1. Intro to Programming & Algorithm Design
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Intro to Programming & Algorithm Design
Data Files
Assg
This presentation can be viewed on line in a file named: ch09.IntrotoProg.Files.ppt
Copyright 2003 by Janson Industries

2. Objectives Explain Show how to use files in Java Advantages of files
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Objectives
Explain
Advantages of files
How to process files
Show how to use files in Java

3. File Everything on a computer is stored in files Images Documents
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File
Everything on a computer is stored in files
Images
Documents
Web pages
Spreadsheet
Flowcharts
Java source code
Java bytecode

4. Data File We are talking about data files
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Data File
We are talking about data files
Inventory data
Customer data
Sales data
Kind of like an array but more permanent
When pgm stops data still exists

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File Advantages
Instead of entering data every time a pgm is run, user can enter once and pgm can save to a file
Data can then be accessed at a later time
This is how apps remember info
Browser favorities
Amazon purchase history
Video game high scores

6. Data Files Are stored on secondary storage
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Data Files
Are stored on secondary storage
Hard drive
Flash drive
Cloud drive
A program can put data into a file (write to the file) or retrieve a copy of the data from the file (read the file)

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Files
Programs read files just like they read data from the command line
Can read the entire line
Can read one word
i.e. All the text up to the next space
Programs write to files just like they write to the console
With a carriage return
Without carriage return

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Files
When writing, some languages will overwrite any existing data in a file
Others let you append data
Before a file can be written to or read from, it must be opened
Any data written to a file will be saved when the file is closed by the progam
Actually closing forces any data still in the buffer into the file.

9. Files In pseudocode you must declare a program file name
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Files
In pseudocode you must declare a program file name
At the same time the file must also be defined as input or output
Lastly, the program file name has to be associated with the file's physical name

10. Files Windows file's physical names have a prefix and a suffix
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Files
Windows file's physical names have a prefix and a suffix
Prefix can have many parts (separated by periods) but the suffix indicates the type of info in the file
Dear.John.docx
My.First.Pgm.java
My.Latest.Greatest.Selfie.jpeg

11. Writing to Files Declare the file as an output file
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Writing to Files
Declare the file as an output file
The program file name and the file's physical name are tied together in the open statement
Declare OutputFile customerFile
Open customerFile "Customer.dat"
Write customerFile "Joe Customer"
Write customerFile "1 Main St."
Write customerFile "Enid, OK "
Close customerFile

12. Results in the 3 variables holding the file data
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Reading Files
Declare the program file name as input
Associate it with the physical file name
Read the file
Declare String custName, custStreet,
custCSZ
Declare InputFile customerFile
Open customerFile "Customer.dat"
Read customerFile custName
Read customerFile custStreet
Read customerFile custCSZ
Close customerFile
Results in the 3 variables holding the file data

13. Appending to Files In the declare, identify the mode as AppendMode
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Appending to Files
In the declare, identify the mode as AppendMode
So, running the following
Results in
Declare OutputFile AppendMode customerFile
Open customerFile "Customer.dat"
Write customerFile "Mary Buyer"
Write customerFile "2 Oak St
Write customerFile "Muncie, IN 54545"
Close customerFile

14. Using Loops to Process Files
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Using Loops to Process Files
Like arrays, loops very useful for accessing data in files
Unlike arrays, files can have variable amounts of data
No length variable for files
Most file systems have a way to determine if the end of the file has been reached

15. Using Loops to Process Files
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Using Loops to Process Files
In pseudocode, use the eof (end of file) function
eof(customerFile) will return a true if the last record/line has been read
Can use eof in a while loop to process all the data in a file

16. Using Loops to Process Files
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Using Loops to Process Files
Assuming Customer.dat has the following info

17. Using Loops to Process Files
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Using Loops to Process Files
To display a mailing list like this:
Joe Customer
1 Main St.
Enid, OK
Mary Buyer
2 Oak St.
Muncie, IN 54545
Terry Smith
3 Pine Ave.
Palatka, FL 32273
Pat Jones
4 Lake Dr.
Erie, PA

