ISYE 7210--Simulation of Real-Time Systems Fall 2005 Classes

1
ISYE 7210--Simulation of Real-Time Systems Fall
2005 Classes ObjectsNote See zip file on
class Web page for examples used in
classwww.chmsr.gatech.edu/ISyE7210/
www.horstmann.com/corejava.html Q 5.day.5
9/20/2005 913 PM

• Christine M. Mitchell
• Center for Human-Machine Systems Research (chmsr)
• School of Industrial and Systems Engineering
• (chmsr lab) ISyE Main, Room 426, 404 385-0363
• (office) ISyE Groseclose, Room 334, 404 894-4321
• cm_at_chmsr.gatech.edu

2
StringOverload API

• Class Name
• StringOverload()
• Variables
• private long quantity
• Constructor
• public class StringOverload()
• Methods
• public long getQuantity()--returns value of
  quantity
• public long setQuantity(long newQuant)
• --set private variable, quantity,
• public String toString()
• --returns string representation of the object

3
Variable Scope

• Scope
• Region of a program within which the variable can
  be referred to by simple name
• Determines if variable can be used from outside
  of the class
• Location of the variable declaration establishes
  its scope category
• Local variable
• Data item known within a block
• Inaccessible to code outside the block.
• Member variable
• Field of a class
• Default is not static
• Method parameter
• Exception-handler parameter
• Distinct from visibility
• Set with an access modifier

4
Basic Java Syntax Classes Plus our Coding
Conventions (contd)(Example 1 Part.java)

• A Java class has two components
• A class declaration
• A class body
• A Java class declaration includes specification
  of scope class name
• public Part (for class Part) //first line of
  class definition
• Class scope (access modifier) public, private,
  protected,
• Note An access modifier controls which other
  parts of a Java program can see the Java class
• A public scope means any other part of the Java
  program can see the class

5
Overview Classes

• A Java class is a template that describes the
  form of a variable an object (instance) of that
  class
• Class objects (instances) name yourName
• String name String yourName
• Class template
• Class declaration
• Class scope
• Attributes of the class
• access level public, private, protected
• abstract cannot be instantiated
• final cannot have a subclass
• extends descends from a superclass
• implements includes specification of variable
  and method details defined in an interface
• Class name
• Class defaults nonpublic, nonabstract, nonfinal
  subclass of Object that implements no interfaces.

6
Overview Classes (contd)

• A Java class template (contd)
• 2. Class body
• a. Variables of the class may not be defined
  within the body of a method
• Types of variables in a class
• Instance variables one for every instance of a
  class
• class variables exactly one for each class
• Access public, private, protected
• Type variable (int, float, .) or an instance of
  another class
• static a class variable
• final a constant
• static final a class constant
• static final double INTEREST_RATE .04

7
Class Definition Summary (contd)

• A Java class template (contd)
• class body
• b. Constructors
• Special functions that create an instance (an
  object) of the class
• Must have the same name as the class
• Do not have a return type
• Qualifiers
• access level public, private, protected
• arguments (type anArgumentName, ..)
• Default constructor
• Java creates a default constructor that sets all
  the variables of the class to their natural
  defaults, if the user does not create ANY
  constructor!!!!!
• If the user creates one or more constructors,
  then Java does NOT create a default constructor
  the user may create a default constructor

8
Class Definition Summary (contd)

• A Java class template (contd)
• class body
• b. constructors
• Use of constructors
• One step method declare initialize an instance
  of ClassName, objectName, simultaneously
• ClassName objectName new ClassName()
• Two step method
• (1) Declare a reference variable of type
  ClassName, objectName
• (2) Initialize (and create memory) for the
  instance
• (1) ClassName objectName null
  //initialization is optional
• (2) objectName new ClassName() //allocate
  memory
• (1) Integer anInt 0 //declare an instance
• (2) anInt new Integer (700) //initialize

9
Class Definition Summary (contd)

• A Java class template (contd)
• class body
• c. Destructors
• Java does not have destructor methods for a class
• Java reclaims memory with garbage collection
• Garbage collection happens in the background
• Users are rarely aware of garbage collection
• If speed is an issue (almost never!!), the
  programmer can force garbage collection
• Do not do without thinking
• In ten years, I never had to explicitly call Java
  garbage collection explicitly

