The document discusses class definitions, inheritance, abstract classes, and interfaces in Java. It provides examples of defining classes with variables and methods, creating objects, and using inheritance, abstract classes, and interfaces. Some key points covered include: - Classes define data (variables) and behavior (methods) and can be instantiated with the new operator to create objects. - Inheritance allows classes to extend existing classes, inheriting their variables and methods while also adding new ones. Derived classes can override methods from the base class. - Abstract classes cannot be instantiated but provide common functionality to derived classes through abstract and non-abstract methods. Derived classes must implement abstract methods. - Interfaces define common behaviors (public

1. Class Definition. Inheritance
Abstract Class & Interfaces

2. Class Definition

3. •
•
•
• Scanner keyboard;
•
• Keyboard = new String();
•
• keyboard.nextInt();

4. • class data
• variables. methods
int a;
int b;
float c;
a = 1;
b = 2;
c = 4.5;
a = 6;
b = 4;
c = 8.6;
Object 1
Object 2
new
new
Class

5. variables
method(s)
members

6. •
• Date object1;
• new :
• object1 = new Date();
•
• Date object1 = new Date();
• Date object2 = new Date();
String month;
int day;
int year;
writeOutput()
month = May;
day = 6;
year = 1994;
month = October;
day = 25;
year = 1990;
new
new
Date

7. Demo.java

8. •
•
•
Heading
body
最重要的是這個回傳值宣告
當method動作最後有
return ___;
取決於回傳了什麼東西
回傳 int 就要寫 int
回傳 String 就要寫 String
如沒有回傳 也要寫 void

9. •
• object1.month;
• object2.day;
•
• object1.writeOutput();
String month;
int day;
int year;
writeOutput();
month = May;
day = 6;
year = 1994;
month = October;
day = 25;
year = 1990;
object1
object2
new
new
Demo

10. •
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12. • main void
• main
public static void main (String[] args)
{
……
}

13. •
•
•
public void method_a()
{
int a;
…
}
public void method_b()
{
int a;
…
}

14. •

15. •
public class Date
{
String month;
int day;
int year;
public void setDate(String month, int day, int year)
{
this.month = month;
this.day = day;
this.year = year;
}
}

16. Q & A ?

17. Information Hiding & Encapsulation
&

18. •
•
private

19. private
DateTry date = new Demo( );
(1) date.month = “January”;
(2) date.day = 1;
(3) date.year = 2008;
(4) date.writeOutput( );
(5) date.getDay( );
Another class

20. private
public
, private
methods

21. •
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•
•
•
•
int getA( ) { return a; }
// Accessor method
void setA(int p) { a = p; }
// Mutator method
int getB( ) { return b; }
// Accessor method
void setB(int p) { b = p; }
// Mutator method
float getC( ) { return c; }
// Accessor method
void setC(float p) { c = p; }
// Mutator method
private int a;
private int b;
private float c;
class

22. •
•

23. •
•
public int getDate( )
{
}
public String getDate( )
{
}

24. Constructors

25. •
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26. •
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• false
• null
• zero

27. Overloaded

28. •
• Date object1 = new Date(5, 6, 1990);
• Date object2 = new Date(May, 6, 1990);
• Date object3 = new Date(1994);
•
• object1.Date()

29. Q & A ?

30. Static Type

31. •
•
(1) Round.area(radius)
(2) Round.volume(radius)
Round r = new Round();
(3) r.volume(radius)

32. •
•
void method1( )
{
B obj = new B( );
myobj.method2( );
}
void static method2( )
{
B.method1( );
}
void static method3( )
{
this.method1( )
}
void static method1( )
{
}
void method2( )
{
}

33. •
•
•
•
• Private static int myStaticVariable;

34. •
static int a;
int b;
Class myClass
b = 10; b = 5; b = 3; b = 1;
obj1 obj2 obj3 obj4

35. • private
•
• final
• public
• public static final int BIRTH_YEAR = 1994;
•
• int year = ClassName.BIRTH_YEAR;

36. Q & A ?

37. Inheritance

38. •
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•

39. •
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41. •
• public class HourlyEmployee extends Employee

42. String name;
int hireDate;
int hours;
int Salaryrate;
Employee HourlyEmployee
Inherit

43. •
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•
•
•
•

44. Override

45. •
•
•
String name;
int hireDate;
public int getSalary()
{
definition
}
int hours;
int Salaryrate;
public int getSalary()
{
definition
}
Employee HourlyEmployee
Inherit

46. •
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47. •
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48. • private void doSomething()
• public void doSomething()
• public void doSomething()
• private void doSomething()
Override OK
Override WRONG!

49. • final
•
• final
•
•

50. •
•
• super ( )
public derivedClass(int p1, int p2, double p3)
{
super(p1, p2);
instanceVariable = p3;
}
Constructor method();
Method1();
Constructor method();
super()
Base Class
Derived Class

51. •
•
• this
public ClassName(type1 param1, type2 param2)
{
…
}
public ClassName()
{
this(argument1, argument2);
}

52. public class Employee
{
private String name;
private Date hireDate;
public Employee( )
{
}
public Employee(String theName, Date theDate)
{
}
public Employee(Employee originalObject)
{
}
}
public class HourlyEmployee extends Employee
{
private double wageRate;
private double hours;
public HourlyEmployee( )
{
this(“No name”, new Date(“January”, 1, 1000), 0, 0);
}
public HourlyEmployee(String theName, Date theDate,
double theWageRate, double theHours)
{
}
}

53. •
•
A class obj1
B class obj2
C class obj3
A obj1 = new A( );
B obj2 = new B( );
C obj3 = new C( );
obj1 = obj2; (1)
obj1 = obj3; (2)
obj2 = obj3; (3)
obj3 = obj1; (4)

54. •
private methodA()
{
…
}
public methodB()
{
methodA();
}
In Base Class
Invoke in derived class

55. •
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• getClass()
• object1.getClass() == object2.getClass()

56. Q & A ?

57. Abstract Class

58. •
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• Late Binding
• Dynamic Binding

59. •
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• final. private. static
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60. Employee obj1 = new Employee( );
HourlyEmployee obj2 = new HourlyEmployee( );
obj1 = obj2;
obj1.m1();
Employee obj1 = new Employee( );
HourlyEmployee obj2 = new HourlyEmployee( );
obj1.m1();
Employee & HourlyEmployee m1()
obj1.m1() m1 method

61. •
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•

62. •
• private

63. public abstract class Employee
{
private String name;
private Date hireDate;
public abstract double getPay( );
}
public class HourlyEmployee extends Employee
{
private double payRate;
private double hours;
public double getPay( )
{
return payRate * hours;
}
}
public static void main(String args[])
{
Employee tony = new Employee( ); ERROR!!
HourlyEmployee joe = new HourlyEmployee( );
}
public class SalaryEmployee extends Employee
{
private double salary;
private double hours;
public double getPay( )
{
return salary / 12;
}
}

64. Q & A ?

65. Interface

66. •
•
•
• public

68. •
• class className extends baseclass implements Interface1, Interface2
•
•
• , methods (Override)
• , methods,
• , methods

69. •
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• public. static & final

70. Q & A ?