18. Using Loops to Process Files
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Using Loops to Process Files
Module main()
Declare Integer ctr
Declare String tempVariable
Declare InputFile customerFile
Open customerFile "Customer.dat"
While NOT eof(customerFile)
For ctr = 1 to 3
Read customerFile tempVariable
Display tempVariable
End For
Display " "
End While
Close customerFile
End Module

19. Raptor Flowgorithm cannot process files So new tool - Raptor
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Raptor
Flowgorithm cannot process files
So new tool - Raptor
Like Flowgorithm, can execute the flowchart
Several differences between Flowgorithm and Raptor

20. Raptor No declare function Only global variables
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Raptor
No declare function
Must specify Declares as commments
Only global variables
No passing variables between modules
No distinction between modules and functions
Input function also has output function for prompt text

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Raptor
For example, here’s a Raptor FC that adds two numbers

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Raptor
When executed result is:

24. Scroll down

25. Click drop down button, select Save As, then specify your thumb drive
Click Save

26. Double click to start install

29. Specify thumb drive location (this way you can run from any computer)

32. To run, double click raptor.exe

33. Or from the All Apps menu, select Raptor

34. This is where the flowchart is defined
Output shown here

35. To add a symbol, click to select…
Raptor
To add a symbol, click to select…

36. … then click in flowchart where to put the symbol
Raptor
… then click in flowchart where to put the symbol
You can also drag/drop

37. To edit symbol (add function) click symbol…
Raptor
To edit symbol (add function) click symbol…

38. Then click Edit and Edit Selection
Raptor
Then click Edit and Edit Selection

39. Enter statement(s), click done
Raptor
Enter statement(s), click done

40. To run, click the Execute to Completion button
Raptor
To run, click the Execute to Completion button

41. Output displayed in Console
Raptor
Output displayed in Console

42. Raptor Raptor has two symbols for I/O
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Raptor
Raptor has two symbols for I/O
One for input
One for output
The input symbol actually does an output first
A text prompt is displayed
Then the input is done

43. Can also just double click the symbol to edit
Raptor
Can also just double click the symbol to edit

44. Enter prompt text, variable to hold info, click Done
Raptor
Enter prompt text, variable to hold info, click Done

45. Notice Raptor uses + not & to concatenate
Added an output symbol
Notice Raptor uses + not & to concatenate

46. As each symbol is executed, it’s outlined in green
Raptor
As each symbol is executed, it’s outlined in green

47. Raptor
When input symbol reached, program execution halts and a window is displayed with the prompt text and an input field

48. User should enter the input and click OK
Raptor
User should enter the input and click OK

49. Raptor Program finishes executing and results displayed in console
To insert a comment, right click a symbol and select Comment

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Files in Raptor
To read, use the Input function but must first identify the file as the source of the input
I.e. not the keyboard/console
Done by calling the Redirect_Input function
Redirect_Input("E:/Customer.dat")
To write to a file use the Redirect_Output function

51. Using File Loops in Raptor
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Using File Loops in Raptor
Raptor has an End_Of_Input function that is used to control a loop
To close a file, set the redirect to false
Redirect_Input(false)

52. Using File Loops in Raptor
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Using File Loops in Raptor
EOF loop to read all records
Loop to read the three records for each customer

53. Using File Loops in Raptor
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Reads and displays a record
Blank line separating each customers data
Close the file

54. Using File Loops in Raptor
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Using File Loops in Raptor
Results

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Files in Java
To read, still use a Scanner and its next(), nextLine, nextDouble, etc. methods
Need to tie the scanner to the file
Done when creating the Scanner
Need to import java.io.File;
Scanner customerFile = new Scanner(new File("E:/Customer.dat"));

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Files in Java
If the file doesn't exist, creating the scanner will cause a File Not Found Exception
Two ways to handle
Put the following code in the header of the method
And import java.io.IOException;
public static void main(String[] args) throws IOException {

