Core Java Programming Language (JSE) : Chapter II - Object Oriented Programming.

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Java Programming
Language SE – 6
Module 2 : Object-Oriented
Programming

Objectives
● Define object modeling concepts: abstraction,encapsulation and
packages
● Discuss why you can reuse Java technology application code
● Define class, member, attribute, method, constructor, and package
● Use the access modifiers private and public as appropriate for the
guidelines of encapsulation
● Invoke a method on a particular object
● Use the Java technology application programming interface (API)
online documentation

Relevance
● What is your understanding of software analysis and design?
● What is your understanding of design and code reuse?
● What features does the Java programming language possess that
make it an object-oriented language?
● Define the term object-oriented.

The Analysis and
Design Phase
● Analysis describes what the system needs to do:
Modeling the real-world, including actors and activities, objects,
and behaviors
● Design describes how the system does it:
– Modeling the relationships and interactions between objects and
actors in the system
– Finding useful abstractions to help simplify the problem or
solution

Abstraction
● Functions – Write an algorithm once to be used in many situations
● Objects – Group a related set of attributes and behaviors into a class
● Frameworks and APIs – Large groups of objects that support a
complex activity; Frameworks can be used as is or be modified to
extend the basic behavior

Classes as Blueprints for
Objects
● In manufacturing, a blueprint describes a device from which many
physical devices are constructed.
● In software, a class is a description of an object:
– A class describes the data that each object includes.
– A class describes the behaviors that each object
exhibits.

Classes as Blueprints for
Objects
● In Java technology, classes support three key features of object-
oriented programming (OOP):
– Encapsulation
– Inheritance
– Polymorphism

Declaring Java Technology
Classes
● Basic syntax of a Java class:
<modifier>* class <class_name> {
<attribute_declaration>*
<constructor_declaration>*
<method_declaration>*
}

Declaring Java Technology
Classes
public class Vehicle {
private double maxLoad;
public void setMaxLoad(double value) {
maxLoad = value;
}
}

Declaring Attributes
●
Basic syntax of an attribute:
<modifier>* <type> <name> [ = <initial_value>];
●
Examples:
public class Foo {
private int x;
private float y = 10000.0F;
private String name = "Bates Motel";
}

Declaring Methods
Basic syntax of a method:
<modifier>* <return_type> <name> ( <argument>* ) {
<statement>*
}

Declaring Methods
public class car{
private int modelno;
private String colour;
public void dispInfo(int mno,String col) {
modelno=mno;
colour=col;
}
}

Declaring Methods
Example-2
public class Dog {
private int weight;
public int getWeight() {
return weight;
}
public void setWeight(int newWeight) {
if ( newWeight > 0 ) {
weight = newWeight;
}
}

Accessing Object Members
● The dot notation is: <object>.<member>
● This is used to access object members, including attributes and
methods.
● Examples of dot notation are:
● a.dispInfo(101,”green”);
● a.modelno=”101”;

Example
// create a class car that will display the model number and
colour of car.
class car
{
int modelno;
String colour;
void dispInfo(int mno,String col)
{
modelno = mno;
colour = col;
}
}

Example -2
class carTest
{
car c1=new car();
c1.dispInfo(101,”green”);
}
}

Encapsulation
● Hides the implementation details of a class
● Forces the user to use an interface to access data
● Makes the code more maintainable
CarCar
colour String
model_no int
disp_info() void
Move() void

Declaring Constructors
●
Basic syntax of a constructor:
[<modifier>] <class_name> ( <argument>* ) {
<statement>*
}
●
Example:
public class Car {
private int speed;
public Car() {
speed = 50;
}
}

The Default Constructor
● There is always at least one constructor in every class.
● If the writer does not supply any constructors, the default
constructor is present automatically:
– The default constructor takes no arguments
– The default constructor body is empty
● The default enables you to create object instances with new
Xxx()without having to write a constructor.

Source File Layout
● Basic syntax of a Java source file is:
[<package_declaration>]
<import_declaration>*
<class_declaration>+

Source File Layout
package shipping.reports;
import shipping.domain.*;
import java.util.List;
import java.io.*;
public class VehicleCapacityReport {
private List vehicles;
public void generateReport(Writer output) {...}
}

Software Packages
● Packages help manage large software systems.
● Packages can contain classes and sub-packages.

The package Statement
●
Basic syntax of the package statement is: package
– <top_pkg_name>[.<sub_pkg_name>]*;
●
Examples of the statement are:
– package shipping.gui.reportscreens;
●
Specify the package declaration at the beginning of the source file.
●
Only one package declaration per source file.
●
If no package is declared, then the class is placed into the default
package.
●
Package names must be hierarchical and separated by dots.

The import Statement
● Basic syntax of the import statement is:
Import<pkg_name>[.<sub_pkg_name>]*.<class_name>;
OR
import<pkg_name>[.<sub_pkg_name>]*.*;
● Examples of the statement are:
import java.util.List;
import java.io.*;
import shipping.gui.reportscreens.*;

The import Statement
The import statement does the following:
● Precedes all class declarations
● Tells the compiler where to find classes

Compiling Using the -d
Option
cd JavaProjects/ShippingPrj/src
javac -d ../classes shipping/domain/*.java

Recap
● Class – The source-code blueprint for a run-time object
● Object – An instance of a class;
also known as instance
● Attribute – A data element of an object;
also known as data member, instance variable, and data field
● Method – A behavioral element of an object;
also known as algorithm, function, and procedure

Recap
● Constructor – A method-like construct used to initialize a new object
● Package – A grouping of classes and sub-packages

Java Technology API
Documentation
● A set of Hypertext Markup Language (HTML) files provides
information about the API.
● A frame describes a package and contains hyperlinks to information
describing each class in that package.
● A class document includes the class hierarchy, a description of the
class, a list of member variables, a list of constructors, and so on.

Java Technology API
Documentation

Core Java Programming Language (JSE) : Chapter II - Object Oriented Programming.

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