Beginning Java

8/3/2019 Beginning Java

1/50

BeginningJava

iBooks Author


2/50

1In this chapter we will talk

about who developed java

and what is java?

Introduction To Java

iBooks Author


3/50

2

James GoslingThe picture you see on left is of JAMES GOSLING. He is theone who developed Java at Sun Microsystems in 1995.

His weblog - http://nighthacks.com /

Section 1

Inventor of Java?

iBooks Author
http://nighthacks.com/http://nighthacks.com/


4/50

3

Java

Java is a programming language which is used widely all over

the world. It is used for playing games online as well as for view-

ing 3d images. It is used for doing many other things on the

web.

It is one of the most powerful languages.

It is built completely on OOPs Principle. Every program in java

has to be written in classes.

Section 2

What is Java?

iBooks Author


5/50

2In this chapter we will learn

about the IDE that can be

used for coding in java.

IDE For Java

iBooks Author


6/50

5

Eclipse IDE

Eclipse IDE For Java Developers is one of the most famous pro-

grams used for developing in java.

It is available for Macintosh, Windows & Linux. This makes it

even more famous.

IIsM

Section 1

Eclipse IDE ForJava Developers

iBooks Author


7/50

6

Installing Eclipse IDE

Macintosh

1. Go to http://www.eclipse.org/downloads

2. Select Mac OS X (Cocoa) from drop-down

menu

3. Click on Mac OS X 32 Bit or Mac OS X 64 Bit

next to Eclipse IDE For Java Developers.

4. Select one of the servers or select bit-torrent

5. Download the .tar.gz file

6. Extract the file you downloaded

7. Drag the eclipse folder extracted to the Applica-

tions folder on your Mac OS X.

Windows

1. Go to http://www.eclipse.org/downloads

2. Select Windows from drop-down menu

3. Click on Windows 32 Bit or Windows 64 Bit next

to Eclipse IDE For Java Developers.

4. Select one of the servers or select bit-torrent

5. Download the .zip file

6. Extract the file you downloaded

7. Drag the eclipse folder extracted to the C:\Program

Files folder on your Windows XP/Vista/7

Linux (Ubuntu)

1. Go to Ubuntu Software Center

2. Search for Eclipse

3. Install Eclipse

MOVIE 2.1 Installing Java IDE

Learn how to install java ide on windows, macin-

tosh and linux.

iBooks Author
http://www.eclipse.org/downloadshttp://www.eclipse.org/downloadshttp://www.eclipse.org/downloadshttp://www.eclipse.org/downloads


8/50


about the basic oops

features in java. JUSTBASIC.........

Basic OOP Terms

iBooks Author


9/50

Features

1. Classes & Objects

2. Data Abstraction

3. Encapsulation

4. Inheritance

5. Polymorphism

6. Dynamic Binding

7. Message Passing

8

OOPsObject Oriented Programming is a way of coding whereby the

program is made up of different small parts for faster execution.

Programs are divided into classes which may have n number

of objects.

Why OOPs?

1. Data can be hidden from other functions

2. Functions can be created as and when required

3. Depends on use of objects and instances.

4. Make the program to get executed much faster.

5. All the features written on the left...........Blah blah blah

Section 1

Object OrientedProgramming

iBooks Author


10/50

9

What is A Object?

Objects are one the key terms in object oriented programming.

A object can be anything like dog, cat, television, desk, etc.

Every object has two things in common state and behavior

Lets consider a dog. A dog has state - name, color, breed and

behavior - fetching, barking, etc.

Lets consider another example of speaker. A speaker has

state - volume, frequency, etc and behavior - increase vol-

ume, decrease volume, change frequency

Section 2

Objects

iBooks Author


11/50

10

What is A Class?In real world there are thousands of automobile (like honda

civic, bentley, etc). There may be many automobile of same

make and model. At the end every automobile is made up of

the same components. So in object oriented terms an automo-

bile is taken as an instance or object of the class automobiles.

A class can have n number of instances or objects.

Syntax

class automobile {

----blah blah blah----

----blah blah blah----

}

* instance and object are one and the same thing

Section 3

Class

iBooks Author


12/50

11

Lets take another example:

1. Lets say there is a class of animals.

2. Now lets think about animal. Lion, Cheetah, Tiger, Cat, Dog, etc are all animals. But in object oriented terms they are considered as

an instance of the class animals.