57. Files in Java Or you can enclose the statement as follows
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Files in Java
Or you can enclose the statement as follows
And import java.io.FileNotFoundException;
try {
customerFile = new Scanner(new File("E:/Customer.dat"));
} catch (FileNotFoundException e) {
e.printStackTrace(); }

58. Using File Loops in Java
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Using File Loops in Java
The Scanner has a method called hasNext
Will return true if there is more data
To close a file, use the Scanner's close method
customerFile.close();

59. Using File Loops in Java
import java.io.File;
import java.io.IOException;
import java.util.Scanner;
public class FileLoop {
public static void main(String[] args) throws IOException {
//Declare variables
int ctr; String tempVariable = new String();
//Declare objects and variables needed to read the file
Scanner customerFile = new Scanner(new
File("E:/Customer.dat"));
while(customerFile.hasNext()) {
for(ctr = 1; ctr <4; ctr++) {
//Reads and displays one record from the file
tempVariable = customerFile.nextLine();
System.out.println(tempVariable); }
//Blank line for readablity
System.out.println("");
//Close the file
customerFile.close();
} }
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Using File Loops in Java

60. Using File Loops in Java
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Using File Loops in Java

61. Modifying Files Text files not always easy to add to or modify
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Modifying Files
Text files not always easy to add to or modify
That's why there are Databases
Some languages allow you to append to the file but some don't
But no language has an easy way to modify

62. Modifying Files To add when language doesn't allow adding, have to:
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Modifying Files
To add when language doesn't allow adding, have to:
Read all the records from the file
Write them to a temp file
Get the new data and write it to the temp file
Then read all the records from the temp file
Write them to the original file
I.e. write over what was in the original file

63. Modifying Files - Adding
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Modifying Files - Adding
Old
Data
Old
Data
Customer.dat
AddPgm
TempFile.dat
New
Data
New
Data
AddPgm
User
Old and New Data
Old and New Data
AddPgm

64. 4/20/2018
Adding a Record
Fortunately, Java allows appending so we won't have to mess with the temporary file when adding
But Raptor doesn't!!
Also, we should check the file and make sure that a record doesn't already exist for the "new" data
Have to search the entire file before adding a record

65. Modifying a Record User specifies record to modify
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Modifying a Record
User specifies record to modify
Read and write all the records from original file to temp until the record to modify is read
Prompt the user with the old data
Get new data and write it to temp
Read rest of original records and write them to temp
Copy temp back to original

66. Modifying a Record Data To Modify AddPgm User Data Records Up to the
one to modify
Data
Records
Up to the
one to modify
Customer.dat
AddPgm
TempFile.dat
Old Data
New Data
AddPgm
User
New Data

67. Modifying a Record Rest of Data Rest of Data Customer.dat AddPgm
TempFile.dat
All
Data
All
Data
Customer.dat
AddPgm
TempFile.dat

68. 4/20/2018
Modifying Files
Will design a program to allow users to add, modify or display a customer's information
If user wants to add a customer, will check that info for that customer does not already exist
If info does exist, will not allow user to add

69. Modifying Files Module main() Declare String option = ""
While option NOT equal “4”
Display "What would you like to do? Enter:"
Display "1 to add a customer"
Display "2 to modify a customer"
Display "3 to display a customer"
Display "4 to end the pgm"
Input option
If option = "1" Then
addRecord()
Else If option = "2" Then
modifyRecord()
Else If option = "3" Then
displayRecord()
End If
End While
End Module
Modifying Files
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70. Modifying Files Module addRecord() Declare String custToAdd
Declare String custNameInFile
Declare String tempVariable
Declare Boolean recordExists = false
custToAdd = getCustomerName()
Declare InputFile customerFile
Open customerFile "Customer.dat"
While NOT eof(customerFile) AND recordExists = false
Read customerFile custNameInFile
If custNameInFile = custToAdd Then
recordExists = true
Else For ctr = 1 to 2
Read customerFile tempVariable
End For
End If
End While
Close customerFile
Modifying Files
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71. Modifying Files If recordExists = true Then
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If recordExists = true Then
Display "Sorry there is already a record for customer " +
custToAdd
Else
Declare OutputFile AppendMode customerFileOut
Open customerFileOut "Customer.dat"
Write customerFileOut custToAdd
Display "What is the customers street address"
Input tempVariable
Write customerFileOut tempVariable
Display "What is the customers city, state and zip"
Display "Customer " + custToAdd + " added"
Close customerFileOut
End If
End Module

