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CS 200 - Programming I: Classes
Marc Renault
Department of Computer SciencesUniversity of Wisconsin – Madison
Fall 2019TopHat Sec 3 (1:20 PM) Join Code: 682357TopHat Sec 4 (3:30 PM) Join Code: 296444
Classes UML
Classes
Classes UML
Class
Defining ClassesClasses provide a way of defining new types.They are data structures that:
can group member variables.can group member methods.
publicmembers are accessible outside the class.privatemembers are only accessible inside the class.
Creating instances of classesMyClass varName = new MyClass(arg1, ...)
Creating instances of your own classes work just as thepredefined Java classes.
1/23
Classes UML
Class
Defining ClassesClasses provide a way of defining new types.They are data structures that:
can group member variables.can group member methods.
publicmembers are accessible outside the class.privatemembers are only accessible inside the class.
Creating instances of classesMyClass varName = new MyClass(arg1, ...)
Creating instances of your own classes work just as thepredefined Java classes.
1/23
Classes UML
Class
Defining ClassesClasses provide a way of defining new types.They are data structures that:
can group member variables.can group member methods.
publicmembers are accessible outside the class.privatemembers are only accessible inside the class.
Creating instances of classesMyClass varName = new MyClass(arg1, ...)
Creating instances of your own classes work just as thepredefined Java classes.
1/23
Classes UML
TopHat Question 1What is the output when executed?
public class MyClass {
public int a;
public MyClass () {a = 5;
}
public static void main(String [] args) {MyClass b = new MyClass ();b.a = 10;System.out.print(b.a);
}}
2/23
Classes UML
TopHat Question 2What is the output when executed?
public class MyClassBis {
private int a;
public MyClassBis () {a = 5;
}
public static void main(String [] args) {MyClassBis b = new MyClassBis ();b.a = 10;System.out.print(b.a);
}}
3/23
Classes UML
TopHat Question 3What is the output when UseMyClass is executed?public class UseMyClass {
public static void main(String [] args) {MyClass b = new MyClass ();b.a = 10;System.out.print(b.a);
}
}
public class MyClass {
public int a;
public MyClass () {a = 5;
}
public static void main(String [] args) {MyClass b = new MyClass ();b.a = 10;System.out.print(b.a);
}}
4/23
Classes UML
TopHat Question 4What is the output when UseMyClassBis is executed?public class UseMyClassBis {
public static void main(String [] args) {MyClassBis b = new MyClassBis ();b.a = 10;System.out.print(b.a);
}
}
public class MyClassBis {
private int a;
public MyClassBis () {a = 5;
}
public static void main(String [] args) {MyClassBis b = new MyClassBis ();b.a = 10;System.out.print(b.a);
}}
5/23
Classes UML
Class Interface
Class InterfacePublic view of the class.publicmethods and members that can be accessed fromoutside.
Good Practice: Keep Things privateCode smell: indecent exposure.private unless reason to make public.Encapsulation is one of the fundamental principals inobject-oriented programming (OOP).
6/23
Classes UML
Class Interface
Class InterfacePublic view of the class.publicmethods and members that can be accessed fromoutside.
Good Practice: Keep Things privateCode smell: indecent exposure.private unless reason to make public.Encapsulation is one of the fundamental principals inobject-oriented programming (OOP).
6/23
Classes UML
Member Variables
public class HockeyPlayer {
private String name;private int goals;private int assists;private int gamesPlayed;private double toi;private double penaltyMin;
public HockeyPlayer () {name = "";initMemberVars ();
}
public HockeyPlayer(String name) {this.name = name;initMemberVars ();
}
private void initMemberVars () {goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
}
public String getName () {return name;
}
public void setName(String name) {this.name = name;
}
public int getGoals () {return goals;
}
public int getAssists () {return assists;
}
public int getPoints () {return goals + assists;
}
public int getGamesPlayed () {return gamesPlayed;
}
public double getToi () {return toi;
}
public double getPenaltyMin () {return penaltyMin;
}
public void addPenaltyTime(double time) {penaltyMin += time;
}
public void addGoal () {goals ++;
}
public void addAssist () {assists ++;
}
public void addToi(double time) {toi += time;
}
public void addGamePlayed () {gamesPlayed ++;
}
}
FieldsFields are membervariables.Non-static membervariables are instancevariables.
