Introduction To Java

Computer Languages are evolve for two reasons

* to adapt to changes in environment and to implement advances

in the art of programming.

Java :-

...........

* It was conceived by James Gosling,Patrick Naughton,Chris Warth,Ed Frank and Mike Sheridan at Sun Microsystems,Inc in 1991.

* Initially called Oak it was renamed Java in 1995

* Primary aim is Platform Independent(architecture neutral)

- used to produce code that would run on a variety of CPUs under different environments

* Used to create software to be embedded in various electronic devices such as microwave ovens and remote controls.

* Internet version of C++

* Used to create two types of programs

1)Application 2)Applet

Application

--------------

It is a program that runs on your computer, under the Operating system of that computer.

Applet

---------

* It is a program that can react to user input and dynamically change.

True Object Oriented Programming Language

Machine code:

*************

*)Platform dependent

*)The machine can directly execute the code

Byte codes:

***********

It is a highly optimized set of instructions designed to be executed by the Java run-time system, which is called the Java Virtual Machine(JVM).

* Platform independent

* JVM(Java Virtual Machine) which is platform independent

Java Features:-

****************

Compiled and Interpreted

Platform Independent and portable

Object oriented

robust(program must execute reliably in a variety of systems) and secure

distributed technology[Client & Server Model]

MultiThreading ( allows you to write programs that do many things simultaneously)

Architecture-Neutral - "write once; run anywhere,any time, forever"

C and Java

....................

· Java does not include the C unique statement keywords sizeof and typedef.

· Java does not contain the data types struct and union.

· Java does not define the type modifiers keywords auto,extern,register,signed and unsigned.

· Java does not support an explicit pointer type.

· Java does not have a preprocessor and therefore we cannot use #define,#include, and #ifdef statements.

· Java requires that the functions with no arguments must be declared with empty paranthesis and not with the void keyword as done in c.

· Java adds new operators such as instanceof and >>>.

· Java adds labelled break and continue statements.

c++ and Java :-

..........................

· Java does not support operator overloading.

· Java does not have template classes as in C++.

· Java does not support multiple inheritance of classes.This is accomplished by using a new feature called interface.

· Java does not use pointers.

· Java has replaced the destructor function with a finalize() function.

· There are no header files in java

JDK Environment :-(Java Developer toolKit)

***************

javac java Compiler(Translates Java sourcecode to Byte code)

java Interpreter(Byte code to Machine code)

javap disassembler

javah Java Headerfile

javadoc Java Documentation files

jdb Java Debugger

AppletViewer run the Applet Files

API:-(Application Programming Interface) :

- API is a set of classes and interfaces that support operations

on collections of objects.

import java.io.*;

import.java.lang.*;

* -> is a package(means collection of classes and Interfaces)

lang

util

net

sql

awt

applet

eg:-

javap java.lang.System

To Compile Java File:-

*********************

javac filename.java

eg:

----

javac Demo.java

(to create Class file)

To run:-

******

java classname

---

java Demo

Datatypes

----------

Integers:

byte - 8 bits

short - 16 bits

int - 32 bits

long - 64 bits

Float:

float - 32 bits

double - 64 bits

Character:

char - 16 bits

String

Boolean:

boolean - returns true or false

General format of a java program

--------------------------------------

class classname

{

public static void main(String args[ ])

{

statements;

}

output statement

---------------------

System.out.print("sum"+a);

System.out.println("Message");

Input

-----

types

1)Keyboard input

2)through command line arguments

3)interactive input method

--------

identifiers must start with $, _, or a letter.

import java.io.*;

class Test

{

public static void main(String args[])

{

System.out.println("Hello");

System.out.println("Java");

}

import java.io.*;

class Test

{

public static void main(String args[])throws IOException

{

int a=100;

float b=123.34f;

char c='s';

System.out.println("a="+a);

System.out.println("b="+b);

System.out.println("c="+c);

}

import java.io.*;

class Test

{

public static void main(String args[])throws IOException

{

int a=100;

float b=123.34f;

char c='s';

System.out.println("a="+a);

System.out.println("b="+b);

System.out.println("c="+c);

}}

Reading data from Keyboard

-----------------------------------

import java.io.*;

class Test

{

public static void main(String args[])throws IOException

{

DataInputStream in=new DataInputStream(System.in);

int a;

float b;

char c;

String d;

System.out.println("Enter a String :");

d=(in.readLine());

System.out.println("Enter Integer value:");

a=Integer.parseInt(in.readLine());

System.out.println("Enter Float value");

b=Float.valueOf(in.readLine()).floatValue();

System.out.println("Enter a Character :");

c=(char)System.in.read();