72. Read till record to change found
Module modifyRecord()
Declare String custToMod
Declare String custNameInFile
Declare String tempVariable
Declare Boolean recordExists = false
custToMod = getCustomerName()
Declare OutputFile tempFile
Open tempFile "TempFile.dat"
Declare InputFile customerFile
Open customerFile "Customer.dat"
While NOT eof(customerFile) AND recordExists = false
Read customerFile custNameInFile
Write tempFile custNameInFile
If custNameInFile = custToMod Then
recordExists = true
Else For ctr = 1 to 2
Read customerFile tempVariable
Write tempFile tempVariable
End For
End If
End While
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Modifying Files
Read till record to change found

73. If record found get new info and write it to temFile
Modifying Files
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If record not found
If recordExists = false Then
Display "Sorry there is no record for customer " + custToMod
Close customerFile
Else
Read customerFile tempVariable
Display "This is the customers current street address "
Display tempVariable
Display "What is the customers new street address"
Input tempVariable
Write tempFile tempVariable
Display "This is the customers current city, state and zip"
Display "What is the customers new city, state and zip"
Display "Customer " + custToMod + " changed"
End If
If record found get new info and write it to temFile

74. Modifying Files While NOT eof(customerFile)
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While NOT eof(customerFile)
Read customerFile tempVariable
Write tempFile tempVariable
End While
Close customerFile
Close tempFile
Declare InputFile tempFileIn
Open tempFileIn "TempFile.dat"
Declare OutputFile customerFileOut
Open customerFileOut "Customer.dat"
While NOT eof(tempFileIn)
Read tempFileIn tempVariable
Write customerFileOut tempVariable
Close customerFileOut
Close tempFileIn
End Module
Write rest of customer records to tempFile
Write all records to Customer from tempFile

75. Read till record to display found When found display the 3 records
Module displayRecord()
Declare String custToDisp
Declare String custNameInFile
Declare String tempVariable
Declare Boolean recordExists = false
custToDisp = getCustomerName()
Declare InputFile customerFile
Open customerFile "Customer.dat"
While NOT eof(customerFile) AND recordExists = false
Read customerFile custNameInFile
If custNameInFile = custToDisp Then
recordExists = true
Display custNameInFile
For ctr = 1 to 2
Read customerFile tempVariable
Display tempVariable
End For
Display " "
End If
End While
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Modifying Files
Read till record to display found
When found display the 3 records

76. Modifying Files If recordExists = false Then
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Modifying Files
If recordExists = false Then
Display "Sorry there is no customer " + custToDisp
End If
Close customerFile
End Module
Function String getCustomerName()
String custName
Display "What is the customers name"
Input custName
Return custName
End Function

77. Modifying Files Raptor
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Modifying Files Raptor
Raptor has a problem with accepting numeric characters as strings, will make option an Integer
Can't append, so will have to work with temp file to do an Add
This means opening the TempFile when we open Customer
As we search to see if customer already exists, write each record to temp

78. Modifying Files Raptor
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main method
Modifying Files Raptor
Display options and input option
Call correct function

79. Modifying Files Raptor
addRecord method
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Modifying Files Raptor
Loop checking if customer already exists

80. Modifying Files Raptor
addRecord method
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Modifying Files Raptor
Checking customer name
No match: write name and next two records to the temp file
Close customer file

81. Modifying Files Raptor
addRecord method
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Modifying Files Raptor
No match: write name to temp prompt user to supply data, read, write to temp file
Match: display msg no add done
Close temp, then open temp as input and customer as output

