Java Basic concepts

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JAVA BASICS
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Java is a Programming Language
Java is a programing language.
just like any other primitive language such
as C, C++, Pascal.
It has
o Variables
o Functions
o Data Type
o Control Statement
o Arrays

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Java is OOP
3 Idiot
Java is Object Oriented Programming .
follows OOP methodology.
Java thinks only Objects.
Meri
4 Lakh
ki watch
Just like a Money Oriented Person
who always thinks of Money.

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Basic Unit of Java is Object
Such as program of
o sum of two numbers is an object
o Fibonacci Series is an object
o SMS Services is an object
o Email Services is an object
o Account Services is an object
Basic unit of Java is an Object.

5. Expert Object
Each Object is an Expert object.
Expert object contains related variables and
functions.
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6. An Expert never overlaps responsibilities
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Creator
Preserver
Destroyer
Trimurti

7. Experts bring Modularity and Reusability
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Object has State & Behavior
Object has state and behavior.
State will be changed by behavior.

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Object has State & Behavior
States are stored in memory variables.
Behavior changes states.
Behaviors are implemented by functions;
functions are referred as methods in OOP
Variables and Methods of an object are
defined by Class.
Class is the structure or skeleton of an
Object.

10. Class vs Objects
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Realization
Realization
State/Variables
currentGear
Speed
Color
Methods
changeGear()
Accelerator()
break()
changeColor()
State/Variables
name
address
Methods
changeName()
changeAddress()
Design
Real world entities based
on design

11. Class is the basic building block
 The basic building block of Java is a Class.
 Java program is nothing but a Class.
 Java application is made of Classes.
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Class
Class contains methods and variables.
Variables contain values of type int,
float, boolean, char and String.
Methods perform operations.

13. Executable Class
An executable Class must have default
method ‘main’ .
Method main() is the entry point of a class.
main() is called by JVM at runtime.
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Program
Program Structure - Primitive Language
int i = 5 //global variable
void main(){
..
a(5);
}
void a(int k){
int j = 0; //local variable
..
}

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Primitive Language Library
Library
Program 1 Program 2
Program 3 Program 4
 Library is made of multiple reusable programs.

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Class
Program Structure - Java
int i = 5 //global variable
void main(){
..
a(5);
}
void a(int k){
int j = 0; //local variable
..
}

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Java Library - API
Package
Class 1 Class 2
Class 3 Class 4
 Package is made of related classes.

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JAVA Application
ApplicationApplication
Package 1 Package 2
Package 3 Package 4
 Application is made of multiple packages

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Java Program is a Class
public class HelloJava {
…
}
A class may contain multiple variables and
methods.
A Class should have default ‘main’ method that is
called by JVM at the time of execution.

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My First Program - HelloJava
public class HelloJava {
opublic static void main(String[] args) {
o String name =“Vijay”;
o System.out.println("Hello “ + name);
o}
}
public, class, static, and void are keywords.
Keywords are always written in small letters.

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Keywords
class – is used to define a class.
public – Access modifier shows accessibility of a
class or variable or method to other Java classes.
There are 3 access modifiers public, protected and
private.
static – Memory for the static variables is
assigned only once in life. Non-static variables are
called instance variables.
void – is a NULL return type of main method.

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Statements
System.out.println() method is used to write text at
standard output device – Console.
String is a data type.
Two strings are concatenated by + operator
o String name = “Vijay” ;
o “Hello” + name is equal to “Hello Vijay”.

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JAVA_HOME
 Java is installed at “C:Program FilesJavajdkx.x.”
 It is known as JAVA_HOME
 JAVA_HOMEbin folder contains
o javac.exe – Java Compiler
o java.exe – JVM ( Java Virtual Machine)

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Compile Program
Open command prompt
Create c:sunrays
Change directory to c:sunrays
Compile program by
o javac HelloJava.java
o It will create HelloJava.class
Execute class file by
o java HelloJava

25. Java Platform
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JDK
JRE
Development Kit
javac.exe
JVM
(java.exe)
JAVA Class Libraries
AWT, I/O, Net etc.

