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The 10 th and 11 th tutoring session Fall, 2012. What is a class, what is an object and why we need classes How to create objects What is a instance method and what is a class method How to create and use methods . Haidong Xue. 5:30pm—8:30pm 10/9/2012 and 10/10/2012 . CSc2310 Tutoring

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the 10 th and 11 th tutoring session fall 2012

The 10th and 11th tutoring sessionFall, 2012

  • What is a class, what is an object and why we need classes
  • How to create objects
  • What is a instance method and what is a class method
  • How to create and use methods

HaidongXue

5:30pm—8:30pm

10/9/2012 and 10/10/2012

slide2

CSc2310 Tutoring

  • Time: 5:30pm-8:30pm
  • Tutor: HaidongXue
  • Website:

http://www.cs.gsu.edu/~hxue1/csc2310_Tutoring/index.html

There are 2 sections:

1. Review

  • What is a class, what is an object and why we need classes
  • How to create objects
  • What is a instance method and what is a class method
  • How to create and use methods

2. Q&A

  • Answer your questions about java programming
class and object
Class and Object
  • What does a program do?
    • Manipulate data
  • There are many ways to organize data in a program, and a very convenient and popular way is Object Oriented, i.e.: using objects to organize data
  • Let’s set the tutoring room as a example
slide4

Assuming in this tutoring room, we have:

A student

Elena

A tutor

A student

Haydon

Robert

  • What are the data we have here?
  • What are the actions on those data?

A student

Kevin

slide5

Data and actions on data:

  • Data:
  • Name: Elena
  • Java Level: 100
  • Data:
  • Name: Haydon
  • Java Level: 30000
  • Teaching Experience: 2000

Elena

  • Data:
  • Name: Robert
  • Java Level: 120

Haydon

Robert

We can use 4 objects to organize all the data here.

To avoid creating the variables for students 3 times, we can use classes

  • Data:
  • Name: Kevin
  • Java Level: 102

Kevin

slide6

Student Class

Tutor Class

  • Data:
  • Name: Elena
  • Java Level: 100
  • Data:
  • Name: Haydon
  • Java Level: 30000
  • Teaching Experience: 2000

Elena

  • Data:
  • Name: Robert
  • Java Level: 120

Haydon

Robert

  • By name, “class” means a type of objects
  • Thereby, we can divide the objects here into 2 classes: Student and Tutor
  • Then, we only need to define 1 student class and 1 tutor class
  • Data:
  • Name: Kevin
  • Java Level: 102

Kevin

slide7

Data:

  • Name: Elena
  • Java Level: 100
  • Data:
  • Name: Haydon
  • Java Level: 30000
  • Teaching Experience: 2000

Elena

Haydon

  • Data:
  • Name: Robert
  • Java Level: 120

class Student{

String name;

intjavaLevel;

}

Robert

class Tutor{

String name;

intjavaLevel;

}

  • Data:
  • Name: Kevin
  • Java Level: 102

Kevin

How to initialize those data for each object?

Using Constructors

constructors
Constructors
  • A method of a class, with the same name as the class name
  • With no return type
  • They are automatically called when creating a object
slide9

Data:

  • Name: Elena
  • Java Level: 100
  • Data:
  • Name: Haydon
  • Java Level: 30000
  • Teaching Experience: 2000

Elena

Haydon

  • Data:
  • Name: Robert
  • Java Level: 120

class Student{

String name;

intjavaLevel;

public Student( String n, int l ){

name=n; javaLevel=l;

}

}

Robert

constructor

  • Data:
  • Name: Kevin
  • Java Level: 102

class Tutor{

String name;

intjavaLevel;

intteachingExp;

public Tutor( String n, intl, intexp){

name=n; javaLevel=l; teachingExp=exp;

}

}

Kevin

constructor

slide10

Data:

  • Name: Elena
  • Java Level: 100
  • Data:
  • Name: Haydon
  • Java Level: 30000
  • Teaching Experience: 2000

Elena

Haydon

class Student{

String name;

intjavaLevel;

public Student( String n, int l ){

name=n; javaLevel=l;

}

}

  • Data:
  • Name: Robert
  • Java Level: 120

Robert

class Tutor{

String name;

intjavaLevel;

intteachingExp;

public Tutor( String n, intl, intexp){

name=n; javaLevel=l; teachingExp=exp;

}

}

  • Data:
  • Name: Kevin
  • Java Level: 102

Kevin

To create the objects in this tutoring room:

Student elena= new Student(“Elena”, 100);

Student robert= new Student(“Robert”, 120);

Student kevin= new Student(“Kevin”, 102);

Tutor haydon= new Tutor(“Haydon”, 30000, 2000);

create objects

methods
Methods
  • Methods are used to represent the actions on data
  • E.g.: A student here may learn java, and their java level may then increase
  • Those actions are defined by Methods
slide12

Data:

  • Name: Elena
  • Java Level: 100
  • Actions:
  • Learn ( hours )
  • Data:
  • Name: Haydon
  • Java Level: 30000
  • Teaching Experience: 2000

Elena

Haydon

  • Data:
  • Name: Robert
  • Java Level: 120
  • Actions:
  • Learn ( hours )

Robert

class Student{

String name;

intjavaLevel;

public Student( String n, int l ){

name=n; javaLevel=l;

}

public void learn( int hours){

javaLevel = javaLevel + hours;

}

}

  • Data:
  • Name: Kevin
  • Java Level: 102
  • Actions:
  • Learn ( hours )

Kevin

The “learn” action

slide13

class Student{

String name;

intjavaLevel;

public Student( String n, int l ){

name=n; javaLevel=l;

}

public void learn( int hours){

javaLevel = javaLevel + hours;

}

}

  • Data:
  • Name: Elena
  • Java Level: 100
  • Actions:
  • Learn ( hours )

Elena

  • Data:
  • Name: Robert
  • Java Level: 120
  • Actions:
  • Learn ( hours )

Robert

  • Data:
  • Name: Kevin
  • Java Level: 102
  • Actions:
  • Learn ( hours )

What happened when a method is called?

After Robert having learnt Java for 1 hour, whose Java level will increase?

Kevin

Remember that when you learn Java, only your Java skill increases

When calling a method of an object, it does not affect other objects’ private data

simulate today s tutoring session
Simulate today’s tutoring session

class Student{

String name;

intjavaLevel;

public Student( String n, int l ){

name=n; javaLevel=l;

}

public void learn( int hours){

javaLevel = javaLevel + hours;

}

public void showStatus(){

System.out.println(name + " with Java level "

+ javaLevel);

}

}

class Tutor{

String name;

intjavaLevel;

intteachingExp;

public Tutor( String n, intl, intexp){

name=n; javaLevel=l; teachingExp=exp;

}

public void teach(Student s, int hours){

s.learn(hours);

}

}

Your code:

Tutor haydon = new Tutor( “Haydon”, 30000, 1000);

slide15

Please let me know your questions.

I will be here till 8:30pm