82. Modifying Files Raptor
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addRecord method
Modifying Files Raptor
Write all records from temp to customer
Close files and display user msg

83. Modifying Files Raptor
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Modifying Files Raptor
In Raptor, when you are writing to a file, can't display info in console
Well… you could but this means the redirect must be set to false and the next write will overwrite the file
So in modifyRecord:
Won't prompt with current data
Must get all the new data before redirecting
Will need two more variables to hold the data

84. Modifying Files Raptor
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Modifying Files Raptor
Alternatively, we could:
Read the entire file looking for record
Retrieve the data
Then read the entire file again and write to the temp file, etc.
Would mean a extra read of the entire file…

85. Loop to find record to be changed
modifyRecord method
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Modifying Files
Get new info
Set up files
Loop to find record to be changed

86. Modifying Files Raptor
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modifyRecord method
Check if record found
Modifying Files Raptor
No match: write cust name and next two records to temp

87. Modifying Files Raptor
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Modifying Files Raptor
Match: write new customer data
Match: skip rest of old customer data
No match: no change
Match: write rest of data from customer to temp 87

88. Modifying Files Raptor
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modifyRecord method
Close files
Modifying Files Raptor
Re-open so temp is input and customer is output
Write all data from temp to customer

89. Modifying Files Raptor
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modifyRecord method
Modifying Files Raptor
Close files
Display user msg

90. Displaying Files Raptor
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displayRecord method
Displaying Files Raptor
Loop to search for record to display

91. Displaying Files Raptor
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If record found display the name…
Displaying Files Raptor
displayRecord method
…get and display next 2 records with rest of data

92. Displaying Files Raptor
displayRecord method
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Displaying Files Raptor
Display blank line
If record was not found display user msg
Close file

93. Modifying Files Raptor
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Modifying Files Raptor
getCustomerName method

94. Modifying Files - Raptor
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Modifying Files - Raptor
Given this data

95. Modifying Files Raptor
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Modifying Files Raptor
Running the flowchart results in:

96. Modifying Files Raptor
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Modifying Files Raptor
Specifying new customer info:

97. Modifying Files Raptor
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Modifying Files Raptor
Changing customer info:

98. Modifying Files Raptor
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Modifying Files Raptor

99. Modifying Files Raptor
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Modifying Files Raptor
And this is the data at the end

100. Modifying Files Java To write to a file you use a PrintWriter
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Modifying Files Java
To write to a file you use a PrintWriter
Specify the file name and location when creating the PrintWriter object
Like you did with the Scanner
Have to enclose in try/catch or specify throws IOException in method header
PrintWriter tempFile = null;
tempFile = new PrintWriter("E:/TempFile.dat");

101. Modifying Files Java To append to a file you also use a FileWriter
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Modifying Files Java
To append to a file you also use a FileWriter
But you create a FileWriter object and specify the file name and the value true
PrintWriter customerFileOut = null;
customerFileOut =
new PrintWriter(new FileWriter("E:/Customer.dat", true));

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Modifying Files Java
To write you use the PrintWriters print or println methods
println writes data to a new line in the file
print writes to the same line
customerFileOut.println("Frank Smith");
String custName = "Joe Blow"
customerFileOut.print(custName);
Frank SmithJoe Blow

103. Modifying Files in Java
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import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;
public class FileMod {
static Scanner keyboard = new Scanner(System.in);
public static void main(String[] args) {
String option = "";
// Display menu of options
while (!option.equals("4")) {
System.out.println("What would you like to do? Enter:");
System.out.println("1 to add a customer");
System.out.println("2 to modify a customer");
System.out.println("3 to display a customer");
System.out.println("4 to end the pgm");
option = keyboard.nextLine();
main method

104. Modifying Files in Java
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// Invoke correct method based on option selected
if (option.equals("1")) {
addRecord();
} else {
if (option.equals("2")) {
modifyRecord();
if (option.equals("3")) {
displayRecord(); }
public static void addRecord() {
// Variables to hold file data
String custToAdd, custNameInFile, tempVariable;
boolean recordExists = false;
// Variables for reading and writing to the customer file
Scanner customerFile = null;
PrintWriter customerFileOut = null;
Modifying Files in Java
addRecord method

