1. Chapter 8: User-Defined Classes and ADTs
Java Programming:
Program Design Including Data Structures

2. Chapter Objectives Learn about classes
Learn about private, protected, public, and static members of a class
Explore how classes are implemented
Learn about the various operations on classes
Java Programming: Program Design Including Data Structures

3. Chapter Objectives (continued)
Examine constructors and finalizers
Examine the method toString
Learn about the abstract data type (ADT)
Java Programming: Program Design Including Data Structures

4. Classes class: collection of a fixed number of components
Components: Members of a class
Members are accessed by name
Class categories/modifiers:
private
public
protected (discussed at chapter 11)
Java Programming: Program Design Including Data Structures

5. Classes (continued)
Private: members of class are not accessible outside class
Public: members of class are accessible outside class
Class members: can be methods or variables
Variable members are declared like any other variables
Java Programming: Program Design Including Data Structures

6. Syntax The general syntax for defining a class:
If a member of a class is a named constant, you declare it just like any other named constant
If a member of a class is a variable, you declare it just like any other variable
Java Programming: Program Design Including Data Structures

7. Syntax (continued)
If a member of a class is a method, you define it just like any other method
If a member of a class is a method, it can (directly) access any member of the class—data members and methods
When you write the definition of a method, you can directly access any data member of the class (without passing it as a parameter)
Java Programming: Program Design Including Data Structures

8. Syntax (continued) class Clock: Data Members (Instance Variables):
private int hr; //store hours
private int min; //store minutes
private int sec; //store seconds
Methods:
public void setTime(int hours, int minutes,
int seconds)
public int getHours()
public int getMinutes()
public int getSeconds()
public void printTime()
public void incrementSeconds()
public void incrementMinutes()
public void incrementHours()
public boolean equals(Clock otherClock)
public void makeCopy(Clock otherClock)
public Clock getCopy()
Java Programming: Program Design Including Data Structures

9. Constructors Two types of constructors: With parameters
Without parameters (default constructor)
Java Programming: Program Design Including Data Structures

10. Constructors (continued)
Constructors have the following properties:
The name of a constructor is the same as the name of the class
A constructor has no return type
A class can have more than one constructor
All constructors of a class have the same name
If a class has more than one constructor, any two constructors must have different signatures
Java Programming: Program Design Including Data Structures

11. Constructors (continued)
Constructors are automatically executed when a class object is instantiated
With multiple constructors, which constructor executes depends on the type of values passed to the class object when the class object is instantiated
Java Programming: Program Design Including Data Structures

12. Constructors (continued)
class Clock: Constructors
Default constructor is public Clock()
Constructor with parameters:
public Clock(int hours, int minutes,int seconds)
Java Programming: Program Design Including Data Structures

13. Unified Modeling Language Class Diagrams
Java Programming: Program Design Including Data Structures

14. Variable Declaration and Object Instantiation
General syntax for using the operator new is:
new className() OR
new className(argument1, argument2, ...,
argumentN)
Clock myClock;
Clock yourClock;
myClock = new Clock();
yourClock = new Clock(9, 35, 15);
Java Programming: Program Design Including Data Structures

15. Variable Declaration and Object Instantiation (continued)
Java Programming: Program Design Including Data Structures

16. Accessing Class Members
To access a data member of a class object or method:
referenceVariableName.memberName
Example 8-1
myClock.setTime(5, 2, 30);
myClock.printTime();
yourClock.setTime(x, y, z);
if (myClock.equals(yourClock)) …
Java Programming: Program Design Including Data Structures

17. Assignment Operator: A Precaution
Consider: myClock = yourClock;
Copies the value of the reference variable yourClock into the reference variable myClock
After execution, both variables refer to same object
Java Programming: Program Design Including Data Structures

18. Assignment Operator: A Precaution (continued)
Shallow copying: two or more reference variables of the same type point to the same object
Deep copying: each reference variable refers to its own object
Java Programming: Program Design Including Data Structures

19. The Copy Constructor Executes when an object is instantiated
Initialized using an existing object
Syntax:
public ClassName(ClassName otherObject)
Java Programming: Program Design Including Data Structures

20. Example: class Clock
Java Programming: Program Design Including Data Structures

21. The Method toString Public value-returning method Takes no parameters
Returns address of a String object
Output using print, println, printf methods
Default definition creates String with name of object’s class name followed by hash code of object
System.out.println(myClock);
is:
Java Programming: Program Design Including Data Structures