System.out.println("a="+a+"\nb="+b+"\nc="+c+"\nd="+d);

}

import java.io.*;

class Test

{

public static void main(String args[])throws IOException

{

DataInputStream in=new DataInputStream(System.in);

double d;

System.out.println("Enter Double value :");

d=Double.parseDouble(in.readLine());

System.out.println("d="+d);

}

import java.io.*;

import java.lang.*;

class Test

{

public static void main(String args[])throws IOException

{

DataInputStream in=new DataInputStream(System.in);

String name;

int m1,m2,m3;

float tot,avg;

System.out.println("Enter Your Name :");

name=in.readLine();

System.out.println("Enter 3 Marks :");

m1=Integer.parseInt(in.readLine());

m2=Integer.parseInt(in.readLine());

m3=Integer.parseInt(in.readLine());

tot=m1+m2+m3;

avg=tot/3;

System.out.println("Name="+name+"\nTotal="+tot+"\nAverag="+avg);

}

class sum//keyboard input

{

public static void main(String args[])

{

int a=20,b=30;

System.out.println("Sum="+(a+b));

}

class sum//Commandline arguments

{

public static void main(String args[])

{

int a,b;

a=Integer.parseInt(args[0]);

b=Integer.parseInt(args[1]);

System.out.println("Sum="+(a+b));

}

import java.io.*;

class sum//Interactive Input Method

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int a,b;

System.out.println("Enter 2 numbers :");

a=Integer.parseInt(din.readLine());

b=Integer.parseInt(din.readLine());

System.out.println("Sum="+(a+b));

}

import java.io.*;

import java.lang.*;

class Exam

{

public static void main(String args[])throws IOException

{

int a=9;

System.out.println("Sqrt(9)="+Math.sqrt(a));

System.out.println("pow(a,2)="+Math.pow(a,2));

}

Simple if else

========

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int a;

System.out.println("Enter a number");

a=Integer.parseInt(din.readLine());

if(a%2==0)

System.out.println("Even Number");

else

System.out.println("Odd Number");

}

Biggest between 3 numbers

---------------------------------

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int a,b,c;

System.out.println("Enter 3 number");

a=Integer.parseInt(din.readLine());

b=Integer.parseInt(din.readLine());

c=Integer.parseInt(din.readLine());

if(a>b)

{

if(a>c)

System.out.println("A is big");

else

System.out.println("C is big");

}

else

{

if(b>c)

System.out.println("B is big");

else

System.out.println("C is big");

}

else if ladder

---------------

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

String name;

int m1,m2,m3,tot,avg;

char g;

System.out.println("Enter a name");

name=(din.readLine());

System.out.println("Enter 3 Marks :");

m1=Integer.parseInt(din.readLine());

m2=Integer.parseInt(din.readLine());

m3=Integer.parseInt(din.readLine());

tot=m1+m2+m3;

avg=(tot)/3;

if(avg>=80&&avg<=100)

g='A';

else if(avg<80&&avg>=60)

g='B';

else if(avg<60&&avg>=40)

g='C';

else if(avg<40&&avg>=35)

g='D';

else

g='F';

System.out.println("Name="+name+"\nTotal="+tot+"\nAverage="+avg+"\nGrade="+g);

}

Using switch case

---------------------

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int a,b,c;

System.out.println("1.Sum\n2.Sub\n3.Mul\n4.Div\n5.Mod\nenter your choice");

c=Integer.parseInt(din.readLine());

System.out.println("Enter 2 numbers :");

a=Integer.parseInt(din.readLine());

b=Integer.parseInt(din.readLine());

switch(c)

{

case 1:

System.out.println("Sum="+(a+b));

break;

case 2:

System.out.println("Sub="+(a-b));

break;

case 3:

System.out.println("Mul="+(a*b));

break;

case 4:

System.out.println("Div="+(a/b));

break;

case 5:

System.out.println("Mod="+(a%b));

break;

default:

System.out.println("Not in case");

}

import java.io.*;

class selectcase

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

char ch;

System.out.println("Enter a character r/g/b:");

ch=(char)System.in.read();

switch(ch)

{

case 'r':

case 'R':

System.out.println("Red");

break;

case 'g':

case 'G':

System.out.println("Green");

break;

case 'b':

case 'B':

System.out.println("Blue");

break;

default:

System.out.println("Invalid");

}

Example program for while Find the digit sum

-----------------------------------------------------

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int n,s=0;

System.out.println("Enter a number :");

n=Integer.parseInt(din.readLine());

while(n>0)

{

s=s+(n%10);

n/=10;

}

System.out.println("Digit sum="+s);

