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The 10 th and 11 th tutoring session Fall, 2012 - PowerPoint PPT Presentation
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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
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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
- 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
- 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
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
- 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
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
- 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
- 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
- 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
- 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 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
- 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
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
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);
Please let me know your questions.
I will be here till 8:30pm