PropertiesFields that can be set bythose using the class.
Default ValuesUninitialized membervariables are given defaultvalues.
7/23
Classes UML
Member Variables
public class HockeyPlayer {
private String name;private int goals;private int assists;private int gamesPlayed;private double toi;private double penaltyMin;
public HockeyPlayer () {name = "";initMemberVars ();
}
public HockeyPlayer(String name) {this.name = name;initMemberVars ();
}
private void initMemberVars () {goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
}
public String getName () {return name;
}
public void setName(String name) {this.name = name;
}
public int getGoals () {return goals;
}
public int getAssists () {return assists;
}
public int getPoints () {return goals + assists;
}
public int getGamesPlayed () {return gamesPlayed;
}
public double getToi () {return toi;
}
public double getPenaltyMin () {return penaltyMin;
}
public void addPenaltyTime(double time) {penaltyMin += time;
}
public void addGoal () {goals ++;
}
public void addAssist () {assists ++;
}
public void addToi(double time) {toi += time;
}
public void addGamePlayed () {gamesPlayed ++;
}
}
FieldsFields are membervariables.Non-static membervariables are instancevariables.
PropertiesFields that can be set bythose using the class.
Default ValuesUninitialized membervariables are given defaultvalues.
7/23
Classes UML
Member Variables
public class HockeyPlayer {
private String name;private int goals;private int assists;private int gamesPlayed;private double toi;private double penaltyMin;
public HockeyPlayer () {name = "";initMemberVars ();
}
public HockeyPlayer(String name) {this.name = name;initMemberVars ();
}
private void initMemberVars () {goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
}
public String getName () {return name;
}
public void setName(String name) {this.name = name;
}
public int getGoals () {return goals;
}
public int getAssists () {return assists;
}
public int getPoints () {return goals + assists;
}
public int getGamesPlayed () {return gamesPlayed;
}
public double getToi () {return toi;
}
public double getPenaltyMin () {return penaltyMin;
}
public void addPenaltyTime(double time) {penaltyMin += time;
}
public void addGoal () {goals ++;
}
public void addAssist () {assists ++;
}
public void addToi(double time) {toi += time;
}
public void addGamePlayed () {gamesPlayed ++;
}
}
FieldsFields are membervariables.Non-static membervariables are instancevariables.
PropertiesFields that can be set bythose using the class.
Default ValuesUninitialized membervariables are given defaultvalues.
7/23
Classes UML
Member Instance Methodsprivate void initMemberVars () {
goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
}
public String getName () {return name;
}
public void setName(String name) {this.name = name;
}
public int getGoals () {return goals;
}
public int getAssists () {return assists;
}
public int getPoints () {return goals + assists;
Instance MethodsNon-static methods whosebehaviour depends on theparticular object instance.
8/23
Classes UML
Constructorspublic class HockeyPlayer {
private String name;private int goals;private int assists;private int gamesPlayed;private double toi;private double penaltyMin;
public HockeyPlayer () {name = "";initMemberVars ();
}
public HockeyPlayer(String name) {this.name = name;initMemberVars ();
}
private void initMemberVars () {goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
ConstructorSpecial method with noreturn type.Same name as the class.Called when creating aninstance.Can be overloaded.
Default ConstructorIf no constructor isdefined, Java provides adefault constructor with noparameters.It is good practice to definea constructor.
9/23
Classes UML
Constructorspublic class HockeyPlayer {
private String name;private int goals;private int assists;private int gamesPlayed;private double toi;private double penaltyMin;
public HockeyPlayer () {name = "";initMemberVars ();
}
public HockeyPlayer(String name) {this.name = name;initMemberVars ();
}
private void initMemberVars () {goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
ConstructorSpecial method with noreturn type.Same name as the class.Called when creating aninstance.Can be overloaded.
Default ConstructorIf no constructor isdefined, Java provides adefault constructor with noparameters.It is good practice to definea constructor.
9/23
Classes UML
What is this?
public HockeyPlayer(String name) {this.name = name;initMemberVars ();
}public void setName(String name) {
this.name = name;}
this keywordthis is a reference to the object (or the current instance).The object is an implicit parameter of all instance methods.
