for much greater
  efficiency
• constructor
• public BufferedOutputStream (OutputStream
  writer)
• common usage (ignoring exceptions)
• BufferedOutputStream bos
• new BufferedOutputStream (
• new FileOutputStream (Grades.dat,
• true))

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Writing Binary Data

• DataOutputStream extends FilterOutputStream
• writes primitive data types
• constructor
• public DataOutputStream (OutputStream stream)
• interesting additional methods
• void writeChar(char c) throws IOException
• void writeInt(int i) throws IOException
• void writeFloat(float f) throws IOException
• void writeDouble(double d) throws IOException

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Interrogating a File

• class File
• represents a file or folder (directory)
• constructor
• public File (String path)
• public File (String path, String name)

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Interrogating a File

• Interesting methods
• boolean exists()
• boolean isDirectory()
• boolean isFile()
• boolean canRead()
• boolean canWrite()
• long length()

• long lastModified()
• boolean delete()
• boolean renameTo(File dest)
• boolean mkdir()
• String list()
• File listFiles()
• String getName()