105. Modifying Files in Java
// Retrieve the customer name to add
custToAdd = getCustomerName();
// Create the scanner object to read the customer file
try {
customerFile = new Scanner(new File("E:/Customer.dat"));
} catch (FileNotFoundException e) {
e.printStackTrace(); }
// Read every record and compare every third record
//with the new name
while (customerFile.hasNext() && recordExists == false) {
custNameInFile = customerFile.nextLine();
if (custNameInFile.equals(custToAdd)) {
recordExists = true;
} else {
for (int ctr = 1; ctr < 3; ctr++) {
tempVariable = customerFile.nextLine();
customerFile.close();
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Modifying Files in Java

106. End of addRecord method
// If customer name is already in file, don't add
if (recordExists == true) {
System.out.println("Sorry there is already a record for customer " + custToAdd);
} else {
// Create PrintWriter object to append to customer file
try {
customerFileOut = new PrintWriter(new FileWriter(
"E:/Customer.dat", true));
} catch (IOException e) {
e.printStackTrace();}
// Append the new name, address and CSZ to the customer file
customerFileOut.println(custToAdd);
System.out.println("What is the customers street address");
tempVariable = keyboard.nextLine();
customerFileOut.println(tempVariable);
System.out.println("What is the customers city, state and zip");
System.out.println("Customer " + custToAdd + " added");
customerFileOut.close(); }
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End of addRecord method

107. modifyRecord method public static void modifyRecord() {
String custToMod, custNameInFile, tempVariable;
boolean recordExists = false;
custToMod = getCustomerName();
// Variables and objects for reading and writing
// to the customer and temp files
Scanner tempFileIn = null;
Scanner customerFile = null;
PrintWriter tempFile = null;
PrintWriter customerFileOut = null;
try {
customerFile = new Scanner(new File("E:/Customer.dat"));
tempFile = new PrintWriter("E:/TempFile.dat");
} catch (FileNotFoundException e) {
e.printStackTrace(); }
// Read the customer file and write the info to the temp // file until the customer to modify is found
while (customerFile.hasNext() && recordExists == false) {
custNameInFile = customerFile.nextLine();
tempFile.println(custNameInFile);
if (custNameInFile.equals(custToMod)) {
recordExists = true;
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modifyRecord method

108. modifyRecord method } else { for (int ctr = 1; ctr < 3; ctr++) {
tempVariable = customerFile.nextLine();
tempFile.println(tempVariable); }
// If the customer name not in file, don't allow change
if (recordExists == false) {
System.out.println("Sorry there is no record for customer " + custToMod);
customerFile.close();
// Get the current customer info and display it
// Read the new info and write it to the temp file
System.out.println("This is the customers current street address ");
System.out.println(tempVariable);
System.out.println("What is the customers new street address ");
tempVariable = keyboard.nextLine();
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modifyRecord method

109. modifyRecord method tempVariable = customerFile.nextLine();
System.out.println("This is the customers current city, state and zip ");
System.out.println(tempVariable);
System.out.println("What is the customers new city, state and zip ");
tempVariable = keyboard.nextLine();
tempFile.println(tempVariable);
System.out.println("Customer " + custToMod + " changed");
// Write the rest of the customer records to the temp file
while (customerFile.hasNext()) { }
// Close the files then create new objects to
// read the temp file and write to the customer file
customerFile.close();
tempFile.close();
try {
tempFileIn = new Scanner(new File("E:/TempFile.dat"));
customerFileOut = new PrintWriter("E:/Customer.dat");
} catch (FileNotFoundException e) {
e.printStackTrace();}
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modifyRecord method

