Download - Unit 1 Intro to Object Oriented Programming PT1

7/29/2019 Unit 1 Intro to Object Oriented Programming PT1

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Unit 1: Introduction to Object OrientedProgramming

public class Car{private String name;private String model;private String color;private int year;

}


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Objectives

At the end of this unit students should be able to:

PT1

1. Outline the basic ideas behind object oriented programming

2. State what is a class and how a class is related to an object

3. Demonstrate the creation(definition) of a simple class structure (with variables and

methods)

4. Define and use instance variables, class variables, instance methods and class

methods

5. Define constructors for classes.

6. Create objects of a class

PT2

7. Describe method and constructor overloading and construct classes that have

overloaded methods and constructors

8. Use the Java Class Library and existing classes

9. Define, create and use java packages

10. Differentiate between the various access modifiers and when it is appropriate touse them


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Object Oriented Program?

An Object-Oriented Program consists of a group ofcooperating objects, exchanging messages, for the

purpose of achieving a common objective.


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Objective:2

State what is a class and how a class related to anobject


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Object

An objectis a self-contained entity.

It has its own private collection ofattributes/fields

(ie. data or properties) and operations/methods (ie.

behaviour ) thatencapsulate functionality into a

reusable and dynamically loaded structure.


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Classes

The basic element of object-oriented programmingis a class.

A class is a software blueprint that can be used to

instantiate or create many individual objects.

A class: defines attributes /state which are variables which can

store a value that represents a particular property defines the methods that manipulate the object or perform

interaction between related objects and methods


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Objective: #3

Demonstrate the creation(definition) of a simpleclass structure (with variables and methods)


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UML Notation for Classes

Example

Class Name

Attribute

Methods


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Classes contd.

A Class defines a new Reference Data Type

A class defines the shape and behaviour of an

object and is a template for multiple objects with

similar features.

Once defined this new data type can be used to

create objects of that type

Thus, a class is a template for an object, and an

object is an instance of a class.

Example : Car audi = new Car();


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Class contd.

When you declare a class, you declare its exact formand nature. You do this by specifying the data that it

contains(fields/attributes) and the code that

operates on that data(methods).

While very simple classes may contain only code or

only data, most real world classes contains both


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Syntax is: class {

//***

}

Classes contd.

The requirements for thecreation of a class include a

source file with the ,

class keyword, followed by a

legal identifier

and a pair of curly braces for

the body.


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Code:

public class Car{//private String model;private String make;private int year;

private String color;

public Car(){}

public void setMake(){}

public String getMake(){}

}

Classes contd.


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Objective:#4

Define and use instance variables, class variables,instance methods and class methods


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ATTRIBUTES & METHODS

The attributes (state, data or variables) definedwithin the class are sometimes referred to as

instance variables.

The code for the behaviour of the objects of the

class are contained within the method

Collectively the methods and variables within theclass are called members of the class.


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Declaring Attributes

The elements of attribute declaration are:

Syntax is:

Example

public int name;


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For example, if the Books name, the authors

name, number of pages of a Book class are itsattributes. So the definition of the Book class wouldbe:

public class Book{

private String name;private String authorname;private int nopages;

}


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Methods

Class behaviour are represented in Java by methods

Java methods are similar to functions or procedures

in other programming languages

Methods are a series of statements that perform

some repeated task. Instead of writing 10 lines of

code we can put those ten lines in a method and

just call it in one line.


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Methods

Modules in Java are called methods and classes.

Java program are written by combining new

methods and classes the programmers write with

prepackaged methods and classes available in the

Java API

Classes generally consists of two things:

Instance variables (Attributes)

Methods Methods allow the programmmer to modularize

program


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Declaring Methods

The elements of method declaration are: :

:

:

:

Syntax is:

(){//body of code

}


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Methods

return_typespecifies the type of data returned

by the method. (this can be any valid type

including class types that you create) If the

method does not return a value, the type mustbe set to void

public String getName(){

return name;

}

public void setName(String name){

this.name=name;

}


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Methods that have a return type other than

void, return a value to the calling routine using

the following return statements:

Here value is the value returned.

Syntax is:return value;


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method_namespecifies the name given to themethod.(this can be any legal identifier other than

those already used by other items within the

current scope).

public String getName(){

return name;

}


this.name=name;

}


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Parameters-this is a sequence of type and identifierpairs separated by commas.

