Chapter 9: Objects and Classes

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3 Fortran Algol Pascal Modula-2 BCPL C Simula SmallTalk C++ Ada Java C#

4 C Fortran

5 5.1

8 message A B

9 5.2

11 1 class Vehicle subclass Car object mycar

12 public class Vehicle extends Object{ public int WheelNum = 4; //...// } import Vehicle; public class Car extends Vehicle{ public int DoorNum = 4 ; public String EngineType = "V6" ;...// } import java.io.*; import Car; public class Me{ public static void main(string args[]){ Car mycar = new Car(); System.out.printlin(" "+mycar.wheelnum); System.out.printlin(" "+mycar.enginetype); } }

13 Circle radius Graphical notation for classes findarea new Circle() new Circle() circle1: Circle radius = 2... circlen: Circle radius = 5 Graphical notation for objects

14 2 class Circle { double radius = 1.0; } double findarea() { return radius*radius* ; }

15 5.3

16 class Car { int color_number; int door_number; int speed; } void brake() { } void speedup() { }; void slowdown() { }

17 5.4 ClassName objectname; Example: Car mycar; Circle mycircle; objectname = new ClassName(); Example: mycar = new Car(); mycircle = new Circle();

18 ClassName objectname = new ClassName(); Example: Car mycar = new Car(); Circle mycircle = new Circle();

19 5.5 Primitive type int i = 1 i 1 Object type Circle c c reference Created using new Circle(5) c: Circle radius = 5

20 Primitive type assignment i = j Object type assignment c1 = c2 Before: After: Before: After: i 1 i 2 c1 c1 j 2 j 2 c2 c2 c1: Circle c2: Circle radius = 5 radius = 9

21 Primitive type assignment i = j Object type assignment c1 = c2 Before: After: Before: After: i 1 i 2 c1 c1 j 2 j 2 c2 c2 c1: Circle radius = 5 c2: Circle radius = 9

22 5.6 static final static

23 Notation: +: public variables or methods -: private variables or methods underline: static variables or metods Memory radius is an instance variable, and numofobjects is a class variable Circle -radius -numofobjects +getradius +setradius +getnumofobjects +findarea instantiate instantiate circle1:circle -radius = 1 -numofobjects = 2 circle2:circle -radius = 5 -numofobjects = 2 1 radius 2 5 radius numofobjects

24 Example numofobjects Circle Circle private double radius private static int numofobjects public double getradius( ) public void setradius(double newradius) public static int getnumofobjects( ) public double findarea( ) TestInstanceAndClassVariable Run

25 5.7 : objectname.data mycircle.radius : objectname.method mycircle.findarea()

26 Example 5.1 Circle TestCircle Run

27 5.8 void new

28 5.8 Circle(double r) { radius = r; } Circle() { radius = 1.0; } mycircle = new Circle(5.0);

29 Example 5.2 Circle TestCircleWithConstructors Run

30 5.9 Example 5.3 TestPassingObject Run

31 mycircle n main printareas n mycircle main 5 mycircle Circle radius=1 printareas times c 5

32 5.10 Java public. private. getter and setter

33 Example 5.4 private Circle getradius and setradius TestCircleWithPrivateModifier Run

34 5.11 Java { { }}

36 class A{ int x; int f() { int a=5; x=a; // x } int g() { int y; y=a;// aga } }

37 class Tom{ int x=98,y; void f() { int x=3; y=x; //y 3 98 } }

38 5.12 this super this this this super Java super

39 Example 5.6 this super class A { int a; A(int new_value) { a = new_value; } } class B extends A { int b, c; B() { this(2, 3); } B(int new_b, int new_c) { super(1); b = new_b; c = new_c; } }

40 class Demo { public static void main(string[] args) ) { B obj_b = new B(); System.out.println("a= = "+obj_b.a + "; b= "+obj_b.b + "; c= "+ obj_b.c); } } a= 1; b= 2; c= 3

42 Student 5.60 * Course Faculty

43 Student 5.60 * Course Faculty

44 Student 5.60 * Course Faculty

45 Student 5.60 * Course Faculty

46 Student * Course Faculty

47 Student * Course Faculty

48 (has-a) (part-of) (own) (employedby) Magazine * 1 Publisher * * Consultant

49 (has-a) (part-of) (own) (employedby) Magazine * 1 Publisher * * Consultant

50 (is-a) Person Student Faculty

52 Example Name 1 Borrower Address 1 Mortgage

53 Example 5.6 The following is a test program that uses the classes Name, Address, Borrower, and Mortgage. BorrowMortgage Run

54 5.15 Java API and Core Java classes java.lang JavaObject String Math Number SystemJava java.awt java.applet applet

55 5.15 Java API and Core Java classes, cont. java.io java.util java.net

56 5.15 Java API and Core Java classes, cont. java.awt.image bitmap. java.awt.peer GUI Others: java.sql java.rmi

58 5.16 The String Class Javajava.lang String "student100", "China" C

59 5.16 The String Class String String s; = new String = s = new String ( "student" ); s = "student" String s = new String ( "student" ); String s = "student

60 5.16 The String Class String tom = "my name is tom"; String jane = "my name is jane"; tom.equals(jane) false String s = " I am"; String s2 = "a Chinese"; String s3, s4; s3 = s + s2; s4 = s + 24; 24

61 5.16 The String Class String s = "I am a Chinese"; String subs; subs = s.substring (7);//Chinese subs = s.substring (0,8);//I am a C length() String s = "student"; int len=s.length(); endindex beginindex, endindex

62 5.16 The String Class String String s = "I am a Chinese"; s.indexof("chinese" );// 7 s.indexof('a'); //2 Do not use message[0] s.charat(index) index 0 s.length()-1

63 5.17 The StringBuffer Class StringBuffer String.. StringBuffer String..

64 StringBuffer public StringBuffer() 16. public StringBuffer(int length) length. public StringBuffer(String str) string string 16.

65 StringBuffer StringBuffer StringBuffer strbuf = new StringBuffer(); strbuf.append("welcome"); strbuf.append(' to Java'); sb1.append( this is a book. ); sb1.insert(6,30); // int,char,double,string sb1.setcharat(0, a );

66 5.18 The StringTokenizer Class Constructors StringTokenizer(String s, String delim, boolean returntokens) delims StringTokenizer returntokens true

67 Class Constructors StringTokenizer(String s, String delim) delims StringTokenizer StringTokenizer(String s) s StringTokenizer

68 The StringTokenizer Class Methods boolean hasmoretokens() true String nexttoken() String nexttoken(string delim) delim public int counttokens() StringTokenizer

69 ? this

Microsoft Word - 第3章.doc

Microsoft Word - 第3章.doc Java C++ Pascal C# C# if if if for while do while foreach while do while C# 3.1.1 ; 3-1 ischeck Test() While ischeck while static bool ischeck = true; public static void Test() while (ischeck) ; ischeck