26. Compile and Execute
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Hello.java
(text)
JVM (java.exe)
Hello.class
(bytecode)
Compile (javac)
• Compile .java file
• c:testjavac Hello.java
• It will generate file Hello.class
• Run the class by
• c:testjava Hello

27. Compile once run anywhere
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JVM
Linux
Hello.class
(bytecode)
JVM
MacOS
JVM
Windows

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Control Statement
if-else
while
for
do-while
GOTO
28

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While Loop
29

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While Loop
 public class HelloWhile {
 public static void main(String[] args) {
o boolean जबतकहेजान = true;
o int round = 0;
o while (जबतकहेजान ) {
 System.out.println(“मै बसंती नाचूंगी !!!");
 round++;
 if(round>500 )
• जबतकहेजान = false;
 }
 }
 }
30

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For Loop 10$ for 5 shots
How Much?
Okay!!
31

32.  public class HelloFor {
 public static void main(String[] args)
 {
o for (int shot=1; shot <= 5; shot++)
o {
 System.out.println(i+“Shot Balloon");
o }
o }
 }
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For Loop – Five shots
32

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Print Hello Java 5 times - for
public class HelloFor {
public static void main(String[] args) {
o for (int i = 0; i < 5; i++) {
 System.out.println("Hello Java ");
o }
o }
}

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Print Hello Java 5 times - while
public class HelloWhile {
public static void main(String[] args) {
o int i = 0;
o while (i < 5) {
 System.out.println("Hello Java ");
 i++; // i = i+1
o }
}
}

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Print Hello Java 5 times – do-while
public class HelloDoWhile {
public static void main(String[] args) {
int i = 0;
o do {
 System.out.println( i+ " Hello Java ");
 i++;
o } while (i < 5);
}
}

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Foreach statement
public class HelloFor {
public static void main(String[] args) {
o int[] table={ 2, 4, 6, 8, 10};
o for (int v : table) {
 System.out.println(“Table “ + v);
o }
o }
}

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Add.java
public class Add {
public static void main(String[] args) {
oint a = 5;
oint b = 10;
oint sum = a + b;
oSystem.out.println("Sum is " + sum);
}
}

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Java Primitive Data Types
Primitive Data Types:
o boolean true or false
o char unicode (16 bits)
o byte signed 8 bit integer
o short signed 16 bit integer
o int signed 32 bit integer
o long signed 64 bit integer
o float,double IEEE 754 floating point

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java.lang.String class
 String name = "Vijay Dinanath Chauhan";
 S.o.p(" String Length- " + name.length());
 S.o.p(" 7th character is- " + name.charAt(6));
 S.o.p(" Dina index is- " + name.indexOf("Dina"));
 S.o.p(" First i Position- " + name.indexOf("i"));
 S.o.p(" Last i Position- " + name.lastIndexOf("i"));
 S.o.p(" a is replaced by b- " + name.replace("a", "b"));
 S.o.p(" All a is replaced by b- “ + name.replaceAll("a", "b"));
 S.o.p(“ Chhota vijay- " + name.toLowerCase());
 S.o.p(" Bada vijay- " + name.toUpperCase());
 S.o.p(" Starts With Vijay- " + name.startsWith("Vijay"));
 S.o.p(" Ends with han- " + name.endsWith("han"));
 S.o.p(" Substring- " + name.substring(6));
 Note : S.o.p = System.out.println

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Java.lang.StringBuffer class
 public static void main(String[] args) {
 StringBuffer sb = new StringBuffer("Vijay");
 sb.append(“ Dinanath Chauhan");
 S.o.p("Length : " + sb.length());
 S.o.p("Capacity :" + sb.capacity());
 S.o.p("Char at :" + sb.charAt(1));
 S.o.p("Index Of : " + sb.indexOf("Dinanth"));
 S.o.p("Replace : " + sb.replace(0, 5, "Jay "));
 S.o.p("Reverse : " + sb.reverse());

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String vs StringBuffer
String is immutable
o Memory object can not be changed.
StringBuffer is mutable
o Memory object can be changed.

