Object-Oriented Programming with Java Oum Saokosal , Head of IT Department National Polytechnic Institute of Cambodia Tel: (855)-12-417214 E-mail: oum_saokosal@yahoo.com

Chapter 6 Objects and Classes (Revision) OOP Classes Objects Constructors Accessing Object’s Data and Methods

OOP

Classes

Objects

Constructors

Accessing Object’s Data and Methods

Object-Oriented Programming Why learning OOP? Java is a pure OOP OOP provides more flexibility, modularity, clarity, reusability Other Programming: C++, C#, VB .NET, ActionScript 3.0, Ruby etc. also use OOP. 3 concepts of OOP: Class Encapsulation Class Inheritance Polymorphism

Why learning OOP?

Java is a pure OOP

OOP provides more flexibility, modularity, clarity, reusability

Other Programming: C++, C#, VB .NET, ActionScript 3.0, Ruby etc. also use OOP.

3 concepts of OOP:

Class Encapsulation

Class Inheritance

Polymorphism

Classes (1) What is a class? A class is similar to a template, blueprint or symbol (in Adobe Flash). A class creates many objects. Class Objects

What is a class?

A class is similar to a template, blueprint or symbol (in Adobe Flash).

A class creates many objects.

Classes (2) In a class, there are : Data Fields (Properties) Behavior: Constructors Methods public class Student { private int id, String name; public Student(){} public Student (int inputID, String inputName){ this.id = inputID; this.name = inputName; } public String toString(){ return id + name; } }

In a class, there are :

Data Fields (Properties)

Behavior:

Constructors

Methods

Constructors (1) What is constructor? A constructor is to construct (create) objects from a class. public class Student { private int id, String name; public Student(){} public Student (int inputID,String inputName){ this.id = inputID; this.name = inputName; } public String toString(){ return id + name; } }

What is constructor?

A constructor is to construct (create) objects from a class.

public class Student {

private int id, String name;

public Student(){}

public Student (int inputID,String inputName){

this.id = inputID;

this.name = inputName;

}

public String toString(){

return id + name;

}

}

Constructors (2) How to construct objects? Usually, we have many classes in a projects. So the student class will be created in other classes. To construct objects from student class: public class TestStudent { public static void main(String[] args){ Student stu; //To construct an object stu = new Student(); System.out.println(stu.toString()); } }

How to construct objects?

Usually, we have many classes in a projects. So the student class will be created in other classes.

To construct objects from student class:

public class TestStudent {

public static void main(String[] args){

Student stu;

//To construct an object

stu = new Student();

System.out.println(stu.toString());

}

}

Access Object’s Data and Methods To access method: public class TestStudent { public static void main(String[] args){ Student stu; //To construct an object stu = new Student(“123”,”Veasna”); System.out.println( stu.toString() ); } } To access data: Usually, We don’t access the data. If you like, you can do like : stu.id = 123 in case id is not private .

To access method:

public class TestStudent {

public static void main(String[] args){

Student stu;

//To construct an object

stu = new Student(“123”,”Veasna”);

System.out.println( stu.toString() );

}

}

To access data:

Usually, We don’t access the data. If you like, you can do like : stu.id = 123 in case id is not private .

End of Revision