10/23
Classes UML
What is this?this keyword
this is a reference to the object (or the current instance).The object is an implicit parameter of all instance methods.Can also be used to call other constructors:
public HockeyPlayer () {name = "";goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
}
public HockeyPlayer(String name) {this ();this.name = name;
}10/23
Classes UML
Mutators, Accessors, and Helpersprivate void initMemberVars () {
goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
}
public int getPoints () {return goals + assists;
}
public void addGoal () {goals ++;
}
Helpersprivatemethod usedwithin the class.
AccessorsMethods that access themember variables withoutchanging them.
MutatorsMethods that change themember variables.
11/23
Classes UML
Mutators, Accessors, and Helpersprivate void initMemberVars () {
goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
}
public int getPoints () {return goals + assists;
}
public void addGoal () {goals ++;
}
Helpersprivatemethod usedwithin the class.
AccessorsMethods that access themember variables withoutchanging them.
MutatorsMethods that change themember variables.
11/23
Classes UML
Mutators, Accessors, and Helpersprivate void initMemberVars () {
goals = 0;assists = 0;gamesPlayed = 0;toi = 0.0;penaltyMin = 0.0;
}
public int getPoints () {return goals + assists;
}
public void addGoal () {goals ++;
}
Helpersprivatemethod usedwithin the class.
AccessorsMethods that access themember variables withoutchanging them.
MutatorsMethods that change themember variables.
11/23
Classes UML
Getters and Setterspublic String getName () {
return name;}
public void setName(String name) {this.name = name;
}
GetterAccessor method thatretrieves a property.
SetterMutator method to changea property.
Best PracticeGood for properties.Violates OOP encapsulation when used for all fields.Why getter and setter methods are evilhttps://www.javaworld.com/article/2073723/core-java/why-getter-and-setter-methods-are-evil.html
12/23
Classes UML
Getters and Setterspublic String getName () {
return name;}
public void setName(String name) {this.name = name;
}
GetterAccessor method thatretrieves a property.
SetterMutator method to changea property.
Best PracticeGood for properties.Violates OOP encapsulation when used for all fields.Why getter and setter methods are evilhttps://www.javaworld.com/article/2073723/core-java/why-getter-and-setter-methods-are-evil.html
12/23
Classes UML
Getters and Setterspublic String getName () {
return name;}
public void setName(String name) {this.name = name;
}
GetterAccessor method thatretrieves a property.
SetterMutator method to changea property.
Best PracticeGood for properties.Violates OOP encapsulation when used for all fields.Why getter and setter methods are evilhttps://www.javaworld.com/article/2073723/core-java/why-getter-and-setter-methods-are-evil.html 12/23
Classes UML
TopHat Question 5
What is the output?
public class UseHockeyPlayer {
public static void main(String [] args) {HockeyPlayer h = new HockeyPlayer("Auston Matthews");System.out.print(h);
}
}
a. Auston Matthewsb. HockeyPlayer@5e265ba4
13/23
Classes UML
TopHat Question 6What is the output when executed?
public class SimpleClass {
public int x;
public SimpleClass(int x) {this.x = x;
}
public String toString () {return "" + x;
}
public static void main(String [] args) {SimpleClass a = new SimpleClass (10);SimpleClass b = new SimpleClass (10);b.x = 20;System.out.print(a + " " + b);
}}
14/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
s
Heap
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
s
y: 0
StaticA:x: 0
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
s
y: 0
StaticA:x: 0
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
s
y: 1
StaticA:x: 0
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
s
y: 1
StaticA:x: 0
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
s
y: 1
StaticA:x: 2
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
st
y: 1
StaticA:x: 2
y: 0
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;StaticA t
= new StaticA ();
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
st
y: 1
StaticA:x: 2
y: 0
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;StaticA t
= new StaticA ();t.x = 3;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
st
y: 1
StaticA:x: 3
y: 0
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;StaticA t
= new StaticA ();t.x = 3;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
st
y: 1
StaticA:x: 3
y: 0
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;StaticA t
= new StaticA ();t.x = 3;t.y = 4;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
st
y: 1
StaticA:x: 3
y: 4
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;StaticA t
= new StaticA ();t.x = 3;t.y = 4;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
st
y: 1
StaticA:x: 3
y: 4
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;StaticA t
= new StaticA ();t.x = 3;t.y = 4;StaticA.x = 5;
15/23
Classes UML
Static Member VariablesStatic Member Variables
Class variablesStored in a special part of the heap.
