An Introduction to Java Programming and Object-Oriented Application Development

1
An Introduction to Java Programming and
Object-Oriented Application Development

• Chapter 7
• Characters, Strings, and Formatting

2
Objectives

• In this chapter you will
• Use the Character wrapper class to work with
  characters
• Employ several methods of the Character class
• Explore how to manipulate strings using the
  StringBuilder class
• Use the StringTokenizer class to break strings
  into tokens
• Perform sophisticated string formatting using the
  printf and format methods

3
Working with Characters

• Recall char and String from Chapter 2
• Recall the String class methods equals and
  substring from Chapter 5
• Brief review of the char data type
• Methods in the Character class

4
Brief Review of the char Data Type

• Recall a char is one of eight primitive types
• A character is any symbol represented by Unicode
• Always expressed inside single quotes
• Every individual character has an equivalent
  integer value
• The methods of the Character class manipulate
  characters

5
Brief Review of the char Data Type (continued)
6
Methods in the Character Class

• The Character class is a wrapper class
• The Integer and Double classes are also wrapper
  classes
• Each primitive type has a corresponding wrapper
  class
• A wrapper class holds the value of a primitive
  type within an object so methods can be applied

7
Methods in the Character Class (continued)

• charValue retrieves the character stored in the
  Character object
• compareTo returns the difference in Unicode
  values for two characters
• equals is true if two characters are identical
• isDigit is true if a character is in 0-9
• isLetter is true if a character is in a-z or A-Z

8
Methods in the Character Class (continued)

• isWhiteSpace is true if the character is a space
• isWhiteSpace returns false if the character is
  newline, tab, etc.
• toLowerCase changes uppercase to lowercase
• toUpperCase changes lowercase to uppercase

9
Apply the Concept

• Develop an application to check the validity of a
  password
• Must be between 8 and 15 characters in length
• May not contain spaces
• Must contain at least one nonnumeric uppercase
  character and one nonnumeric lowercase character
• Must contain at least one numeric digit

10
Apply the Concept (continued)

• Several boolean variables track whether the
  password is valid
• The number of characters is determined with
  length from the String class
• A loop examines each character
• Uses the charAt method to extract each character
• Tested using isWhiteSpace, isDigit, isLowerCase,
  isUpperCase

11
Apply the Concept (continued)

• If the appropriate character is found, boolean
  variable set to true
• Errors appended to an error message
• An ifelse statement tests if the password is
  valid (i.e. all booleans set appropriately)
• Either the error message is displayed, or a
  message saying the password is valid

12
Apply the Concept (continued)

• if statements test each validity rule
• Each if statement tests for a required character
• In the case of white space, a prohibited
  character
• If the character is found and it is the first one
• if statement is executed
• flag is set to true
• If the character is found and it is not the
  first, the statement is skipped
• Programs using Boolean logic are prone to error
  and must be extensively tested

13
Apply the Concept (continued)
14
Working with Strings

• Coming next
• Brief review of the String class
• The StringBuilder class
• The StringTokenizer class

15
Brief Review of the String Class

• Recall a string is an object
• String myStr Johnson
• String myStr new String(Johnson)
• Recall the methods equals, length and substring
• A string is a reference variable that contains
  the memory address of an array of characters
• Two classes StringBuilder and StringTokenizer
  manipulate strings

16
Brief Review of the String Class (continued)

• StringBuilder provides methods to manipulate and
  build strings
• StringTokenizer breaks strings into tokens
• A token is a group of characters within a string
• Tokens are separated by delimiters
• The tokens in this sentence are delimited by
  white space

17
The StringBuilder Class

• A String object is immutable
• Once created it can never be changed
• StringBuilder allows strings to be modified
• StringBuilder is in java.lang
• All methods in StringBuilder are nonstatic

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The StringBuilder Class (continued)

• append adds text to an existing StringBuilder
  object
• insert inserts a second argument just after the
  position given by the first argument
• deleteCharAt deletes a single character from a
  StringBuilder at a given position
• replace replaces all occurrences of one character
  with another
• toString creates a string that contains the data
  from the StringBuilder object

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The StringTokenizer Class

• StringTokenizer is in java.util
• Breaks a string into tokens
• Create the string to be tokenized
• Create the StringTokenizer object linked to the
  string
• Apply the StringTokenizer object to the string to
  get a token
• nextToken and countTokens are nonstatic

20
Apply the Concept

• Develop an application that takes a name and a
  Social Security number and reformats them
• Test the input to determine if it is acceptable
• Data is reformatted
• Name reformatted to print the last name first
• Hyphens removed from Social Security number
• Application is broken into methods

