Using Predefined Classes and Methods in a Program

1
Using Predefined Classes and Methods in a Program

• Many predefined packages, classes, and methods in
  Java
• Library Collection of packages
• Package Contains several classes
• Class Contains several methods
• Method Set of instructions

2
Using Predefined Classes and Methods in a Program

• To use a method you must know
• Name of class containing method (Math)
• Name of package containing class (java.lang)
• Name of method (pow), its parameters (int a, int
  b), and function (ab)

3
Using Predefined Classes and Methods in a Program

• Example method call
• import java.lang //imports package
• Math.pow(2,3) //calls power method in
  //class Math
• (Dot) . Operator used to access the method in
  the class

4
The class String

• String variables are reference variables
• Given String name
• Equivalent Statements
• name new String("Lisa Johnson")
• name Lisa Johnson

5
The class String

• The String object is an instance of class string
• The value Lisa Johnson is instantiated
• The address of the value is stored in name
• The new operator is unnecessary when
  instantiating Java strings
• String methods are called using the dot operator

6
Commonly Used String Methods

• String(String str)
• char charAt(int index)
• int indexOf(char ch)
• int indexOf(String str, int pos)
• int compareTo(String str)

7
Commonly Used String Methods

• String concat(String str)
• boolean equals(String str)
• int length()
• String replace(char ToBeReplaced, char
  ReplacedWith)
• String toLowerCase()
• String toUpperCase()

8
Input/Output

• Input Data
• Format Input
• Output Results
• String Tokenization
• Format Output
• Read From and Write to Files

9
Using Dialog Boxes for Input/Output

• Use a graphical user interface (GUI)
• class JOptionPane
• Contained in package javax.swing
• Contains methods showInputDialog and
  showMessageDialog
• Syntax
• str JOptionPane.showInputDialog(strExpression)
• Program must end with System.exit(0)

10
Parameters for the Method showMessageDialog
11
JOptionPane Options for the Parameter messageType
12
JOptionPane Example
13
Tokenizing a String

• class StringTokenizer
• Contained in package java.util
• Tokens usually delimited by whitespace characters
  (space, tab, newline, etc)
• Contains methods
• public StringTokenizer(String str, String
  delimits)
• public int countTokens()
• public boolean hasMoreTokens()
• public String nextToken(String delimits)

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Formatting the Output of Decimal Numbers

• Type float defaults to 6 decimal places
• Type double defaults to 15 decimal places

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class Decimal Format

• Import package java.text
• Create DecimalFormat object and initialize
• Use method format
• Example
• DecimalFormat twoDecimal
• new DecimalFormat("0.00")
• twoDecimal.format(56.379)
• Result 56.38

16
File Input/Output

• File area in secondary storage used to hold
  information
• class FileReader is used to input data from a
  file
• class FileWriter and class PrintWriter send
  output to files

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File Input/Output

• Java file I/O process
• Import classes from package java.io
• Declare and associate appropriate variables with
  I/O sources
• Use appropriate methods with declared variables
• Close output file

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Inputting (Reading) Data from a File

• Use class FileReader
• Specify file name and location
• Create BufferedReader Object to read entire line
• Example

BufferedReader inFile new BufferedReader(new
FileReader("a\\prog.dat"))
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Storing (Writing) Output to a File

• Use class FileWriter
• Specify file name and location
• Utilize methods print, println, and flush to
  output data
• Example

PrintWriter outFile new PrintWriter(new
FileWriter("a\\prog.out"))
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Skeleton of I/O Program
21
Programming Example Movie Ticket Sale and
Donation to Charity

• Input movie name, adult ticket price, child
  ticket price, number of adult tickets sold,
  number of child tickets sold, percentage of gross
  amount to be donated to charity
• Output

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Programming Example Movie Ticket Sale and
Donation to Charity

• Import appropriate packages
• Get inputs from user using JOptionPane.showInputDi
  alog
• Parse and format inputs using DecimalFormat
• Make appropriate calculations
• Display Output using JOptionPane.showMessageDialog
  

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Movie Ticket Sale and Donation to Charity

• import javax.swing.JOptionPane
• import java.text.DecimalFormat
• public class MovieTicketSale
• public static void main(String args)
• //Step 1
• String movieName
• String inputStr
• String outputStr
• double adultTicketPrice
• double childTicketPrice
• int noOfAdultTicketsSold
• int noOfChildTicketsSold
• double percentDonation
• double grossAmount
• double amountDonated
• double netSaleAmount