110. End modifyRecord method
// Copy all the temp file records to the customer file
while (tempFileIn.hasNext()) {
tempVariable = tempFileIn.nextLine(); customerFileOut.println(tempVariable); }
customerFileOut.close();
tempFileIn.close();
// Display a particular customers record.
// Uses same logic as FileLoop.
public static void displayRecord() {
String custToDisp, custNameInFile, tempVariable;
boolean recordExists = false;
Scanner customerFile = null;
custToDisp = getCustomerName();
try {
customerFile = new Scanner(new File("E:/Customer.dat"));
} catch (FileNotFoundException e) {
e.printStackTrace(); }
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End modifyRecord method
displayRecord method

111. End displayRecord method getCustomerName method
while (customerFile.hasNext() && recordExists == false) {
custNameInFile = customerFile.nextLine();
if (custNameInFile.equals(custToDisp)) {
recordExists = true;
System.out.println(custNameInFile);
for (int ctr = 1; ctr < 3; ctr++) {
tempVariable = customerFile.nextLine();
System.out.println(tempVariable); }
System.out.println(""); }
if (recordExists == false) {
System.out.println("Sorry there is no customer " + custToDisp); }
customerFile.close();
public static String getCustomerName() {
String custName;
System.out.println("What is the customers name");
custName = keyboard.nextLine();
return custName;
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End displayRecord method
getCustomerName method

112. 4/20/2018
Modifying Files - Java
Given this data

113. Display newly added customer info
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Modifying Files - Java
Choose add
Add new customer
Display newly added customer info

114. Display changed customer info
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Modifying Files - Java
Choose modify
Change some of the data
Display changed customer info

115. Modifying Files - Java Test that all checks work
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Modifying Files - Java
Test that all checks work
Try to add an already existing customer
Try to change and display a non-existing customer

116. 4/20/2018
Modifying Files - Java
And this is the data at the end

117. Processing File Data Files can hold both text and numbers
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Processing File Data
Files can hold both text and numbers
Instead of using parallel arrays can use files to hold different types of info

118. Processing Data
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And a language like Java lets you read individual values not just the whole record
next() gets all text up to the next space
nextInt() gets all text up to the next space and converts it to an integer
nextDouble() gets all text up to the next space and converts it to a double
All of these do not advance the cursor to the next line!

119. Processing Data Not nitpicking! If file had the following budget data
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Not nitpicking! If file had the following budget data
And you tried to process with these statements
Rent
500
Car
280
Utilities
175
While (not eof)
name = infile.nextLine()
amount = infile.nextDouble()
End While

120. Processing Data
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There would be an exception the second time nextDouble executed
WHAAAAAAAT!!
Must show where cursor is after each statement executed to understand
First nextLine() reads "Rent" and places cursor at the beginning of the second line in the file

121. Cursor after first read Cursor after second read
Processing Data
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When nextDouble executed 500 read and cursor placed at end after the second 0
When the second nextLine executed it reads the rest of the second line
A big fat null
Rent
500
Car
280
Utilities
175
Cursor after first read
Cursor after second read

122. Processing Data And moves cursor to beginning of third line
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And moves cursor to beginning of third line
Now when second nextDouble executed
InputMismatchException
Tries to convert "Car" into a double
Rent
500
Car
280
Utilities
175
Cursor after 3rd read
(2nd nextLine)

123. Processing Data Solution:
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Processing Data
Solution:
Execute another nextLine after the nextDouble
Forces the cursor to the line after the line with the double value
While (not eof)
name = infile.nextLine()
amount = infile.nextDouble()
infile.nextLine()
End While

124. 4/20/2018
Processing Data
When using files like this, there is generally a file specification document which
Identifies each field of data with a
Name
Location within the file
Size (optional)
Data type

125. Processing Data So we could have stored the customer data like this
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Processing Data
So we could have stored the customer data like this
The file specification would look something like this…

126. Processing Data File Name: customer.dat
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Processing Data
File Name: customer.dat
Description: contains the name and address of each customer
Field Description Data Type
Customer first name String
Customer last name String
Street number String
Street name String
Street type String
City String
State String
Zip code String

