Methods

1
Methods Simple Control Structures
2
Parameters

• So far our methods (or member functions) have
  done very little we really don't know how to
  make them do much (yet)
• One thing we would lie to do is to pass
  information into and out of a method.

3
Passing information to a Method

• The parenthesis behind a function name can
  contain "formal parameters". A formal parameter
  is a sort of placeholder or local name for a
  value being passed in.
• The type of the formal parameter must be
  specified and the item passed must be of the
  specified type. (We like to know what we are
  getting!)

4
Accessor and Mutator Methods(also known as
get/set methods)

• We often want to keep some information private to
  an object. So, we declare it as private meaning
  only the object itself can use the information
  directly.
• This means that we need to be able to initialize
  or set the value of the information and often to
  check on the value. This is what
  accessor/mutator methods are used for.

5
Another Sample Class

• / _at_author Jerry Heuring A sample class
  with accessor/mutator routines. The class
  represents a simple mailing address.
  /public class MailingAddress private String
  street private String city private String
  state private String postalCode// An mutator
  function for street public void setStreet (
  String s ) street s

6

• / A simple routine to print out the
  properties in this mailing address/public
  void printInfo( ) System.out.println(street)
  System.out.println(city) System.out.println(stat
  e) System.out.println(postalCode)
• / The main program will try to use an
  instance of the class. We will expand main as
  we add more methods./public static void main
  (String arguments) MailingAddress
  address1 address1 new MailingAddress() addr
  ess1.setAddress("2801 West Bancroft") address1.p
  rintInfo() System.exit(0)

7
Notes

• If we had tried to change the street
  directly address1.street "2801 West
  Bancroft"in the main it would not have allowed
  us to do so (because it is private).
• We could allow all of the properties to have set
  routines. (actually we will eventually)

8
Returning a Value From a Method

• You can return a value from a method as well. Up
  to now our methods have had a return type of
  "void" meaning they return nothing.
• You can return 1 (one) item using a return
  statement in a method. The value is returned to
  the calling method and object.
• Let's set up an accessor (get) for street

9
A Simple Accessor Function

• / function to return the current value for
  street. _at_return the current value for
  street/public String getStreet( ) return
  street

10
Notes

• By adding the get method the main program can now
  get the street value to use it. For
  example System.out.println(address1.street)
• Why use Accessor/Mutator methods?
• They are useful to hide details from the user.
  Also, if you need to make sure that something is
  within range it is nice to go through a mutator
  method.

11
A Completed Class

• What follows is a completed class for the
  MailingAddress object. It contains accessor and
  mutator routines for all private properties or
  instance variables.
• It looks long and complicated it isn't
  complicated!
• all set and get routines will follow the same
  pattern in this case only the property or
  instance variable will change.

12
Finished MailingAddress

• / _at_author Jerry Heuring Created Aug 17,
  2004 _at_version 0.0 Bugs Revisions
  Description This version of
  MailingAddress has the accessor/mutator
  functions (get/set functions) for all the private
  instance variables (or properties)./

13

• public class MailingAddress private String
  streetprivate String stateprivate String
  cityprivate String postalCode/ Mutator
  routine to set the street property _at_param s
  value to use to set street /public void
  setStreet( String s) street s /
  Accessor routine to get the street property
  _at_return a string representing the street
  /public String getStreet ( ) return street

14

• / Mutator routine to set the state
  property _at_param s value used to set the
  state Note The routine might want to
  check if it is a valid state name or
  abbreviation but we don't have the
  statements to do that yet. /public void
  setState( String s) state s
• / Accessor method to get the state
  property _at_return a string representing the
  state /public String getState( ) return
  state

15

• / Mutator method to set the city property
  _at_param c value that this city property is set
  to. /public void setCity(String c ) city
  c / Accessor method to get the city
  property _at_return a string representing the
  city /public String getCity( ) return
  city

16

• / Mutator method to set the postalCode
  property _at_param pc the postal code value that
  this postalCode will be set to.
  /public void setPostalCode(String
  pc) postalCode pc/ Accessor method
  to get the postalCode property _at_return a
  string representing a postalCode for this
  object. /public String getPostalCode( )
  return postalCode

17

• / Simple routine to print out all of this
  object's properties to System.out so that we
  can see them./public void printInfo()
  System.out.println(street) System.out.println
  (city) System.out.println(state) System.out.pr
  intln(postalCode) / The main program
  instantiates (creates) an instance of mailing
  address and then uses each of the methods to
  test whether or not they work. _at_param
  arguments the command line arguments -- unused.
  /public static void main(String arguments)
  MailingAddress address1 address1 new
  MailingAddress() address1.setStreet("2801
  West Bancroft") address1.printInfo( )

18

• address1.setCity("Toledo") address1.setState("O
  hio") address1.setPostalCode("43606") address1
  .printInfo() System.out.println(address1.getSt
  reet() ) System.out.println(address1.getCity()
  ", " address1.getState(
  )) System.out.println(" "
  address1.getPostalCode( ))
• System.exit(0)