CTEC 1641 Enterprise Computing II

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CTEC 1641Enterprise Computing II
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Exercise 1

• Using the following helper code, build a vehicle
  class. Include at least the attributes
• Speed
• Colour
• OnOff
• Write a method to turn the car on and off, and
  updates the OnOff boolean.
• Write a method called ChangeSpeed which increases
  and decreases the speed by adding/subtracting the
  attribute.
• Add a constructor to take the attributes as
  arguments
• Demonstrate both of these methods using your
  main() method.

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• public class CTEC1641_Lecture4_HelperCode
• //Some attribues
• String Attribute1"BooRa"
• Double ABigOleDecimal12.4
• public int Amethod(String SomethingToSay)
• System.out.println("I am saying something "
  SomethingToSay)
• int TheReturnVar3
• return TheReturnVar //Let's return a
  value
• public static void main( String args )
• System.out.println( "Hello, Cruel World!" )
• //Create the object
• CTEC1641_Lecture4_HelperCode SomeOldObject
  new CTEC1641_Lecture4_HelperCode()

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public class CTEC1641_Lecture4_Exercise1 //Some
attributes double Speed String
Colour boolean OnOff //Base
constructor CTEC1641_Lecture4_Exercise1()
Speed 0.0 //Speed of the car.
Initially zero Colour "red" //Tis' be
a red car OnOff false //Set the car
to off initially //Another
constructor CTEC1641_Lecture4_Exercise1(double
ASpeed, String AColour, boolean CarOn)
Speed ASpeed Colour
AColour OnOff CarOn public static
void main( String args ) //Create the
object using the base constructor CTEC1641_Lectu
re4_Exercise1 TheCar new CTEC1641_Lecture4_Exerc
ise1() //Display the attributes of the
object System.out.println("---The Object
Status---") System.out.println(TheCar.Speed)
System.out.println(TheCar.Colour) System.out.p
rintln(TheCar.OnOff) System.out.println("------
-----------------") //Create the object
using another constructor CTEC1641_Lecture4_Exer
cise1 AnotherCar new CTEC1641_Lecture4_Exercise1
(65.4,"Blue",false)
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//Display the attributes of the
object System.out.println("---The Object
Status---") System.out.println(AnotherCar.Speed
) System.out.println(AnotherCar.Colour) Syst
em.out.println(AnotherCar.OnOff) System.out.pri
ntln("-----------------------") //Lets start
the car up TheCar.TurnCarOnOff() System.out.p
rintln("Car OnOff " TheCar.OnOff) //Chang
e the speed of the car from 0 to
55.4 TheCar.Speed TheCar.ChangeSpeed(55.4)
System.out.println("The Speed of the car is
"TheCar.Speed) //Lets change the car
again TheCar.Speed TheCar.ChangeSpeed(-4.3)
System.out.println("The Speed of the car is
"TheCar.Speed) public void
TurnCarOnOff() if (OnOff true)
//If the car is already on OnOff false
//Set the car to off else
OnOff true //Set the car to
on public double ChangeSpeed(double
SpeedChange) double NewSpeed Speed
//Initialize our working variable NewSpeed
NewSpeed SpeedChange return NewSpeed
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I/O

• Java implements much of its communications
  within the java.io package (import java.io.)
• Data is read and written using the concept of
  streams.
• Two types of streams
• Input data from a source into a program
• Output data to a source from the program

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Streams - Overview

• Basic process
• Create an object associated with the data source
  (i.e. FileInputStream, InputReaderStream)
• Work with the stream using various methods (i.e.
  BufferReader, BufferWriter)
• Close down the stream to release the resource. In
  virtually all cases use the close() method
• Sometime filters can be applied to a stream to do
  some additional processing. This is done by
  associating a filter to the stream.

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I/O Exceptions

• When using the java.io package , any exceptions
  generated will be of the type IOException, some
  common subclasses are
• EOFException
• FileNotFound
• Ensure that at the very least you catch
  IOException using a try-catch

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File Paths

• Paths are platform specific
• (i.e. c\\temp\\Boo.txt, /temp/Boo.txt)
• Java also allows a more machine independent way
  to represent paths File.Separator
• String AFineSepCharacter File.separator
• The separator character can be concatenated with
  the path in order to build machine independent
  paths

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File Input - Byte

• If the file is a binary file, or we just want to
  read bytes (i.e. ASCII)
• FileInputStream TheFile new FileInputStream("Th
  eGoods.dat")
• Use the read() method to read in a byte. It will
  return -1 if the end of file has been reached