}

Armstrong or not

---------------------

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int n,s=0,a,r;

System.out.println("Enter a number :");

n=Integer.parseInt(din.readLine());

a=n;

while(n>0)

{

r=n%10;

s=s+r*r*r;

n/=10;

}

if(s==a)

System.out.println("Armstrong");

else

System.out.println("Not Armstrong");

}

do while

========

syntax:

{

statement;

}while(condition);

//Find the sum of given numbers using do while

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int n,s=0,i=1,c;

System.out.println("How many numbers you want to give :");

c=Integer.parseInt(din.readLine());

{

System.out.println("Enter a number :");

n=Integer.parseInt(din.readLine());

s=s+n;

i++;

}while(i<=c);

System.out.println("Sum of given numbers="+s);

}

for

===

syntax:

for(initialization;condition;increment or decrement)

{

statement;

}

Factorial value

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int n,f=1,i;

System.out.println("Enter a number :");

n=Integer.parseInt(din.readLine());

for(i=1;i<=n;i++)

f=f*i;

System.out.println("Factorial value="+f);

}

Table

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int n,i;

System.out.println("Enter Table Number :");

n=Integer.parseInt(din.readLine());

for(i=1;i<=15;i++)

System.out.println(i+"*"+n+"="+i*n);

}

Nested for loop

syntax:

for(initialization;condition;increment or decrement)

{

statement;

for(initialization;condition;increment or decrement)

{

statement;

}

Print the following triangle

1 2

1 2 3

1 2 3 4

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int n,i,j;

System.out.println("How many rows :");

n=Integer.parseInt(din.readLine());

for(i=1;i<=n;i++)

{

System.out.print("\n");

for(j=1;j<=i;j++)

System.out.print(j+"\t");

}

***

*****

*******

import java.io.*;

class sum

{

public static void main(String args[])throws IOException

{

DataInputStream din=new DataInputStream(System.in);

int i,j,n,k;

System.out.println("How many rows :");

n=Integer.parseInt(din.readLine());

for(i=1;i<=n;i++)

{

System.out.print("\n");

for(k=1;k<=n-i;k++)

System.out.print(" ");

for(j=1;j<=2*i-1;j++)

System.out.print("*");

}

Jump Statements:

===============

break, continue and return

Using break to Exit a loop

=========================

we can force immediate termination of a loop,by passing the

conditional expression and any remaining code in the body of the

loop.

ex:

import java.io.*;

class sum

{

public static void main(String args[])

{

for(int i=1;i<200;i++)

{

if(i==10)

break;

System.out.println("i: "+i);

}

System.out.println("Loop Complete.");

}

continue

========

continue statement causes control to be transferred directly to

the conditional expression that controls the loop.

ex:

import java.io.*;

class sum

{

public static void main(String args[])

{

for(int i=0;i<10;i++)

{

System.out.print(i+" ");

if(i%2==0)

continue;

System.out.print("\n");

}

import java.io.*;

class sum

{

public static void main(String args[])

{

for(int i=0;i<=10;i++)

{

if(i%2==1)

continue;

System.out.println(i);

}

return

========

The return statement immediately terminates the method in which it

is executed.

import java.io.*;

class sum

{

public static void main(String args[])

{

boolean t=true;

System.out.println("Before the return.");

if(t)

return;

System.out.println("This won't execute.");

}

========

class SumAvgNot

{

public static void main(String args[])

{

int sum=0;

for(int i=0;i<args.length;i++)

sum+=args[i];

System.out.println("Sum is :"+sum);

System.out.println("Average is :"+(float)sum/args.length);

}

error

S:\Selvarani\JAVA\Javaclass\Loops\SumavgNot.java:7: inconvertible types

found : java.lang.String

required: int

sum+=args[i];

1 error

Tool completed with exit code 1

--------

class Sumavg

{

public static void main(String args[])

{

int sum=0;

for(int i=0;i<args.length;i++)

sum+=Integer.parseInt(args[i]);

System.out.println("Sum is :"+sum);

System.out.println("Average is :"+(float)sum/args.length);

}

Java conditional statements

==============================

Simple if

---

if(condition)

{

statement;

}

--------

class app

{

public static void main(String args[])

{

int value=10;

if(value>0)

System.out.println("value="+value);

}

--------------

The if else statement

-------------------

if(condition)

statement;

else

statement;

class app1

{

public static void main(String args[])

{

int value=-10;

if(value>0)

System.out.println("Abs("+value+")="+value);

else

System.out.println("Abs("+value+")="+ -value);

}

Nested if statements:

=====================

class app2

{

public static void main(String args[])

{

double value=5;

if(value!=0){

if(value>0)