10
Example Part (a more sophisticated class)
Part.2aTest a Java-Created Default Constructor

• //Part.java (Part.2a--with Java created default
  constructor)
• /
• A more complicated Part class.
• /
• public class Part
• /
• instance variables
• /
• private int numParts 25 //good to
  initialize
• /
• Constructors (special class members)
• Create an instance (object) of a class
• Constructors must have the same name as the
  class
• /
• /
• Default constructor automatically created
  by Java

11
Example Part (a more sophisticated class)
Part.2aTest a Java-Created Default Constructor

• //Part.java (Part.2a--with Java created default
  constructor)
• /
• Constructor sets initial value of numParts
• /
• //public Part (int newParts) //must have the
  same name as the class
• //
• //numParts numParts //sets the instance
  variable to numParts
• //
• /
• Accessor methods return the values of
  variables in a class
• Accessor methods are typically called,
  getVariableName()
• ltpgt
• Returns the value of private instance
  variable numParts
• /
• public int getNumParts()
• return numParts

12
Example Part (a more sophisticated class)
Part.2aTest a Java-Created Default Constructor

• //Part.java (Part.2a--with Java created default
  constructor)
• /
• Mutator methods change the values of
  variables in a class
• Mutator methods are typically called,
  setVariableName(int aNumber.)
• ltpgt
• Changes the value of private instance
  variable _numParts
• /
• public void setNumParts(int newNum)
• numParts newNum
• return //optional
• /
• Other instance methods change the values of
  variables in a class
• ltpgt
• Increments the value of numParts by 10
• /
• public void incrementNumParts()

13
Example Part.2a (a more sophisticated class)
Test a Java-Created Default Constructor

• //Part.java (Part.2a--with Java created default
  constructor)
• /
• Increments the value of numParts by
  anIncrease
• /
• public void incrementNumParts(int anIncrease)
• numParts numParts anIncrease
• /
• Overload toString() method of class Object
• /
• public String toString()
• String s new String(numParts " parts in
  this batch" )
• return s

14
Example Part (a more sophisticated class)
Part.2aTest a Java-Created Default Constructor

• //Part.java (Part.2a--with Java created default
  constructor)
• public static void main (String args)
• //create two instance of Part
• //test default constructor
• Part testPart new Part() //the one line
  method of creating an instance of Part
• System.out.println ("testPart Has "
  testPart.toString() ".")
• //Part myPart //reference to a Part object
• //myPart new Part(85000) //now give it
  memory a value
• //Part yourPart new Part(2000) //the one
  line method of creating an instance of Part
• //System.out.println ("myPart Has "
  myPart.toString() ".")
• //System.out.println ("yourPart Has "
  yourPart.toString() ".")
• //System.out.println ("yourPart Has "
  yourPart.toString() ".")
• //yourPart.setNumParts(2500)
• //System.out.println ("yourPart has "
  yourPart.toString() ".")
• //yourPart.incrementNumParts(1000)

15
Example Part (a more sophisticated class)
Part.2b Overloaded Default Constructors
Other Methods

• //Part.java (Part.2b--constuctors default
  overloaded)
• /
• A second, more complicated Part class.
• /
• public class Part
• /
• instance variables
• /
• private int numParts 25 //good to
  initialize
• /
• Constructors (special class members)
• Create an instance (object) of a class
• Constructors must have the same name as the
  class
• /

16
Example Part (a more sophisticated class)
Part.2b Overloaded Default Constructors
Other Methods

• //Part.java (Part.2b--constuctors default
  overloaded)
• public Part ( ) //user-created default
  constructor no argument
• numParts 25 //sets a default instance
  variable to four for numPart
• /
• Overloaded constructor sets initial value of
  numParts
• /
• public Part (int newParts) //must have the
  same name as the class
• numParts newParts //sets the instance
  variable numParts
• /
• Accessor methods return the values of
  variables in a class
• Accessor methods are typically called,
  getVariableName()
• ltpgt
• Returns the value of private instance
  variable numParts

