JAVA PROGRAMMING

JAVA PROGRAMMING
Mr.M.S.N.MURTY,
ASSISTANT PROFESSOR,
DEPARTMENT OF CSE,

UNIT-1
• PROGRAM STRUCTURE IN JAVA
• INTRODUCTION
• WRITING SIMPLE JAVA PROGRAM
• JAVA STATEMENTS
• COMMAND LINE ARGUMENTS
• USER INPUT TO PROGRAMS

INTRODUCTION
• JAVA Is an object oriented programming Language.
• Initially it was OAK in 1991,later renamed as Java.
• Introduced by James Gosling in 1995
• Sun Microsystems released the first version in1996
as Java1.0.
• Adopted features from C and C++.
• Features include Simple, Platform Independent,
Portable, Robust, Secured, Multi Threaded, Object-
Oriented
• Supports all OOPs Concepts
I

Java Programming- Set up
• If we want to write , execute and run our java
programs, we need to install jdk software.
• We have to set two environment variables
PATH and CLASSPATH.
• JDK will be installed inside program files of your C
drive
• JDK can be downloaded from the site:
https://www.oracle.com/java/technologies/downlo
ads/

PATH and CLASSPATH
• PATH tells the operating system which
directories(folders) to search for executable files,
in response to commands issued by a user .
• CLASSPATH is a parameter which tells the JVM or
the Compiler, where to locate classes that are not
part of Java Development ToolKit(JDK).

Structure of a Simple Java Program
• Documentation Section
• Package Statement
• Import Statement
• Interface Section
• Class Definition
• Main Method Class

Structure of a Java Program….

Structure of a Java Program
• Documentation Section:
– Consists of comments which are useful to
understand the program statements/blocks
easily.
– Not part of the program i.e not executable ones.
– Compiler skips if comments encountered
– Both single line and multi line comments used.
– Can be used any where throughout the
program.

Comments contd..
• Single line Comments:
// denotes the single line comments
• Multi Line Comments:
/*a multi-line comment is declared like this
and can have multiple lines as a comment*/

Package Statement
• A package is a collection of similar classes
and
interfaces in Java.
• Package statement is used to define a new
package.
Syntax:
Package package_name;

Import Statement
• Java has a vast library(API)
• Java library contains hundreds of packages
• Import statement is used to import a
predefined package to utilize the classes and
interfaces of that package.
Syntax: import package_name;
eg: import java.util.*;
keyword
Package
name

Class Definition
• Class definition contains instance variables and instance
methods.
• Class definition provides the structure for the real
objects
• A java program can contain more classes.
Syntax:
class class_name
{
//instance variable declarations;
//instance method_defintions
}

Sample java program
import java.lang.*;
class Sample //class definition
{
public static void main(String arg[])
{
System.out.println("Welcome to JAVA!");
}
}
/*this program displays “Welcome to JAVA!” on
the console*/

Sample java program
Main method:
main() method is the starting point of a Java
program.
public static void main()
• public, means that it can be used outside of this class
as well.
• static means that we want to access a method
without making its objects. As we call the main
method without creating any objects.
• void indicates that it does not return any value. The
main is declared as void because it does not return
any value.

Compiling and Executing Java
Program
• Compiling the code using “javac”
C:javac filename.java
• Executing and Running the code
C:java classname

Command Line Arguments
java Simple <argument1> <argument2>….<argument-
n>
We can access these arguments in our program, using String
Array that we passed to the main method as –String arg[]
arg[0] arg[1] arg[n]
. . . .

Command Line Arguments
class Simple
{
public static void main(String[] args)
{
int i1 = Integer.parseInt(args[0]);
int i2 = Integer.parseInt(args[1]);
System.out.println(i1+i2);
}
}
When we compile the above code successfully and execute it
as Java Simple 10 20, the output will be :
30

Tokens in Java
A smallest individual unit in Java
The compiler breaks lines into pieces of text known as
Java tokens.
Java supports 5 types of tokens
• Keywords
• Identifiers
• Operators
• Literals
• Special Symbols

Keywords
• Reserved words, defined by the language
• Which have fixed meaning
• Compiler can recognize keywords only
Ex:
abstract,
for,do,while,switch,case,int,boolean,
Float,double,try,catch,final,finally,super,this
etc..

Identifiers
• User defined words
• Can be used for naming variables,program title,
method, class,package,interface etc..
• Following rules to be followed:
– The first letter of an identifier must be a letter,
underscore and dollor sign ($). It cannot be start
with a digit.Example: Abc1$23__23abc$$abc123
– Identifiers cannot contain whitespace.
– Identifiers in java are case-sensitive.
– Keywords cannot use as an identifiers.

Literals
• Are constants, i.e whose values are not changed.
• There are five types of literals in Java:
Integer: numbers without decimal point.
Example: -9, 0, 10, 0x11, 0xAA etc.
Floating Point: These are the numbers having
decimal part.
Example -10.2, 0, 100.99 etc.
Boolean:
Boolean literal are either TRUE or FALSE

Literals contd..
String:
A string literal is a sequence of characters
enclosed in double quotes.
Eg: “Welcome to JAVA”
Character:A character literal is a symbol
enclosed in single quotes.
Eg: ‘ * ’,’ N ’,’ $ ’,’ 9 ’

Special Symbols
• It is a set of few characters which have special
meaning known to Java compiler and cannot be
used by any other purpose.
Ex: [], {}, (), ;,.,*,= etc..
• Square Brackets []: It is used to defined array
element reference.
• Parentheses(): These special symbol are used to
call the functions and parameters.
• Braces{}: This indicates the starting and ending
of the code.

JAVA PROGRAMMING

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