Getting Started with Java

1
Chapter 2

• Getting Started with Java
• Part B

2
Topics

• Components of a Java Program
• classes
• methods
• comments
• import statements
• Declaring and creating objects
• Java identifiers
• Standard Java classes
• Development Example

3
Warm-up Exercises

• First homework assignment (on the web)
• Chapter 1 problems 2, 4, 5
• Chapter 2 problems 1, 9 (parts a, c, g, j) , 12
• Practice
• Chapter 1 3 CD class
• Chapter 1 14 Inheritance hierarchy for contact
  manager (Person, Professional contact, Friend,
  Student)

4
UML Class Diagrams

• An example of a UML diagram for the CD class
• Diagram has only instance data and methods
• Class data and methods would be underlined

5
Inheritance Hierarchy
6
Template for Java Program
7
Edit-Compile-Run Cycle

• Edit
• vi MyClass.java
• Compile
• javac MyClass.java
• Run
• java MyClass

8
Java Standard Classes

• Java comes with an extensive set of classes that
  you can use.
• Using existing Java classes is an important step
  in becoming a successful and proficient
  programmer.
• The standard classes are organized into packages

9
Standard Classes

• We will introduce four standard classes here
• String
• JOptionPane
• Date
• SimpleDateFormat

10
String

• A string is basically some text
• a sequence of characters
• We've seen String objects in our programs already
• "this is a String"
• These are constant or literal String objects
• They have no name
• They can't be changed
• String class is in java.lang (no import statement
  required)

11
Creating Strings

• Putting a literal string in your program creates
  a String automatically
• You can declare a String object and assign it to
  the literal String
• String fixedString "some text"
• the String class is the only one you can do this
  with
• You can use new to create a new String from an
  existing one
• String newString new String( "more text")
• String newString2 new String( newString)

12
String Methods

• The String class has many methods
• We'll look at a few
• length() returns the number of characters in the
  String
• String text "Espresso"
• text.length() returns 8
• String concat( String toAdd) creates a new String
  out of the original String followed by the
  argument String
• Can use as a shortcut for this method (another
  unique property of the String class)
• "acro" "bat" is "acrobat"

13
indexOf method

• The indexOf method can be used to locate one
  String in another
• indexOf( String toFind) returns the position of
  toFind in the String
• Positions are numbered starting from 0
• the index of "press" in "Espresso" is 2
• if the toFind String isn't present, the result is
  -1

14
substring method

• substring returns a new String which is part of a
  larger String
• substring( start, justAfter)
• start is the desired starting index
• justAfter is the index of the first character
  past the desired substring

15
Using the substring method
16
Special Characters

• What if you need a string that has several lines
  of text in it?
• You can't spread a literal string over multiple
  lines
• You need to put a character into the string that
  represents a carriage return
• "\n" is a special character that represents a
  newline
• the \ is an escape character that tells the
  compiler to interpret the next character
  differently from its usual meaning
• We'll see other special characters that start
  with a \

17
GUI Windows

• Windows come in 2 forms in a GUI interface
• application windows which are generally
  long-lived
• JFrame objects in Java
• dialog boxes are short-lived
• JDialog objects in Java
• allow the user to interact with the program
• come in many forms - the JDialog class has to be
  quite complex to support this variety
• some common forms
• messages
• confirmation (yes/no/cancel)
• input

18
JOptionPane

• Allows you to easily create common types of
  JDialog objects
• All methods are class methods
• you never create a JOptionPane object
• call the methods using
• JOptionPane.methodName()
• JOptionPane is in the javax.swing package

19
Message Dialogs

• Used when you need to be sure the user has been
  informed about something
• results
• error messages and warnings
• JOptionPane.showMessageDialog( parent, message)
• parent is the name of the JFrame the JDialog is
  attached to (or null if it is not attached to a
  JFrame)
• message is the text to be displayed (a String)

20
Input Dialogs

• Another common form of dialog is one used to ask
  for a small amount of input
• JOptionPane.showInputDialog( String prompt)
• displays a box for the user to enter something
• returns the String that the user types in

21
Using Dates in Java

• The Date class in Java represents time to the
  nearest millisecond
• Create a Date with the current time using
• Date today new Date()
• The toString method of the Date class returns a
  String representing the complete time and date
• Weekday Month day hoursminutesseconds timezone
  year
• Date is in java.util

22
Other Date Formats

• Use the SimpleDateFormat class
• Create a SimpleDateFormat object with a "picture"
  of what you want it to look like
• picture is a string with codes for the various
  fields
• SimpleDateFormat sdf new SimpleDateFormat("MM/dd
  /yyyy")
• SimpleDateFormat is in the java.text package

23
SimpleDateFormat Codes
Y year number yyyy-gt2004
M month text or number MM-gt10 MMM-gt Oct
d day in month number dd-gt20
h hour in (am/pm) number hh-gt09
a am/pm text a-gtam
m minutes in hour number mm-gt35
s seconds in minute number ss-gt54
E day in week text E-gt Sat.
24
Software Lifecycle

• The sequence of stages from conception to
  operation of a program is called software life
  cycle.
• Five stages are
• Analysis
• Design
• Coding
• Testing
• Operation and Maintenance

25
Sample Development Printing Initials

• Problem statement
• Write an application that asks for the users
  first, middle, and last names and replies with
  their initials.
• Overall plan
• Get the users first, middle, and last names.
• Extract the initials to form the monogram.
• Output the monogram.

26
What classes do we need?
27
Necessary classes

• Name, initials and monogram need String
• Need JOptionPane for input and output
• To input the name, we need an input dialog
• To output the monogram, we need a message dialog

28
UML Diagram for Ch2Monogram
29
Phase 1

• Input the user's name
• first middle last
• Choices
• one dialog for each part
• easy to program
• tedious for user
• single dialog for the entire name
• harder to program
• need to specify format in this case
• nicer for user

30
Phase 2

• Compute and display monogram
• need to display result to know whether
  computation is correct
• How to separate name into 3 parts?
• use indexOf to find space
• use substring to separate at space
• repeat for second space
• How to get initial from each part?
• substring(0,1)