3. Lion, Cheetah, etc will perform the tasks that we define in the class animals.

iBooks Author


13/50

12

Data AbstractionAbstraction in the process of selecting important data sets for

an Object in your software, and leaving out the insignificant

ones.

This same information can be used in different applications.

eg: lets say we are making a banking program.

we require info about the person who wants to open a account. this can

be his name, address, phone no, pan card no, rashion card, electricity

bill, etc...

but we just want some details of this like name, address, phone no. now

this same information can be used in maintaining employee database.

Section 4

Data Abstraction

iBooks Author


14/50

13

EncapsulationEncapsulation is the technique of making the fields in a class

private and providing access to the fields via public methods. If

a field is declared private, it cannot be accessed by anyone out-

side the class, thereby hiding the fields within the class. For this

reason, encapsulation is also referred to as data hiding.

Encapsulation can be described as a protective barrier that pre-

vents the code and data being randomly accessed by other

code defined outside the class. Access to the data and code is

tightly controlled by an interface.

The main benefit of encapsulation is the ability to modify our im-

plemented code without breaking the code of others who use

our code. With this feature Encapsulation gives maintainability,

flexibility and extensibility to our code.

Section 5

Encapsulation

iBooks Author


15/50

14

InheritanceInheritance can be defined as the process where one object of

one class acquires the properties of object/objects of another

class.

eg: lets consider a class vehicle which has some values of

speed, power, etc.

now we have another class truck. it has an object t1. so now t1

derives data of speed and power from class vehicle.

Section 6

Inheritance

iBooks Author


16/50

15

PolymorphismPolymorphism is the ability to take more than one form.

eg: consider you want to write a program on area. you want to find out

the area of circle, rectangle.

now rectangle requires length & breadth values while circle requires only

radius.

so we can have two functions for rectangle and circle with l,b as argu-

ments for rectangle and r as argument for circle.

so now when a user types only radius the area of circle is calculated

while if he types l & b it will give him area of rectangle.

this is also known as function overloading.

JUST READ THIS WE WILL DISCUSS IN DETAIL LATER.

Section 7

Polymorphism

iBooks Author


17/50

16

What is it?????Dynamic Binding basically means that a particular part of code

gets executed when it is called at run-time.

Section 8

Dynamic Binding

iBooks Author


18/50

17

Message Passing?Message Passing basically is a property of java via which ob-

jects can communicate with each other.

Section 9

Message Passing

iBooks Author


19/50


about the basic terms used

in a java program.

Basic Terms In AJava Program

iBooks Author


20/50

1. public

2. protected

3. private

this is a bit hard to understand in the beginning

since we have not talked about methods. so just

take it this way, public allows access to its contents

to various classes, private allows access to its

contents only in the class, protected allows access

to its contents in the class.

19

What is public

public classes, methods, and fields can be accessed from every-

where. The only constraint is that a file with Java source code

can only contain one public class whose name must also match

with the filename. If it exists, thispublic class represents the ap-

plication or the applet, in which case the public keyword is nec-

essary to enable your Web browser or appletviewer to show the

applet. You use public classes, methods, or fields only if you ex-

plicitly want to offer access to these entities and if this access

cannot do any harm. An example of a square determined by theposition of its upper-left corner and its size:

eg: public class Square { // public class

int x, y, size; // public instance variables

}

now the variables x, y, size are accessible by other classes.

public in public static void main basically means that the con-

tents of main function can be accessed by any other class inthe program.

Section 1

Access Specifiers

iBooks Author


21/50

20

protected

protected methods and fields can only be accessed within thesame class to which the methods and fields belong, within its sub-

classes, and within classes of the same package, but not from any-

where else. You use theprotected access level when it is appropri-

ate for a class's subclasses to have access to the method or field,

but not for unrelated classes.

private

private methods and fields can only be accessed within the sameclass to which the methods and fields belong. private methods and

fields are not visible within subclasses and are not inherited by

subclasses. So, theprivate access specifier is opposite to the pub-

lic access specifier. It is mostly used for encapsulation: data are

hidden within the class and accessor methods are provided. An ex-

ample, in which the position of the upper-left corner of a square

can be set or obtained by accessor methods, but individual coordi-

nates are not accessible to the user.

eg: public class Square { // public class

private double x, y // private (encapsulated) instance variables

public setCorner(int x, int y) { // setting values of private fields

this.x = x;

this.y = y;

}

public getCorner() { // setting values of private fields

return Point(x, y); } }

iBooks Author


22/50

21

default Access Specifier

If you do not set access to specific level, then such a class, method, or field will be accessible from inside the same package to whichthe class, method, or field belongs, but not from outside this package. This access-level is convenient if you are creating packages. For

example, a geometry package that contains Square and Tiling classes, may be easier and cleaner to implement if the coordinates of

the upper-left corner of a Square are directly available to the Tiling class but not outside the geometry package.

