Lec 2

BITS Pilani, Pilani Campus

BITS PilaniPilani Campus

Dr. Yashvardhan SharmaCSIS Dept., BITS-Pilani

IS F213 Object Oriented Programming


Today’s Agenda

• Compiling/Executing Java Programs (Review)• Object Basics• Three Pillars of OOP• Basic Java Syntax

• Java Type System

• Differences Between C & Java

• System.out.println() and System.out.print() methods


Java Features

• Compiled and Interpreted• Platform Independent• Architectural Neutral


Java Program Structure

Documentation Section1. /**…… */ Documentation Comments2. // Single Line Comment3. /*…… */ Multi line Comments

Package Statement

Import Statements

Interface Statements

Class Definitions

Main Method class


Compiling/Executing a Java Application

Source Code

Java Compiler

ByteCode

<< .java file>>

<< javac .java >>

<< .class file>>

Java Interpreter

Machine Code

<< java [name of class] >>


Example 1

class Test1{public static void main(String[] x){System.out.println("Hello Java");}} D:\programs>javac yash.java

D:\programs>java Test1Hello Java

D:\program>java test1Exception in thread "main" java.lang.NoClassDefFoundError: test1 (wrong name: Test1)

Name of Source File is

yash.java


Example 2

// oop.javaclass A{public static void main(String args[]){System.out.println("This is class A");}}class B{public static void main(String args[]){System.out.println("This is class B");}}

D:\programs>javac oop.java

D:\programs>java oopException in thread "main" java.lang.NoClassDefFoundError: oop

D:\programs>java AThis is class A

D:\programs>java BThis is class B


What’s Object

• Term Object Means Combination of Data (Attributes) and Logic (Behavior, Functions, Operations) of some real world entity

• Every object has two parts :- Data Part [ Instance Fields in Java, Attributes or properties]- Operations Part [ methods in java, Behavior]

• Examples :1. Account :

Attributes : Account Holder, Account type [saving , current] , Balance Operations : deposit, withdraw,

2. BOX: Attributes : length, width, height, color Operations : compute area, compute volume

Data

Methods Methods

Methods Methods

Object keeps Data Part + Operation Part Together


What’s class

• Objects are grouped in classes• Class collections of objects having similar

behavior and properties• A single object is simply an instance of class.• Objects can not be instantiated (or created)

without defining a class• Classes are defined whereas objects are

created.


Object State

• Properties/Attribute Values at a particular moment represents the state of an object

• Object may or may not change state in response to an outside stimuli. • Objects whose state can not be altered after creation are known as immutable

objects and class as immutable class [ String class in Java]• Objects whose state can be altered after creation are known as mutable objects

and class as mutable class [ StringBuffer class in Java]

States of Three Different INSTANCES of CAR CLASS

MARUTI800

Name : maruti800Price : 200789Color : Red

MarutiESTEEM

Name : marutiEsteemPrice : 500789Color : whilte

MARUTIZEN

Name : marutiZenPrice : 200789Color : metallic white


Data Abstraction

• Way of managing complexity• Abstraction refers to the act of representing

essential features that are of interest of the users without including background details or explanation

• Classes use the concept of encapsulation for hiding unnecessary implementation details


Pillars of OOP

• Encapsulation• Inheritance• Polymorphism


Encapsulation

• Encapsulation means wrapping up of data and methods (operations , code) together

• Access to code and data is tightly controlled. • Through we can define what and what can not be

accessible outside. [ public , private , protected ]

Data

Methods Methods

Methods Methods

Encapsulation keeps Data Part + Operation Part Together inside a capsule


Encapsulation Example

class BOX

{

private double length;

private double width;

private double height;

public double area() { }

public double volume() { }

} // End of class BOX

lengthwidthheight

area()

volume()

BOX Class


Inheritance

• Process by which one object acquires properties of other classes• Supports Reusability of code and data• The class whose properties are extended is known as super or base or

parent class.• The class which extends the properties of super class is known as sub

or derived or child class • In Java a class can either extends another class or can implement an

interface

A

B <<class>>

<<interface>>A

B

<<class>>

<<class>>

class B extends A class B implements A


Various Forms of Inheritance

A

B

Single Inheritance

A

B

Hierarchical Inheritance

X

A B C

X

A B C

MultiLevel Inheritance

A

B

C

A

B

C

A B

C

Multiple InheritanceNOT SUPPORTED BY JAVA

A B

C

SUPPORTED BY JAVA


Polymorphism

• Poly means many and morph means forms. • One Interface Many forms• One Interface for several general class of actions• In Java we have two types of polymorphisms

1. Compile-Time [ Method Overloading]2. Run-Time [ Method Overriding]


Method OverLoading

• Two methods are said to be overloaded if they have same name and different signatures.

