Binary%20Files%20

1
Cosc 1P02

• Binary Files Persistent Objects

For myself, I am an optimist--it does not seem
to be much use being anything else. Winston
Churchill
2
Files

• collections of data stored on external media
• disk, tape, CD-ROM, DVD
• file management (O/S)
• external file name
• processing
• open
• internal file name
• file reference
• process
• close
• stream I/O vs record I/O

3
Record I/O

• field
• indivisible
• record
• database
• key
• natural key
• assigned key
• I/O of entire record from /to binary file
• record/structure variables
• object-oriented I/O

4
Record Output

• object I/O to binary streams only
• output
• constructor opens file
• external file name
• writeObject()
• subtype
• upcasting to Object
• always valid
• class must implement Serializable
• security
• interfaces

5
E.g. Create an Employee File

• Employee records
• Employee class from Example 7.2
• Serializable
• Class serial identification number
• SUID explicitly stated.
• If not explicitly state
• Created at compile time as a computed hash of
  various class elements class name, implemented
  interfaces, declared nonstatic, nontransient
  fields, declared nonprivate methods, and so on.
• data from a text file
• Read text file until EOF
• reads text record using Employee constructor
• writes Employee object using writeObject

6
Record Input

• readObject()
• must downcast to expected type
• not a conversion
• ClassCastException
• Matches serial number (SUID) of object to
  objects class specification
• Security
• Class Versioning.

7
E.g. List Employee File

• not a text file so cannot view in text editor
• number of pieces of work
• report generation to EOF
• no use of Employee constructor
• Employees are not new
• persistent objects
• serialization
• same class file
• can recompile Employee class
• If explicit serialVersionUID is used
• PayRoll with persistent objects

8
PayRoll Employee file.
1111 12.50 10000.00 2300.00 2222 5.50 4400.00 0.0
0 3333 7.50 3000.00 0.00 4444 45.00 36000.00 8280
.00
9
(No Transcript)
10
Employee Class

• package Example_7_2
• import java.io.
• import BasicIO.
• public class Employee implements Serializable
• private static final long serialVersionUID
  123456L
• private String empNum // employee number
• private double rate // pay rate
• private double ytdGross // year-to-date
  gross pay
• private double ytdTax // year-to-date
  taxes paid
• / The constructor creates a new employee
  reading the employee
• data from a file.
• _at_param from data file for employee data.
  /

11
EmployeeCreate
package Example_7_2 import
BasicIO. public class EmpCreate
private ASCIIDataFile in //
employee data file private BinaryOutputFile
out // new employee data file
public EmpCreate () Employee
aE in new ASCIIDataFile() out
new BinaryOutputFile() while
(true) aE new Employee(in) if
(in.isEOF()) break out.writeObject(aE)
in.close() out.close()
// construtor public
static void main ( String args ) new
EmpCreate()

12
Employee List

• public class EmployeeList
• private BinaryDataFile empFile //
  employee data file
• private ASCIIDisplayer out
• public EmployeeList ( )
• empFile new BinaryDataFile()
• out new ASCIIDisplayer()
• // construtor
• public void run ( )
• Employee anEmployee // current employee
• while (true)
• anEmployee (Employee)empFile.readObject()
• if (empFile.isEOF()) break
• this.writeDetail(anEmployee)
• empFile.close()

13
PayRoll

• private void runPayroll ( )
• int numEmp // number of
  employees
• Employee anEmployee // current
  employee
• double hours // hours worked
• double pay // weekly pay
• int button // button pressed
• numEmp 0
• while ( true )
• anEmployee (Employee)empFile.readObj
  ect()
• if ( empFile.isEOF()
  !empFile.successful()) break
• payForm.clearAll()
• fillForm(anEmployee)
• button payForm.accept("Pay","Next")
  
• if ( button 0 )
• hours payForm.readDouble("hours"
  )
• pay anEmployee.calculatePay(hour
  s)
• fillForm(anEmployee)

14
The End