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Movie Ticket Sale and Donation to Charity

• DecimalFormat twoDigits new DecimalFormat("0.00"
  ) //Step 2
• movieName JOptionPane.showInputDialog
• ("Enter the movie
  name") //Step 3
• inputStr JOptionPane.showInputDialog
• ("Enter the price of an adult
  ticket") //Step 4
• adultTicketPrice Double.parseDouble(inpu
  tStr) //Step 5
• inputStr JOptionPane.showInputDialog
• ("Enter the price of a child
  ticket") //Step 6
• childTicketPrice Double.parseDouble(inpu
  tStr) //Step 7
• inputStr JOptionPane.showInputDialog
• ("Enter number of adult
  tickets sold") //Step 8
• noOfAdultTicketsSold Integer.parseInt(in
  putStr) //Step 9
• inputStr JOptionPane.showInputDialog
• ("Enter number of child
  tickets sold") //Step 10

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Movie Ticket Sale and Donation to Charity

• grossAmount adultTicketPrice
  noOfAdultTicketsSold
• childTicketPrice
  noOfChildTicketsSold //Step 14
• amountDonated grossAmount
  percentDonation / 100 //Step 15
• netSaleAmount grossAmount -
  amountDonated //Step 16
• outputStr "Movie Name " movieName
  "\n"
• "Number of Tickets Sold "
• (noOfAdultTicketsSold
• noOfChildTicketsSold)
  "\n"
• "Gross Amount "
• twoDigits.format(grossAmount
  ) "\n"
• "Percentage of Gross Amount
  Donated "
• twoDigits.format(percentDona
  tion) "\n"
• "Amount Donated "
• twoDigits.format(amountDonat
  ed) "\n"
• "Net Sale "
• twoDigits.format(netSaleAmou
  nt) //Step 17

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Programming Example Student Grade

• Input file containing students first name, last
  name, five test scores
• Output file containing students first name,
  last name, five test scores, average of five test
  scores

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Programming ExampleStudent Grade

• Import appropriate packages
• Get input from file using BufferedReader and
  FileReader
• Tokenize input from file using StringTokenizer
• Format input and take average of test scores
• Open and write to output file using PrintWriter
  and FileWriter
• Close files

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STUDENT GRADE

• //Program to calculate average test score.
• import java.io.
• import java.util.
• import java.text.DecimalFormat
• public class StudentGrade
• public static void main (String args)
  throws IOException,
• 
  FileNotFoundException
• //Declare and initialize variables
  //Step 1
• double test1, test2, test3, test4, test5
• double average
• String firstName
• String lastName
• StringTokenizer tokenizer

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STUDENT GRADE

• BufferedReader inFile new
• BufferedReader(new
  FileReader("e\\cecs261/student/test.txt"))
  //Step 2
• PrintWriter outFile new
• PrintWriter(new FileWriter("e\\testa
  vg.out")) //Step 3
• DecimalFormat twoDecimal
• new
  DecimalFormat("0.00") //Step 4
• tokenizer
• new StringTokenizer(inFile.readLine(
  )) //Step 5
• firstName tokenizer.nextToken()
  //Step 6
• lastName tokenizer.nextToken()
  //Step 6
• outFile.println("Student Name "
• firstName " "
  lastName) //Step 7

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STUDENT GRADE

• //Step 8-Retrieve five test scores
• test1 Double.parseDouble(tokenizer.nextT
  oken())
• test2 Double.parseDouble(tokenizer.nextT
  oken())
• test3 Double.parseDouble(tokenizer.nextT
  oken())
• test4 Double.parseDouble(tokenizer.nextT
  oken())
• test5 Double.parseDouble(tokenizer.nextT
  oken())
• outFile.println("Test scores "
• twoDecimal.format(test1)
  " "
• twoDecimal.format(test2)
  " "
• twoDecimal.format(test3)
  " "
• twoDecimal.format(test4)
  " "
• twoDecimal.format(test5))
  //Step 9

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STUDENT GRADE

• average (test1 test2 test3 test4
  test5)/5.0 //Step
  10
• outFile.println("Average test score "
• twoDecimal.format(average)
  ) //Step 11
• outFile.close()
  //Step 12