Parameters are essential variables that receive the

value of arguments passed to the method when it is

called.

If the method has no parameters, then the parameter

list will be empty.public String getName(){

return name;}


this.name=name;

}


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local variables All variable declared in method definitions

they are known only in the method in which they are

defined.

A methods parameters are also local variables


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Lets look at the example

Book.java

Book

- name: String

- author: String

- nopages: int

+ Book ()

+ getName(): String

+ getAuthor(): String+ getNoPages():int

+ setName(String):void

+ setAuthor(String):void

+setNoPages(int):void


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Objective:#5

Define constructors for classes.


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Constructor

A constructor initializes anobject immediately uponcreation.

It has the same name as the

class in which it resides andis syntactically similar to amethod.

Once defined, it isautomatically calledimmediately after the objectis created, before the newoperator completes.

Book

- name: String

- author: String

- nopages: int

+ Book ()

+ getName(): String

+ getAuthor(): String

+ getNoPages():int

+ setName(String):void

+ setAuthor(String):void

+setNoPages(int):void


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Constructor

Constructors do not have a return type, not evenvoid

It is the job of the constructor to initialize the

internal state of an object, so that the code creating

an instance will have fully initialized usable objectsimmediately

Constructors like methods can receive parameters//Constructor1

public Book(){name = "Java Programming";

authorname=" ";

nopages = 0;

}

//Constructor2

public Book(String n, String an, String n, int p){name= n;

authorname=an;

nopages = p ;

}


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Constructors need not be explicitly called becauseconstructors are called during the object creation and

should be provided with the required parameters if any.

Book java=new book(Patrick Norton);

The above object creation(java) gives a call to theconstructor which takes string parameter.

Whenever such definition of the constructor or list of

constructor are made it is said that the constructors are

overloaded. Will be discussed in details later

Such cases one constructor among the list of constructors is

called depending upon the object creation


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Lets look at the example Book.java

BookApp.java


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Objective:6#

Create objects of a class


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Declaring Objects

When you create a class you are creating a newdata type.

You can use this type to declare objects of that type.


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Declaring Objects

Obtaining objects is a two step process.

1. Declare the variable of the class type (does not

define and object

2. Acquire a physical copy of the object and assign itto that variable. (this is done using the new

operator.

Example:Book b = new Book();


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The New Operator

The new operator allocates memory for an object and

returns a reference to that object. The reference is thenstored in the variable.

b is the reference to an instance of Book.

Java automatically reclaims the memory used by the objectwhen it is no longer referred to by any variable.

When a new object is created a distinct set of instance

variables are obtained. The instances of the class are created during the program

execution and discarded as and when required.

Example:Book b= new Book();


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Difference between Class and Object

A class creates a new data type that can be use tocreate objects

A class creates a logical framework that defines the

relationship between members

A class is like a blueprint from which an object is

built.


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Difference between Class and Object

When you declare an object of a class, you aredeclaring an instance of that class

Hence,

a class is a logical construct.

an objecthas physical reality


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Dot Operator

The dot notation is used to obtain the value of the

instance variables.

. Where objectReference is the name of the object

and variable name is the instance variable.


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Invoking a Method

A method is invoked (i.e. made to perform itsdesignated task)by a method call.

The method call specifies the method name and

provides information (as arguments) that the called

methods needs to do its tasks


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Method Call

Calling a method is similar to calling or referring toan instance variable.

The methods are accessed using dot operator alongwith the object.

Syntax is:Objectname.Methodname(param1,param2,);

Example:Book b = new Book();

b.setName(The World Prose);


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Lets look at the example BookApp.java


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Additional Reading

http://java.sun.com/docs/books/tutorial/java/package/namingpkgs.html

http://www.jarticles.com/package/package_eng.html

http://www.entertainingcode.com/archives/design-fundamentals-

encapsulation/
http://java.sun.com/docs/books/tutorial/java/package/namingpkgs.htmlhttp://java.sun.com/docs/books/tutorial/java/package/namingpkgs.htmlhttp://www.jarticles.com/package/package_eng.htmlhttp://www.jarticles.com/package/package_eng.htmlhttp://java.sun.com/docs/books/tutorial/java/package/namingpkgs.htmlhttp://java.sun.com/docs/books/tutorial/java/package/namingpkgs.html

Download - Unit 1 Intro to Object Oriented Programming PT1

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