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public class CTEC1641_Lecture4_ReadBytes
public static void main(String arguments)
try FileInputStream TheFile new
FileInputStream("TheGoods.dat")
boolean TheEndOfFile false int Counter1
0 while (!TheEndOfFile) int input
TheFile.read() System.out.print(input "
") if (input -1) TheEndOfFile
true else Counter1 Counter1
1 TheFile.close() System.out.println(
"\nBytpes read " Counter1) catch
(IOException e) System.out.println("Error "
e.toString())
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File Output Stream - Byte

• Often there is the need to write bytes to a file.
  This is done using FileOutputString(String).
• CAUTION If there is a file that already exists
  with the same name. It will be overwritten and
  the contents lost.
• How to check for existing file? Use
  FileOutputString(String,Boolean).
• String gives the name of the file
• If Boolean is true it will append data

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import java.io. public class
CTEC1641_Lecture4_WriteBytes public static
void main(String arguments) int SomeData
1, 2, 3, 4, 5, 6, 7, 8, 9, 10 int
SomeMoreData 55, 56, 34, 45, 56, 61, 71, 81,
82, 84 //Lets try to write a file try
FileOutputStream TheFile new
FileOutputStream("APileOfStuff.dat") for (int
i 0 i lt SomeData.length i)
TheFile.write(SomeDatai)
TheFile.close() catch (IOException e)
System.out.println("Error "
e.toString()) //Nows lets write a file,
but check fist try FileOutputStream
TheFile new FileOutputStream("APileOfStuff.dat",
true) for (int i 0 i lt SomeMoreData.length
i) TheFile.write(SomeMoreDatai)
TheFile.close() catch (IOException e)
System.out.println("Error "
e.toString())
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Buffered Input Streams

• Buffered input streams allow you to store data
  that has not been handled yet. When a program
  needs the data, it goes to the buffer first. This
  can be more efficient due to the time delay of
  reading in information from external devices.
  (i.e. CD-ROM require time to spin-up) Often it
  is more efficient to read a block of information
  first then process it.

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Buffered Input Streams

• Buffered input streams are initialized using the
  following code
• BufferedInputStream(InputStream) Creates a
  buffered input steam for the specified InputSteam
  object.
• BufferedInputStream(InputStream, int)- Creates
  the specified InputStream with a buffer of int
  size
• Use the read() method which returns an integer
  value of 0 to 255 (byte)
• End of stream is represented by a -1

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Buffered Byte Input Streams cont

• Read(byte, int, int) method is also available
  which can load the steam into an array

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Buffered Byte Output Stream

• A buffered output stream is created using the
  following constructors
• BufferedOutputStream(OutputStream) Creates a
  buffered output steam for the specified
  OutputStream object
• BufferedOutputStream(OutputStream, int) Creates
  the specified OutputStream buffered stream with
  buffere of int size

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Buffered Byte Output Stream cont

• The output streams write(int) method can be used
  to send a single byte to the stream and the
  write(byte, int, int) method writes bytes from
  the specified byte array.
• NOTE Although the write method takes integers as
  input, the number cannot be over 255. If it is,
  it will be stored as the remained of the number
  divided by 256.

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Buffer Output Byte Stream cont

• When data is directed to a stream, it is not
  output to its destination (i.e. file) until the
  buffer is filled, or called by the flush()
  method. close() will also invoke this.

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import java.io. public class
CTEC1641_Lecture4_WriteBuffBytes public static
void main(String arguments) int SomeData
1, 2, 3, 4, 5, 6, 7, 8, 9, 10 int
SomeMoreData 55, 56, 34, 45, 56, 61, 71, 81,
82, 84 //Lets try to write a file try
FileOutputStream TheFile new
FileOutputStream("APileOfStuff.dat") BufferedO
utputStream buff new BufferedOutputStream(TheFil
e) for (int i 0 i lt SomeData.length i)
buff.write(SomeDatai) buff.close(
) catch (IOException e) System.out.print
ln("Error " e.toString()) //Nows
lets write a file, but check fist try
FileOutputStream TheFile new
FileOutputStream("APileOfStuff.dat",true) Buff
eredOutputStream buff new BufferedOutputStream(T
heFile) for (int i 0 i lt
SomeMoreData.length i) buff.write(SomeMor
eDatai) buff.close() catch
(IOException e) System.out.println("Error "
e.toString())
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Data Streams

• Often we need to work with data that is not bytes
  or characters. The following filters can be used
  allow the programmer to work directly with the
  stream, rather than managing the conversion
  themselves.
• DataInputStream data new DataInputStream(buff)
  
• Each input method returns the primitive data type
  indicated by the method name.