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java.lang.Math class
 public static void main(String[] args) {
o S.o.p(“ Mathematics functions");
o S.o.p(" Max 2,5 - " + Math.max(2,5));
o S.o.p(" Min 2,5 - " + Math.min(2,5));
o S.o.p(" Absolute 3.7 - " + Math.abs(3.7));
o S.o.p(" Exp 10 - " + Math.exp(10));
o S.o.p(" Random Number- " + Math.random());
o S.o.p(" Square Root- " + Math.sqrt(4));
 }
 Note : S.o.p = System.out.println

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Static vs Instance
String name = “Vijay”;
String surname = “Chauhan”
S.o.p(name.length());
S.o.p(surname.length());
String.length()
S.o.p(Math.max(2,5));
S.o.p(Math.max(5,10));

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Other Data Types
Reference types (composite)
o objects
o arrays
strings are supported by a built-in class
named String (java.lang.String).
string literals are supported by JAVA as a
special case.

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Hello <Name>
 public class HelloName {
o public static void main(String[] args) {
o System.out.println("Hello " + args[0]);
o }
 }
 C:>java HelloName Vijay Dinanath Chauhan
 class args[0] args[1] args[2]
 C:>java HelloName “Vijay Dinanath” Chauhan

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Hello Name – if <condition>
 public class HelloName1 {
 public static void main(String[] args) {
o if (args.length == 1) {
 System.out.println("Hello " + args[0]);
o } else {
 System.out.println(“Parameter name is required");
o }
 }
 }

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Hello All
public class HelloAll {
public static void main(String[] args) {
o for (int i = 0; i < args.length; i++) {
 System.out.println(i + " = Hello " + args[i]);
o }
}
}

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Hello All (Cond)
public static void main(String[] args) {
int size = args.length;
if (size == 0) {
o S.o.p("Usage : java HelloAll n1 n2 n3 .. ");
} else {
o for (int i = 0; i < size; i++) {
o S.o.p ( i+ " = Hello " + args[i]);
o }
}
}

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Hello All - switch
public static void main(String[] args) {
int size = args.length;
switch(size) {
case 0 :S.o.p("Usage : java HelloAll1 n1 n2 n3..");
o break;
case 1 : S.o.p(“Hello “ + args[0]); break;
default :
o for (int i = 0; i < size; i++) {
 S.o.p(i + " = Hello " + args[i]);
o }//for
}//switch
}//method

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Add.java – Integer Arguments
public class Add {
public static void main(String[] args) {
oint a = Integer.parseInt(args[0]);
oint b = Integer.parseInt(args[1]);
oint sum = a + b;
oSystem.out.println("Sum is " + sum);
}
}
C:>java Add 10 20

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Division
 public class Division {
o public static void main(String[] args) {
o int a = Integer.parseInt(args[0]);
o int b = Integer.parseInt(args[1]);
o double div = a/b;
o System.out.println("Division is " + div);
o }
 }

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Define a Method
 public static void main(String[] args) {
o printAll(args);
 }// main
 public static void printAll(String[] args) {
o for (int i = 0; i < args.length; i++) {
 System.out.println(“Hello " + args[i]);
o }
 }//printAll

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Return a Value
 public static double getDivision(int a, int b)
o {
 double div = a / b;
 return div;
o }
 }

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Command line Menu
 public static void main(String[] args) throws Exception{
 int ch = System.in.read(); //Read data from keyboard
 System.out.println( "Selected char ASCII Code " + ch);
 if (ch == 'A' || ch == 'a') {
 Add.main(args);
o } else if (ch == 'D' || ch == 'd') {
 Division.main(args);
o } else {
 S.o.p("Incorrect Choice ");
o }
o }
 }

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10
One Dimension Array
20
[0]
18
..
10
8
6
4
2
[1]
[8]
[9]
[2]
[3]
[4]
[n]
length
int[] table = new int[10];
int a = table[4];
int a = table[2];
int size = table.length;