Overview of Access Specifier

Note the difference between the default access which is in fact more restricted than the protected access. Without access specifier (the

default choice), methods and variables are accessible only within the class that defines them and within classes that are part of the

same package. They are not visible to subclasses unless these are in the same package. protected methods and variables are visible

to subclasses regardless of which package they are in.

iBooks Author


23/50

5Lets write out first java

program.

Hello Java!

iBooks Author


24/50

23

Programclass test{

public static void main(String args[])

{

System.out.print(Hello Java);

}

}

Output

Hello Java

Section 1

Helloooo...Explanation --->

name of the class - test

main function header is - public static void main (String args[])

Keywords -

System.out.print >>> allows printing anything

public - the main function is public.

static - does not create an object and asks compiler to directly

execute the main function.

void - its a return type which does not return any value (we will

come to this later)

args[] - used for passing array of arguments (we will come to it

later.)

iBooks Author


25/50

6Lets Comment

Comments

iBooks Author


26/50

25

What is that!!!Now comments are something that may be anything that you

write. It is not taken as a part of code. It is usually used to ex-

plain what the program is about or it may be used to explain

some part of code.

3 Types

1. Single Line - Statements beginning with two forward slash.

eg: // hey this is a comment

2. Block Comments - Statements beginning with forward slash

and a star sign (/*) & ending with a star sign and a forward

slash (*/).

eg: /* hey this

is a

comment */

3. Documentation Comments - Statements beginning with for-

ward slash and two star sign (/**) & ending with a star signand a forward slash (*/).

eg: /**hey this is a comment */

Section 1

Comments

iBooks Author


27/50

7What variables and

datatypes? What is that?

Variables &Datatypes

iBooks Author


28/50

27

What is that????

Variables are assigned with some data. They are basically

given names. Names are easier to remember than values.

Lets try remembering our mathematic lectures where we use to

have word problems. There many times we were given values.

Lets say we have two values now 20 and 40. So basically we

use to assign two name to number 20 and 40 respectively.

eg: x = 20, y = 40

now in java x and y are the variable name.

now lets take another example. I have a string ie this is nayan

i store it in str = this is nayan

it means str is the variable.

Section 1

Variables

iBooks Author


29/50

28

What Are Datatypes?

Now we just talked about variables but java doesnt understandwhether we are specifying a number or string in the variable.

So in order to make java understand what that variable is ie

whether it is a integer, floating number or string we have da-

tatypes.

We will learn about different datatypes and how to use them

ahead.......

Section 2

Datatypes"

iBooks Author


30/50


31/50

30

We are going to talk only about primitive datatypes.

Data

TypeType Bit

Space

Req

Signed/

UnsignedRange

Default

Value

bytebyte-length

integer8 1 byte Signed -128 to 127 0

shortshort-length

integer16 2 bytes Signed -32768 to 32767 0

int integer 32 4 bytes Signed -2,147,483,648 to -2,147,483,647 0

long long integer 64 8 bytes Signed

-9,223,372,036,854,775,808 to

-9,223,372,036,854,775,807 0L

float

single

precision

decimal

32-bitIEEE754

4 bytes Signed

1.40129846432481707e-45 to

3.40282346638528860e+38 (positive

or negative)

0.0f

double

double

precision

decimal

64-bitIEEE754

8 bytes Signed

4.94065645841246544e-324d to

1.79769313486231570e+308d

(positive or negative)

0.0d

boolean True/False 1 bit FALSE

charsingle

character

16-bitUnicod

echaract

er

2 bytes Unsigned 0 to 65,535 \u0000

iBooks Author


32/50

31

WHY NO UNSIGNED DATA-TYPES IN JAVA???? (ASK GOSLING)

Read this answers of Dennis Ritchie (Developer C), Bjarne Stroustrup (Developer C++) and James Gosling (Developer Java).