• Signature of method means number of arguments to method and their types.

• Two methods are said to have different signatures if they differ in number of arguments they receive or their types

• Example Signature

1. int sum (int a, int b)

2. float sum (int a, float b)

3. double sum(double a , double b)

4. void draw();

sum(int,int)

sum(int,float)

sum(double,double)

draw()

Note : return type and name of arguments are not part of signatures

Signatures


Method Overloading Examples

1. void sum(int a,int b)

2. int sum(float a, float b)

3. double sum (double a , double b)

4. int sum(int a, float b)

5. float sum(float a,int b)

Overloaded Methods

1. void sum(int a,int b)

2. int sum(int x, int y)

3. double sum (double a , double b)

4. float sum(double a1, double b)

1,2 and 3,4 Not Overloaded

1,3 and 2,4 are overloaded


Java Type System

• Type specifies set values + set of operations that you can perform with those values

• Java is strongly Typed Language• Every Type in Java is one of the following: (i) Primitive Types( int, short, byte, long, char, float, double, boolean) (ii) A class Type (iii) An interface Type (iv) An array Type (v) null type [void is not type in java]


Java’s Primitive Types

Type Size Minimum Value Maximum Valuebyte 1 -128 +127

short 2 -32768 +32767

int 4 -2,147,483,648 +2,147,483,647

long 8 -9,223,372,036,854,775,808

+9,223,372,036,854,775,807

float 4 3.4e-038 3.4+038

double 8 1.7e-308 1.7e+308

char 2 0 65535

boolean 1 bit


C vs Java

• Does not have statements like goto, sizeof, typedef• Does not support data types as struct,union • No Explicit Pointer Type• No auto, extern, register, signed, unsigned • Java requires that function with no return type should be

explicitly declared as void void show() ; void print();• Java adds a new operator instanceof and >>> (unsigned

right shift)• Java adds a labelled break and continue statements• Return type of all conditional, logical or relational

expressions is boolean in java and not integer as in C.


Exampleclass test1{public static void main(String args[]){byte b = 24; byte b1 = 678;char x = 45;char y = 70000;char y1 = -25;short x1 = 238999;float f = 678.45;double f1 = 56.67;}}

D:\java\bin>javac test1.javatest1.java:6: possible loss of precisionfound : intrequired: bytebyte b1 = 678; ^test1.java:8: possible loss of precisionfound : intrequired: charchar y = 70000; ^test1.java:9: possible loss of precisionfound : intrequired: charchar y1 = -25; ^test1.java:10: possible loss of precisionfound : intrequired: shortshort x1 = 238999; ^test1.java:11: possible loss of precisionfound : doublerequired: floatfloat f = 678.45; ^5 errors


Example 2

int a=10;if(10)printf("Hello");elseprintf("Hi");}

OUTPUT

Hello

int a=10;if(10)S.O.P("Hello");elseS.O.P("Hi");}OUTPUTD:\java\bin>javac test100.javatest100.java:6: incompatible typesfound : intrequired: booleanif(a) ^1 error

In C In Java


Example 3% Operator

class test101{public static void main(String args[]){int a=100, b=90;System.out.println(a%b);double a1= 10.56, b1 =4.67;System.out.println(a1%b1);}}

D:\java\bin>java test101101.2200000000000006


Example 4 >>,<<,>>>

class test103{public static void main(String args[]){int x = -1024;System.out.println(x>>2);System.out.println(x<<2);System.out.println(x>>>2);}} D:\java\bin>java test103

-256-40961073741568


System.out.println()

• Prints/Displays output and shifts the print control to new line (Similar printf(“\n”) in C)

• Displays output only in String form• If parameter to it is not in String form then it

will be converted to string form by internally calling toString()

• + operator can be used to concatenate data from different types


Examples

• System.out.println(“Hello”+10);• System.out.println(10+20);• System.out.println(“10”+20);• System.out.println(“Hello: ”+20+”is my age”);

Note :+ opeartor is used for dual purpose addition,concatenation

Hello1030

1020

Hello20is my age


System.out.print()

• Prints/Displays output starting from the same line (Similar printf() in C)

• Displays output only in String form• If parameter to it is not in String form then it

will be converted to string form by internally calling toString()

• + operator can be used to concatenate data from different types


Examples

class test104{public static void main(String args[]){System.out.print("Hello");System.out.print("I am fine");System.out.println(" It is OK");}}

D:\java\bin>java test104HelloI am fine It is OK


Example 2

class test105{public static void main(String args[]){System.out.print("Hello");System.out.print("I am fine");System.out.println(" It is OK");System.out.println(" It is OK Again");}}

D:\java\bin>java test105HelloI am fine It is OK It is OK Again

Lec 2

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