System.out.println("The result="+(1/value));

else

System.out.println("The result ="+(-1/value));

}

--------------------

The if-else ladders

---------------

class app3

{

public static void main(String args[])

{

String day="Wednesday";

if(day=="Monday")

System.out.println("It's Monday");

else if(day=="Tuesday")

System.out.println("It's Tuesday");

else if(day=="Wednesday")

System.out.println("Wednesday");

else if(day=="Thursday")

System.out.println("Thursday");

else if(day=="Friday")

System.out.println("Friday");

else if(day=="Saturday")

System.out.println("Saturday");

else if(day=="Sunday")

System.out.println("Sunday");

}

--------------------

The switch Statement

-------------------------

switch(expression)

case value1:

statement;

break;

case value2:

statement;

break;

case value3:

statement;

default:

default_statement;

}

Here, the value of expression, which must be of type byte,char,short, or int.

class app4

{

public static void main(String args[])

{

int day=3;

switch(day){

case 0:

System.out.println("It's Monday");

break;

case 1:

System.out.println("It's Tuesday");

break;

case 2:

System.out.println("Wednesday");

break;

case 3:

System.out.println("Thursday");

break;

case 4:

System.out.println("Friday");

break;

case 5:

System.out.println("Saturday");

break;

case 6:

System.out.println("Sunday");

break;

default:

System.out.println("Invalid");

}

------------------

The While Loop

----------------

general form

-----------

while(condition)

statement;

if condition is not true,the body of the loop is not even executed once.

//Display 10 to 1

class app5

{

public static void main(String args[])

{

int value=10;

while(value>0)

System.out.println("Current value="+value--);

}

//Find the factorial value

class app5

{

public static void main(String args[])

{

int value=5,factorial=1,temp;

temp=value;

while(temp>0)

{

factorial*=temp;

temp--;

}

System.out.println(value+"!="+factorial);

}

-------------------

The do-while Loop

---------------------

The do-while loop is just like a while loop,except that the test condition is evaluated at the end of the loop, not at the beginning.

general form

do{

statement

}while(condition);

The biggest reason to use a do-while loop instead of a while loop is when we need the body of the loop to be run at least once.

On the other hand, there are times when we should use a while loop instead of a do-while loop- when the body of the loop shouldn't even run once if the condition is not true.

class app5

{

public static void main(String args[])

{

double value=0;

do{

System.out.println("Ans="+1/value);

}while(value>0);

}

The for Loop

--------------

general form

---------------

for(initialization;condition;increment or decrement)

statement;

class app8

{

public static void main(String args[])

{

int i;

for(i=1;i<=10;i++)

System.out.println(i);

}

---------------

we don't have to give a for loop any body at all - in fact, we can use a null statement.

class app9

{

public static void main(String args[])

{

int i,sum=0;

for(i=0;i<=5;sum+=i,i++);

System.out.println("Sum of first 10 numbers="+sum);

}

---------------------

class app_10

{

public static void main(String args[])

{

int value=6,factorial=1,temp;

temp=value;

for(;temp>0;)

factorial*=temp--;

System.out.println(value+"!="+factorial);

}

-------------------

Nested Loops

================

syntax:

for(initialization;condition;increment or decrement)

{

for(initialization;condition;increment or decrement)

statement;

}

class app_11

{

public static void main(String args[])

{

int i,j;

for(i=1;i<=4;i++)

{

System.out.println();

for(j=1;j<=i;j++)

System.out.print(i+"\t");

}

-------------------

class app_12

{

public static void main(String args[])

{

int i,j;

for(i=1;i<=4;i++)

{

System.out.println();

for(j=i;j<=4;j++)

System.out.print(". ");

}

------------------------

Jump Statement

================

break,continue, and return.

These statements transfer control to another part of our program.

Using break

--------------

1. It terminates a statement sequence in a switch statement.

2. It can be used to exit a loop.

Using break to Exit a Loop

class app_13

{

public static void main(String args[])

{

int i;

for(i=1;i<=40;i++)

{

if(i==10)

break;

System.out.println("i :"+i);

}

System.out.print("Loop complete.");

}

Using continue

----------------

A continue statement causes control to be transferred directly to the conditional expression that controls the loop.

class app_14

{

public static void main(String args[])

{

int i;

for(i=0;i<10;i++)

{

System.out.print(i+" ");

if(i%2==0)

continue;

System.out.println("");

}

return

--------

The return statement is used to explicitly return from a method.

class app_15

{

public static void main(String args[])

{

boolean t=true;

System.out.println("Before the return");

if(t)

return;

System.out.println("This won't execute.");

}

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Sunday, April 1, 2012