21
Apply the Concept (continued)

• Four method calls follow the variable declaration
• getName gets the name from the user
• getSsn gets the SSN from the user
• createOutputName formats the name
• createOutputSsn formats the SSN
• main method concludes with the display of the
  output

22
Apply the Concept (continued)

• getName and getSsn are similar
• nameTokenizer in getName is a different memory
  address than nameTokenizer in main
• Both nameTokenizer variables contain a reference
  to the same StringTokenizer object
• nameTokenizer is instantiated using the input
  string
• An if statement tests for 3 tokens

23
Apply the Concept (continued)

• A dowhile loop repeats and prompts the user for
  correct input
• getName returns to main when the dowhile loop
  terminates
• The method createOutputName extracts first,
  middle, and last names, and stores them in an
  array
• The name array is appended to a StringBuilder
  object
• The StringBuilder is converted to a string and
  returned to main

24
Apply the Concept (continued)
25
Formatting Data for Output

• Output to the terminal with System.out.print and
  System.out.println
• Output to a GUI window using JOptionPane.showMessa
  geDialog
• Formatting with ( ) and NumberFormat
• Next printf in the PrintStream class in java.io
• format in the Formatter class in java.util

26
The printf and format Methods

• We have been using System.out.println and string
  concatenation ( )
• Instead of print and println, use printf and
  format

27
The printf and format Methods (continued)
28
The printf and format Methods (continued)
29
The printf and format Methods (continued)

• printf takes a format string and a string
  variable printf(Cost .2f\n, cost )
• The format specifier begins with , ends with a
  conversion character .2f
• Conversion suffix characters may follow the
  conversion characters
• Integers use conversion characters d and x
• Floating points use conversion characters e, E,
  f, and g

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The printf and format Methods (continued)

• Characters and strings use the conversion
  characters C and S
• Dates and times use the conversion character t,
  possibly with suffix characters C, A, B, d, Y
• The argument index specifies the argument to
  which the format specifier applies
• 1 is the first, 2 is the second,, n is the
  nth
• The field width is the number of spaces an
  argument occupies
• The precision is the number of decimal places

31
The format Method

• The printf method displays to the command window
• printf cannot be used to output to a GUI or file
• The format method in the Formatter class can
  output to a GUI or file
• format is identical to printf

32
The format Method (continued)
33
Case Study MusicWorld

• Recall MusicWorld allows a user to input titles
  of CDs for purchase
• The total, including quantity discount and tax,
  is displayed at the end
• Eventually, the purchase information will be
  stored in a database
• Information in a database must be associated with
  a unique identifier
• Use date and time to create an order identifier

34
Flowcharts for New Features of MusicWorldApp7.java
New variables are added Old variables are removed
35
Flowcharts for New Features of MusicWorldApp7.java
(continued)

• The method displayOrderID uses the current time
  and date to create a unique order ID
• The main method calls displayOrderOutput
• The method displayOrderOutput calls the method
  createOrderID
• The method createOrderID performs the majority of
  the formatting
• The identifier is in the form YYMMDDHHMMSS

36
Program Code for MusicWorldApp7.java

• The only changes from MusicWorldApp6.java are in
  three methods
• displayItemOutput
• displayOrderOutput
• createOrderID
• Each method will be discussed next

37
The displayItemOutput Method

• Line 147 is the format string to be used in
  printf s\n\nss\nss\ns.2f\nsd\ns.2f\
  n\ns.2f\n\ns
• There must be exactly one argument for every
  format specifier
• The first s corresponds to the variable
  headerStr
• The second s corresponds to the literal CD ID

38
The displayOrderOutput Method

• Lines 184-185 create a DateFormat object
• The argument Locale.FRENCH causes the date to be
  in the format YY/DD/MM and time to be in 24-hour
  format
• createOrderID is called, and returns the order ID
• The order ID is appended to a StringBuilder
• The StringBuilder is converted to a string and
  displayed to the console

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The createOrderID Method

• A StringBuilder object is instantiated
• Methods of the StringBuilder class are used to
  delete and rearrange its parts
• The StringBuilder object is created to a string
  and returned to displayOrderID
• In Chapter 9, the program will write the
  information to a file

40
Summary

• Characters are represented by Unicode values
• The Character class is a wrapper class for
  characters
• All primitive types have wrapper classes to allow
  methods to act upon the primitive value
• StringBuilder allows strings to be manipulated
• StringTokenizer breaks strings into tokens
  separated by delimiters

41
Summary (continued)

• All methods in StringBuilder and StringTokenizer
  are nonstatic
• The method printf is in the class PrintStream and
  formats strings
• The method format is in the class Formatter and
  operates identically to printf
• The method format can direct formatting to a GUI
  window or a file