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10
Initialize an Array
20
[0]
18
..
10
8
6
4
2
[1]
[8]
[9]
[2]
[3]
[4]
[n]
length
int[] table = new int[10];
table[0] =2;
table[1] =4;
….
Or
int[] table =
{2,4,6,8,10,12,14,16,18,20};

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Other Data Type Arrays
char[] chList = new char[5];
chList[0] = ‘A’….
o Or
char[] chList = {‘A’,’B’,’C’,’D’,’E’}
String[] strList = new String[5];
strList[0] = “A”
strList[1] = “Bee”
o Or
String[] strList = {“A”,”Bee”,”Cee”,”Dee”,”E”}

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Copy an Array
public static void main(String[] args) {
o char[] copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e', 'i', 'n',
'a', 't', 'e', 'd' };
o char[] copyTo = new char[7];
o System.arraycopy(copyFrom, 2,
o copyTo, 0, 7);
o S.o.p(new String(copyTo));
}
Start
Index
Start
Index
No Of
Element

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One Dimension Array
int[] table;
table = new int[10];
table[0] =2;
table[1] =4;
4B
10
[0]
[1]
[9]
length
2
4
20
1000
1000
table

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10length
2D Array
[0]
20
18
..
10
8
6
4
2
[1]
[8]
[9]
[2]
[3]
[4]
[n]
30
27
..
15
12
9
6
3
40
36
..
20
16
12
8
4
90
81
..
45
36
27
18
9
100
90
..
50
40
30
20
10
…
[0] [1] [2] [7] [8]
9
9
..
9
9
9
9
9

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int[][] table = new int[10][9];
table
1010
1000
1000
1011
1111
1010
1011
1111

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Define an Array
 int[][] table = new int[10][9];
 table[1][5] = 5;
 int size = table.length;
 int size = table[0].length;
 int[][] rows = new int[10][];
 rows[0] = new int[9];
 rows[1] = new int[19];
 rows[2] = new int[29];
 int[][][] xyz = new int[10][9][2];

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3D Array
20
[0]
18
..
10
8
6
4
2
[1]
[8]
[9]
[2]
[3]
[4]
[n]
30
27
..
15
12
9
6
3
40
36
..
20
16
12
8
4
90
81
..
45
36
27
18
9
100
90
..
50
40
30
20
10
[0] [1] [2] [8] [9]
20
18
..
10
8
6
4
2
30
27
..
15
12
9
6
3
40
36
..
20
16
12
8
4
20
18
..
10
8
6
4
30
27
..
15
12
9
6
20
18
..
10
8
6
4
2
30
27
..
15
12
9
6
3
40
36
..
20
16
12
8
4
90
81
..
45
36
27
18
9
100
90
..
50
40
30
20
10
90
81
..
45
36
27
18
9
100
90
..
50
40
30
20
10
…
[0]
[1]
[2]

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java.util.Date class
 import java.util.*;
 public class TestDate {
 public static void main(String[] args) {
o Date d = new Date();
o S.o.p("Date : " +d);
o S.o.p ("Long Time : " +d.getTime());
 }
 Output
o Date : Mon Jan 04 00:35:53 IST 2010
o Long Time : 1262545553156

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Format a Date
 import java.util.*; import java.text.SimpleDateFormat;
 public class TestDateFormat{
 public static void main(String[] args) {
o Date d = new Date();
o SimpleDateFormat format= new
SimpleDateFormat("dd/MM/yyyy");
o String str = format.format(d);
o S.o.p("Date : " + str );
o String str1 = "22/03/2009";
o Date d1 = format.parse(str1);
o S.o.p(d1);
 }
 Output
o String : 04/01/2010
o Sun Mar 22 00:00:00 IST 2009

66. Disclaimer
This is an educational presentation to enhance the
skill of computer science students.
This presentation is available for free to computer
science students.
Some internet images from different URLs are
used in this presentation to simplify technical
examples and correlate examples with the real
world.
We are grateful to owners of these URLs and
pictures.
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67. Thank You!
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