Q. Programmers often talk about the advantages and disadvantages of programming in a "simple language." What does that

phrase mean to you, and is [C/C++/Java] a simple language in your view?

Ritchie: C (and the others for that matter) are simple in some ways, though they are also subtle; other, somewhat similar languages

like Pascal are arguably simpler. What has become clear is that aspects of the environment like libraries that aren't part of the core lan-

guage are much bigger and more complicated. The 1999 C standard grew hugely more in the library part than in the language; the

C++ STL and other things are big; AWT and other things associated with Java are too.

Stroustrup: I see three obvious notions of "simple:" to be easy to learn, to make it easy to express ideas, and to have a one-to-one

correspondence to some form of math. In those terms, none of the three languages is simple. However, once mastered, C and C++

make it easy to express quite complex and advanced ideas -- especially when those ideas have to be expressed under real-world re-

source constraints.

Gosling: For me as a language designer, which I don't really count myself as these days, what "simple" really ended up meaning was

could I expect J. Random Developer to hold the spec in his head. That definition says that, for instance, Java isn't -- and in fact a lot of

these languages end up with a lot of corner cases, things that nobody really understands. Quiz any C developer about unsigned, and

pretty soon you discover that almost no C developers actually understand what goes on with unsigned, what unsigned arithmetic is.

Things like that made C complex. The language part of Java is, I think, pretty simple. The libraries you have to look up.

Check the interview at - http://www.gotw.ca/publications/c_family_interview.htm

iBooks Author


33/50

32

Another Reason...You Could Say

I was digging through web pages and found this. Originally Java was known as Oak. One of its oldest guide says this

The specification says: "The four integer types of widths of 8, 16, 32 and 64 bits, and are signed unless prefixed by the unsigned modi-

fier.

In the sidebar it says: "unsigned isn't implemented yet; it might never be." How right you were.

Check Section 3.1 on http://www.artima.com/weblogs/viewpost.jsp?thread=7555

iBooks Author


34/50

33

Difference Between Unsigned & Signed?????

1. Unsigned datatypes can hold only positive values but their range increases

eg: if i have a datatype with range -127 to 128 then its unsigned will become 0 to 255

2. Signed datatypes can hold both positive and negative values.

String

String is nothing but a primitive datatype which helps in printing statements.

Default Value - null.

eg: This is Nayan, India is a country, Tech Barrack Solutions Pvt Ltd is a company

Default Value

Basically default value is either 0 or null. It is assigned to the datatype when the datatype is not initialized. And it works only for field

variables and not for local variables. The variables in the main function are local variables. We will learn about field variables later.

Syntax

datatype_namevariable_name = value;

eg: byte x = 10;

iBooks Author


35/50

8Lets learn how we can

import packages in java.

Java Packages

iBooks Author


36/50

35

What is it???Huh??

Just like in C++ where we have to include header files, in javawe import packages.

Benefits Of Packages In Java

The best part of java packages is we can import the class that

we require rather than importing the whole package.

Default Package

import java.lang.*;

Syntax

eg: importjava.package_name.class_name;

import java.util.Scanner;

importjava.package_name.*;

this imports all classes from that particular package

import java.io.*;

Section 1

Java Packages

iBooks Author


37/50

9Ahh..Escape....What!!!

Escape Sequences

iBooks Author


38/50

37

Section 1

Escape Sequences

Escape Sequence Function

\t inserts a tab

\b backspace

\n creates a new line

\r carriage return

\f form feed

\ inserts a single quote

\ inserts a double quote

\\ inserts a backslash

What is that?These are characters preceded by a backslash(\). They are

used in the System.out.print statements.

Syntax

System.out.print(\n hey);

iBooks Author


39/50

10What huh!!!!

Type Casting &Type Conversion

iBooks Author


40/50

39

Introduction

Now we have many data-types in java. But if we want to con-vert one data-type to another we make use of type conversion

or type casting.

Type Conversion

Now lets consider that we arrange data-types in ascending or-

der i.e. by that i basically mean from a data-type which holds

smaller value to one which holds the max value. So the data-

types in ascending order will be like this >>> byte, short, int,

long, float & double.

Type Conversion is kind of automatic conversion.

eg: So byte can be converted to short, int and long, float & dou-

ble only. ! short can be converted to int, long, float & double.

int can be converted to long, float & double.

long can be converted to float and double.

long can never undergo type conversion to int, short or byte.

int can never undergo type conversion into short or byte.