Stack
st
y: 1
StaticA:x: 5
y: 4
Heap class StaticA {public static int x;public int y;
}public class StaticEx {
public staticvoid main(String [] args){
StaticA s= new StaticA ();
s.y = 1;s.x = 2;StaticA t
= new StaticA ();t.x = 3;t.y = 4;StaticA.x = 5;
15/23
Classes UML
TopHat Question 7
What is the output when executed?
public class SimpleStaticClass {
public static int x = 10;
public String toString () {return "" + x;
}
public static void main(String [] args) {SimpleStaticClass a = new SimpleStaticClass ();SimpleStaticClass b = new SimpleStaticClass ();b.x = 20;System.out.print(a + " " + b);
}}
16/23
Classes UML
TopHat Question 8
What is the output?
public class StaticEx2 {
private static int i = 0;
public static int f() {return ++i;
}
public static void main(String [] args) {System.out.print(f() + " " + f() + " " + f());
}
}
17/23
Classes UML
UML
Classes UML
Unified Modeling Language (UML)UML
A modeling language used in software engineering.A visual way to describe a software system.
Some UML DiagramsUse Case DiagramClass DiagramInstance Diagram
UML Resourceshttp://agilemodeling.com/
https://www.uml-diagrams.org/
Online Drawing Tool:http://www.umlet.com/umletino/umletino.html
18/23
Classes UML
Unified Modeling Language (UML)UML
A modeling language used in software engineering.A visual way to describe a software system.
Some UML DiagramsUse Case DiagramClass DiagramInstance Diagram
UML Resourceshttp://agilemodeling.com/
https://www.uml-diagrams.org/
Online Drawing Tool:http://www.umlet.com/umletino/umletino.html
18/23
Classes UML
Unified Modeling Language (UML)UML
A modeling language used in software engineering.A visual way to describe a software system.
Some UML DiagramsUse Case DiagramClass DiagramInstance Diagram
UML Resourceshttp://agilemodeling.com/
https://www.uml-diagrams.org/
Online Drawing Tool:http://www.umlet.com/umletino/umletino.html
18/23
Classes UML
Use Case DiagramBP1 MastermindBP1 Mastermind
Choose the random seed
Enter a guess
Choose to play againPlayer
Use Case DiagramSimple graphical representation of the system.Describes how the external actors (users) interact with thesystem.
19/23
Classes UML
Class Diagram
5..* 0..1
1..*
0..1 2..*
0..1
HockeyPlayer
name: Stringgoals: intassists: int
addGoal()setName(name: String)
Goalie
saves: intshots: int
getSavePct(): double
HockeyTeam
HockeyLeague
plays for I
plays f
or Ibelongs to
I
Class DiagramDescribes the structure of the system at the class level.
20/23
Classes UML
Instance DiagramHockeyLeague
name = NHL
wildHockeyTeam
name =Wildlocation = Minnesota
hawksHockeyTeam
name = Blackhawkslocation = Chicago
HockeyTeam
name = Maple Leafslocation = Toronto
HockeyPlayer
name = Auston MatthewsGoals = 10Assists = 6
Goalie
name = Frederik Andersensaves = 505shots = 540
Object / Instance DiagramDescribes the state of the system at the object level at agiven instance in time. 21/23
Classes UML
UML ExerciseDraw the use-case and class diagrams for the following UsedCar Sale system.
Vehicles are identified by a VIN, colour, engine type, gastype, and transmission type.Each vehicle has certificate recording the number ofkilometres, date of last inspection, number of accidents.Vehicles are sub-divided into:
cars, noting the number of passengerstrucks, noting the weight classvans, noting the number of passenger and the weight class
Clients are registered, indicating their name, address andphone number.Clients can search for and buy the used vehicles.Clients sign purchase contracts indicating the purchasedate, sale price, number of payments.
22/23
Classes UML
Further Reading
COMP SCI 200: Programming IzyBooks.com, 2015.zyBook code:WISCCOMPSCI200Fall2019
Chapter 12. Creating ClassesChapter 13. More Classes
23/23
Appendix References
Appendix
Appendix References
References
Appendix References
Image Sources I
https://brand.wisc.edu/web/logos/
http://www.zybooks.com/
24/23
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