127. Processing Data Storing data this way could cause problems
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Processing Data
Storing data this way could cause problems
What if street name is comprised of multiple words
23 Pond View Dr.
14 Puppy Dog Tr.
2300 Martin Luther King Hwy
How do you know how many reads to do?
Could add a new field that has the street name length (number of words)

128. Processing Data Uh-oh what about city now?
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Processing Data
Joe Customer 1 1 Main St Enid, OK
Mary Buyer 2 1 Oak St. Muncie, IN 54545
Terry Smith 3 1 Pine Ave. Palatka, FL 32273
Pat Jones 4 1 Lake Dr. Erie, PA
Frank Smith 5 1 Minerva La Ronkonkoma, NY
Joe Blow 23 2 Pond View Dr. Santa Barbara, CA
Sue Banks 14 2 Puppy Dog Tr. Walla Walla, WA 97654
Al Adams Martin Luther King Hwy El Paso, NM 83536
Uh-oh what about city now?
This is why text files are of limited use and DBMS are so important

129. 4/20/2018
Processing Data
Control breaks are interuptions in normal program execution
Like when a record was modified
Normal processing was copying the data from the customer file to the temp file
When the customer to change was reached, different instructions were performed
The new info was retrieved from the user and written to the temp file
Then the copying continued
Control breaks used frequently when printing reports

130. Control Breaks Example, a report that has the following format:
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Control Breaks
Example, a report that has the following format:
Report header (on first page)
For each subsequent page
A page header with page number
For next 33 items
Print line item (from file data)
A page footer with page number
Report footer (on last page)

131. Detailed Wisconsin Sales Report – page 2
Control Breaks
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Wisconsin State
Sales Report
Detailed Wisconsin Sales Report – page 2
xxxxx xxxxxxxx xxxxxxx xxxxxxx xxxx xxxxxxxxx xxxxxxx xxxxx xxxxx xxxxx xxxxxxxx xxxxxxx xxxxxxx xxxx xxxxxxxxx xxxxxxx
: : : : : : : : : : : : : : : :
End of page 2

132. Detailed Wisconsin Sales Report – page 3
Control Breaks
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Detailed Wisconsin Sales Report – page 3
xxxxx xxxxxxxx xxxxxxx xxxxxxx xxxx xxxxxxxxx xxxxxxx xxxxx xxxxx xxxxx xxxxxxxx xxxxxxx xxxxxxx xxxx xxxxxxxxx xxxxxxx
: : : : : : : : : : : : : : : :
End of page 3
End of
Wisconsin State
Sales Report

133. Control Breaks Module main() Declare Integer pageCtr = 1, lineCtr = 0
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Control Breaks
Module main()
Declare Integer pageCtr = 1, lineCtr = 0
Declare String reportHeader = "Wisconsin State Sales Report "
Declare String pageHeader = " Detailed Wisconsin Sales Report – page "
Declare String pageFooter = " End of page "
Declare String reportFooter = " End of Wisconsin State Sales Report"
Display reportHeader
Skip to next page
pageCtr = pageCtr + 1
// Declare and open the file
Declare InputFile salesFile
Open salesFile "sales.dat"
// Priming read
Read salesFile tempVariable

134. Use Nested Loops Inner Loop Outer Loop While (not eof)
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Use Nested Loops
While (not eof)
Display pageHeader, pageCtr
While (lineCtr < 33 AND not eof)
Display tempVariable lineCtr = lineCtr + 1
Read salesFile tempVariable
End While
lineCtr = 0
Display pageFooter, pageCtr
Skip to next page
pageCtr = pageCtr + 1
Display reportFooter
End Module
Inner
Loop
Outer
Loop

135. Points to Remember Files can hold many values of differing types
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Points to Remember
Files can hold many values of differing types
Hold data permanently
Progam ends but data is still in the file
Just as with arrays, easiest to process files with loops

136. Assignments Non-Graded Graded Chap 9 labs 9.1-9.3 Chap 9 lab 9.4
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Assignments
Non-Graded
Chap 9 labs
Graded
Chap 9 lab 9.4