Similarly short can never undergo type conversion into byte.

Section 1

Type Conversion &

Type Casting

iBooks Author


41/50


42/50

41

Type Casting

We just learnt about Type Conversion now what is Type Cast-ing.

Okay so we saw that there are no automatic conversion from

large data-type to small data-type. Type Casting solves our

problem.

Syntax

data_typevariable_name = (data_type)either number or other variable;

eg:

class test{

public static void main(String args[]){

int x = 5;

short y = (short)x;

double z = (double)y;

long a = (long)z;

}

}

Explanation

int x get type casted to short y. And a integer type variable i.e.

short y gets converted to floating type i.e. double z. double z

gets converted to long z which is a integer type

iBooks Author


43/50

11Learn how to take input

from user in JAVA.

Taking Input FromUser

iBooks Author


44/50

Three Methods

1. Scanner

2. BufferedReader

3. Data InputStreamReader

43

Basically there are three methods by which input from a user

can be taken in java. We are only going to talk about the first

two methods.

Section 1

Input From User

iBooks Author


45/50

44

Scanner

Scanner is one the most common method used for taking inputfrom user in java.

We import the java.util package with class Scanner.


Syntax

Scanner sc = new Scanner (System.in);

int i = sc.nextInt();

Data - Type Syntax

byte sc.nextByte();

short sc.nextShort();

int sc.nextInt();

long sc.nextLong();

float sc.nextFloat();

double sc.nextDouble();

string sc.next(); or sc.nextLine();

boolean sc.nextBoolean();

Section 1.1

Scanner

iBooks Author


46/50

45

eg:


class test{


Scanner sc = new Scanner(System.in);

int i = sc.nextInt();

System.out.println(i);

}

}

Output >>

4

4

Explanationjava.util.Scanner -java.util is the package and Scanner is the

class inside the package.

Scanner sc - sc is the name of the scanner that we are going to

use in the program.

new Scanner - we are creating a object of sc using

new Scanner

System.in - it tells java to take input from keyboard.

int i = sc.nextInt() - takes integer input from user

System.out.println - prints the input taken from user.

iBooks Author


47/50

46

BufferedReader

This method of taking input from user is very commonly taughtto students in Educational Institutions.

In this method whatever input we take from user has to be

taken in the form of String. And then it has to be type casted

into a particular datatype. Basically type casted means con-

verted to desired data type.

We also have throw an exception in the main function for this

method.

SyntaxInputStreamReader isr = new InputStreamReader(System.in);

BufferedReader br = new BufferedReader(isr);

String str = br.readLine();

Section 1.2

BufferedReader"

Data - Type Syntax

byte Byte.parseByte();

short Short.parseShort();

int Integer.parseInt();

long Long.parseLong();

float Float.parseFloat();

double Double.parseDouble();

string br.readLine();

boolean Boolean.parseBoolean();

iBooks Author


48/50

47

eg:

import java.io.BufferedReader;

import java.io.InputStreamReader;

import java.io.IOException;

class test{


InputStreamReader isr = new InputStreamReader(System.in);

BufferedReader br = new BufferedReader(isr);

String str = br.readLine();

int i = Integer.parseInt();

System.out.println(i);

}

}

Output >>

4

4

Explanation

import java.io.* - we want 3 classes from the java.io package ieBufferedReader, InputStreamReader, IOException.

InputStreamReader isr - isr is the name of the InputStream-

Reader that we are going to use in the program.

new InputStreamReader - we are creating a object of isr using

new InputStreamReader

System.in - it tells java to take input from keyboard.

BufferedReader br - br is the name of BufferedReader that we

are going to use in the program

new BufferedReader - creates object of br

String str = br.readLine(); - takes input from the user in string for-

mat.

int i = Integer.parseInt(); - converts string input of user into inte-

ger.

System.out.println - prints the input taken from user.

instead we can also

write

import java.io.*;

iBooks Author


49/50

IDE

Integrated Development Environment. It is basically a platform used for programming

in a particular language.

Related Glossary Terms

Index

Drag related terms here

iBooks Author


50/50

Java

A programming language developed by james gosling at sun microsystems in 1995.

Related Glossary Terms

Index

Drag related terms here

iBooks Author

Beginning Java

Documents

Transcript of Beginning Java