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Data Streams cont

• readBoolean(), writeBoolean(boolean)
• readByte(), writeByte(integer)
• readDouble(), writeDouble(double)
• readFloat() writeFloat(float)
• readInt(), writeInt(int)
• readLong(), writeLong(long)
• readShout(), writeShort(int)

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import java.io. public class
CTEC1641_Lecture4_WriteBuffBytesFilter public
static void main(String arguments) int
SomeData 97, 98, 99, 100, 114, 114, 123, 32,
221, 10 //Lets try to write a file try
FileOutputStream TheFile new
FileOutputStream("APileOfStuff.dat") Bu
fferedOutputStream buff new BufferedOutpu
tStream(TheFile) DataOutputStream data new
DataOutputStream(buff) for (int i 0 i lt
SomeData.length i) data.writeLong(SomeDat
ai) buff.close() catch
(IOException e) System.out.println("Error "
e.toString())
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File Input Character Streams

• Character streams work with both ASCII text and
  also Unicode
• Use Reader and Writer to read and write files
  respectively.
• Assocated with file using
• FileReader ATextFile new FileReader(blah.txt)
  

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File Input Character Streams cont

• Read method is overloaded
• read() returns the next character as an integer
• read(char, int, int) reads character into the
  specified array with indicated starting point and
  number of characters read
• As with byte streams they will return a -1 if
  there is nothing read.

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import java.io. class CTEC1641_Lecture4_FileRea
derExample public static void main(String
args) try FileReader ATextFile
new
FileReader("ExampleTextFile.txt")
int TheByte0 while (TheByte ! -1)
TheByte ATextFile.read() if (TheByte
! -1) System.out.print( (char)TheByte
) System.out.println("") catch
(IOException e) System.out.println("Error
with the file")
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TextFile Output Character Streams

• In order to write text files use the FileWriter
  class.
• FileWriter letters new FileWriter("TheFileToWri
  te.txt")
• Two overloaded FileWriter methods for writing
• write (int) - This writes out a single character
• write (char, int, int) Writes out a specified
  amount of characters from an array.
• write (String, int, int) Writes a character
  from a given string

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import java.io. public class
CTEC1641_Lecture4_WriteTextFile public
static void main(String arguments) try
FileWriter letters new FileWriter("T
heFileToWrite.txt") for (int i 65 i lt 91
i) letters.write( (char)i
) letters.close() catch (IOException e)
System.out.println("Error "
e.toString())
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Text Files Buffered Reader/Writer

• BufferedWriter can be used to write a buffered
  character stream.
• BufferedWriter(Writer)
• BufferedWriter(Writer, int)
• The Writer argument can be any of the character
  output stream classes, such as FileWriter. The
  option second argument is an integer indicating
  the size of the buffer to use.

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Files - Misc

• File represents a file or folder reference.
• Uses the following constructors
• File(String) Creates a File object with the
  specified folder no filename is indicated for
  this refers only to a file folder.
• File(String, String) Creates a File object with
  the specified folder path and the specified name.
• File(File, String) Creates a File object with
  its path represented by the specified File and
  its name indicated by the specified String

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File Objects

• There are many methods
• Exists() method returns a Boolean value
  indicating whether the file exists
• For a given file object, you can use the length()
  method to return a long integer indicating the
  size of the file in bytes.
• The renameTo(File) method renames the file to the
  name specified by the File argument. A Boolean
  value is returned, indicating whether the
  operating was successful.

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File cont

• The delete() or deleteOnExit() method should be
  called to delete a file or folder.
• delete() does it right away. Returns a boolean
  indicating success or failure.
• deleteOnExit() waits for the termination of the
  program
• getName() and getPath() methods return strings
  containing the name and path of the file.

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File cont

• mkdir() method can be used to create the folder
  specified. It returns a Boolean value indicating
  success or failure.
• delete() can also be used on folders
• isDirectory() method returns the Boolean value
  true when the File object is a folder all its
  files and subfolders

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File cont

• listFiles() methods returns an array of File
  object representing the contents of the file, all
  of its files and subfolders.
• The file methods will throw a SecurityException
  if the program doesnt have the security to
  perform the file operation.

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Exercise

• Using the program that you developed at the start
  of class, add a method that reads in a file
  containing values that represents changes to the
  vehicles speed. Use these values to change the
  speed of the vehicle each time a new value is
  read in. When the end of the file has been
  reached, the vehicles speed is reduced to zero.