22. The Modifier static
In the method heading, specifies that the method can be invoked by using the name of the class
If used to declare data member, data member invoked by using the class name
Static data members of class exist even when no object of class type instantiated
Static variables are initialized to their default values
Java Programming: Program Design Including Data Structures

23. The Modifier static (continued)
Example 8-3
public class Illustrate {
private int x;
private static int y;
public static int count;
public Illustrate()
x = 0; }
public Illustrate(int a)
x = a;
Java Programming: Program Design Including Data Structures

24. The Modifier static (continued)
void setX(int a) {
x = a; }
public String toString()
return("x = " + x + ", y = " + y
+ ", count = " + count);
public static void incrementY()
y++;
Illustrate illusObject = new Illustrate();
Illustrate.incrementY();
Illustrate.count++;
Java Programming: Program Design Including Data Structures

25. The Modifier static (continued)
Illustrate illusObject1 = new Illustrate(3);
Illustrate illusObject2 = new Illustrate(5);
Java Programming: Program Design Including Data Structures

26. The Modifier static (continued)
Illustrate.incrementY();
Illustrate.count++;
Java Programming: Program Design Including Data Structures

27. Finalizers Automatically execute when class object goes out of scope
Have no parameters
Only one finalizer per class
Name of finalizer: finalize
Java Programming: Program Design Including Data Structures

28. Accessor and Mutator Methods
Accessor method: A method of a class that only accesses (that is, does not modify) the value(s) of the data member(s)
Mutator method: modifies the value(s) of the data member(s)
Java Programming: Program Design Including Data Structures

29. Creating Packages
You can create packages using a reserved word package
Define the class to be public. (If class is not public, it can only be used within package.)
Choose name for package
Organize package (create subdirectories)
Java Programming: Program Design Including Data Structures

30. Creating Package for class Clock
package jpfpatpd.ch08.clockPackage;
public class Clock {
//put instance variables and methods,
//as before, here }
import jpfpatpd.ch08.clockPackage.Clock;
Java Programming: Program Design Including Data Structures

31. The Reference this Refers to instance variables and methods of a class
Used to implement cascaded method calls
Java Programming: Program Design Including Data Structures

32. Inner Classes Defined within other classes
Can be either a complete class definition or an anonymous inner class definition
Used to handle events
Java Programming: Program Design Including Data Structures

33. Abstract Data Type
A data type that specifies the logical properties without the implementation details
Java Programming: Program Design Including Data Structures

34. Programming Example: Candy Machine (Problem Statement)
A new candy machine is bought for the gym, but it is not working properly. The machine sells candies, chips, gum, and cookies. In this programming example, we will write a program to create a Java application program for this candy machine so that it can be put into operation. We will divide this program in two parts. In the first part, we will design a non-GUI application program. In the second part, we will design an application program that will create a GUI, as described in the second part.
Java Programming: Program Design Including Data Structures

35. Programming Example: Candy Machine (Problem Statement continued)
The non-GUI application program should do the following:
1. Show the customer the different products sold
2. Let the customer make the selection
3. Show the customer the cost of the item selected
4. Accept money from the customer
5. Release the item
Java Programming: Program Design Including Data Structures

36. Programming Example: Candy Machine (Input and Output)
Input: The item selection and the cost of the item
Output: The selected item
Java Programming: Program Design Including Data Structures

37. Programming Example: Candy Machine
Components:
Cash register
Dispenser
Machine
Java Programming: Program Design Including Data Structures

38. Programming Example: Candy Machine (continued)
Java Programming: Program Design Including Data Structures

39. Programming Example: Candy Machine (continued)
Java Programming: Program Design Including Data Structures

40. Programming Example: Candy Machine (continued)
Java Programming: Program Design Including Data Structures

41. Programming Example: Candy Machine (continued)
Java Programming: Program Design Including Data Structures

42. Programming Example: Candy Machine (continued)
Java Programming: Program Design Including Data Structures

43. Programming Example: Candy Machine (continued)
Java Programming: Program Design Including Data Structures

44. Chapter Summary Creating classes Members of a class:
private
protected
public
static
Implementing classes
Various operations on classes
Java Programming: Program Design Including Data Structures

45. Chapter Summary (continued)
Constructors
Finalizers
Method toString
Abstract data types
Java Programming: Program Design Including Data Structures