17
Example Part (a more sophisticated class)
Part.2b Overloaded Default Constructors
Other Methods

• //Part.java (Part.2b--constuctors default
  overloaded)
• /
• Mutator methods change the values of
  variables in a class
• Mutator methods are typically called,
  setVariableName(int aNumber.)
• ltpgt
• Changes the value of private instance
  variable numParts
• /
• public void setNumParts(int newNum)
• numParts newNum
• return //optional
• /
• Other instance methods change the values of
  variables in a class
• ltpgt
• Increments the value of numParts by 10
• /

18
Example Part (a more sophisticated class)
Part.2b Overloaded Default Constructors
Other Methods

• //Part.java (Part.2b--constuctors default
  overloaded)
• /
• Increments the value of numParts by
  anIncrease
• /
• public void incrementNumParts(int anIncrease)
• numParts numParts anIncrease
• /
• Overload toString() method of class Object
• /
• public String toString()
• String s new String(numParts " parts in
  this batch" )
• return s

19
Example Part (a more sophisticated class)
Part.2b Overloaded Default Constructors
Other Methods

• //Part.java (Part.2b--constuctors default
  overloaded)
• public static void main (String args)
• //create two instance of Part
• //test default constructor
• //Part testPart new Part() //the one
  line method of creating an instance of Part
• //System.out.println ("testPart Has "
  testPart.toString() ".")
• Part myPart //reference to a Part object,
  myPart
• myPart new Part(85000) //now give it
  memory a value
• System.out.println ("myPart Has "
  myPart.toString() ".")
• Part yourPart new Part(2000) //the one
  line method of creating an instance of Part
• System.out.println ("yourPart Has "
  yourPart.toString() ".")
• yourPart.setNumParts(2500)
• System.out.println ("yourPart now has "
  yourPart.toString() ".")
• yourPart.incrementNumParts(1000)

20
Example Part.2c (multiple Java files)

• Part.2c contains two Java source files
• Part.java // same file as in 2b
• TestApp.java //new
• TestApp.java
• TestApp tests the functionality of Part class
• TestApp has one method, main(),
• Alternative to Example 2b in which the main()
  contained in Part was used to test Part
• Compiling multiple files in Java
• Remove all class files in folder Part.2c
• Compile TestApp
• Look in folder, Part.2c
• You will see a Part.class as well as a
  TestPart.class
• Java compiler is smart enough to see it needs a
  Part class looks for one compiles it as well
• Like a make command in Unix

21
Example Part.2c (multiple Java files)

• //TestApp.java (Part.2c multiple Java files)
• /
• This is a standard testing program class.
• ltpgt
• It can be used with any class or set
• of classes.
• ltpgt
• Testing Part from with two files Part.java
  TestApp.java
• and the main() is in class TestPart
• /
• public class TestPart
• public static void main (String args)
• //create two instances of Part with default
  constructor
• Part myPart new Part( ) //the one line
  method of creating an instance

22
Example Part.2c (multiple Java files)

• //TestApp.java (Part.2c multiple Java files)
• //use mutator methods to change the instance
  variables for both objects
• myPart.setNumParts(1000)
• yourPart.setNumParts(-50)
• System.out.println ("I have "
  myPart.getNumParts( ) " parts.")
• System.out.println ("You have "
  yourPart.getNumParts( ) " parts.")
• //increment the value of private instance
  variable, numParts in myPart
• myPart.incrementNumParts()
• yourPart.incrementNumParts(2000)
• System.out.println ("I have "
  myPart.getNumParts( ) " parts.")
• System.out.println ("You have "
  yourPart.getNumParts( ) " parts.")
• Part hisPart //create a reference (2) line
  method of construction
• hisPart new Part(85000) //overloaded
  constructor that initialize instance var.
• Part herPart new Part(2000) // (1) line
  method of creating an instance of Part
• System.out.println ("herPart"
  herPart.toString() ".")
• System.out.println ("hisPart "
  hisPart.toString() ".")

23
Example Part.2c (multiple Java files)

• //TestApp.java (Part.2c multiple Java files)
• Output
• yourPart 25 parts in this batch.
• yourPart 350 parts in this batch.
• I have 25 parts.
• You have 350 parts.
• I have 1000 parts.
• You have -50 parts.
• I have 1010 parts.
• You have 1950 parts.
• herPart2000 parts in this batch.
• hisPart 85000 parts in this batch.