1. Chapter 8 Classes User-Defined Classes and ADTs
class: reserved word; collection of a fixed number of components
Components: members of a class
Members accessed by name
Class categories/modifiers
private
protected
public

2. Classes 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 declared like any other variables

3. Syntax The general syntax for defining a class is:
modifier(s) class ClassIdentifier modifier(s) {
classMembers }
The general syntax for using the operator new is:
new className() //Line 1 OR
new className(argument1, argument2, ..., argumentN) //Line 2

4. Classes
The syntax to access a data member of a class object or method is:
referenceVariableName.memberName
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

5. Constructors
Guarantee that data members are initialized when object is declared
Automatically execute when class object created
Name of constructor is name of class
More than one constructor can be present in one class
Default constructor: constructor without parameters

6. The Copy Constructor Executes when an object is instantiated
Initialized using an existing object
Syntax:
public ClassName(ClassName otherObject)

7. UML Diagram

8. UML Diagram Top box: name of class
Middle box: data members and their data types
Bottom box: member methods’ names, parameter list, return type of method
+ means public method
- means private method
# means protected method

9. Example: class Clock myClock = new Clock();
yourClock = new Clock(9,35,15);

10. Example: class Clock

11. Example: class Clock

12. The Method toString public value-returning method Takes no parameters
Returns address of String object
Output using print and println methods
Default definition creates String with name of object’s class name followed by hash code of object

13. 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

14. static Data Members of a Class
Illustrate illusObject1 = new Illustrate(3);
Illustrate illusObject2 = new Illustrate(5);

15. Finalizers Automatically execute when class object goes out of scope
Have no parameters
Only one finalizer per class
Name of finalizer: finalize

16. Creating Packages You can create packages using 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)

17. 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;

18. The Reference this Refers to instance variables and methods of a class
Used to implement cascaded method calls

19. Inner Classes Defined within other classes
Can be either a complete class definition or anonymous inner class definition
Used to handle events

20. Abstract Data Types Definition:
A data type that specifies the logical properties without the implementation details