Learn Java - Java Tutorial for Beginners - Java Tutorial

EASY WEB SOLUTION
Instructor: Lavi Gupta, 09803266066

 Instructor: LAVI GUPTA (M.Tech Computers)
◦ Office: 351 TriCity PLAZZA Adj. Sec-20
Panchkula
◦ Office Phone: 9803266066, 9501922388
◦ Email: techlavi@gmail.com
◦ Office hours: Monday To Fridays 10-7pm
Or by appointment call: 09803266066

 Lecture: MWF 01:00 PM – 02:10 PM
 Lab: W 02:30 PM - 04:20 PM

 Midterm: 20%
 Final: 25%
 Programming Projects: 40%
 Homework and labs: 15%

 Object-Oriented Software Development
◦ problem solving
◦ program design, implementation, and testing
◦ object-oriented concepts
 classes
 objects
 encapsulation
 inheritance
 polymorphism
◦ graphical user interfaces

•The Java Programming Language
•Program Development
•Object-Oriented Programming

 A programming language specifies the words
and symbols that we can use to write a program
 A programming language employs a set of rules
that dictate how the words and symbols can be
put together to form valid program statements
 The Java programming language was created by
Sun Microsystems, Inc.
 It was introduced in 1995 and it's popularity has
grown quickly since

 In the Java programming language:
◦ A program is made up of one or more classes
◦ A class contains one or more methods
◦ A method contains program statements
 These terms will be explored in detail
throughout the course
 A Java application always contains a method
called main

public class Lincoln
{
//-----------------------------------------------------------------
// Prints a presidential quote.
//-----------------------------------------------------------------
public static void main (String[] args)
{
System.out.println ("A quote by Abraham Lincoln:");
System.out.println ("Whatever you are, be a good one.");
}
}

public class MyProgram
{
}
// comments about the class
class header
class body
Comments can be placed almost anywher

public class MyProgram
{
}
// comments about the class
{
}
// comments about the method
method header
method body

 Comments in a program are called inline
documentation
 They should be included to explain the
purpose of the program and describe
processing steps
 They do not affect how a program works
 Java comments can take three forms:
// this comment runs to the end of the line
/* this comment runs to the terminating
symbol, even across line breaks */
/** this is a javadoc comment */

 Identifiers are the words a programmer uses in a
program
 An identifier can be made up of letters, digits, the
underscore character ( _ ), and the dollar sign
 Identifiers cannot begin with a digit
 Java is case sensitive - Total, total, and
TOTAL are different identifiers
 By convention, programmers use different case
styles for different types of identifiers, such as
◦ title case for class names - Lincoln
◦ upper case for constants - MAXIMUM

 The Java reserved words:
abstract
assert
boolean
break
byte
case
catch
char
class
const
continue
default
do
double
else
enum
extends
false
final
finally
float
for
goto
if
implements
import
instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
strictfp
super
switch
synchronized
this
throw
throws
transient
true
try
void
volatile
while

 Spaces, blank lines, and tabs are called
white space
 White space is used to separate words and
symbols in a program
 Extra white space is ignored
 A valid Java program can be formatted
many ways
 Programs should be formatted to enhance
readability, using consistent indentation

public class Lincoln2{public static void
main(String[]args){
System.out.println("A quote by Abraham
Lincoln:");
System.out.println("Whatever you are, be a
good one.");}}

The Java Programming Language
Program Development
Object-Oriented Programming

 The mechanics of developing a program
include several activities
◦ writing the program in a specific programming
language (such as Java)
◦ translating the program into a form that the
computer can execute
◦ investigating and fixing various types of errors
that can occur
 Software tools can be used to help with all
parts of this process

 Each type of CPU executes only a
particular machine language
 A program must be translated into
machine language before it can be
executed
 A compiler is a software tool which
translates source code into a specific
target language
 Often, that target language is the machine
language for a particular CPU type
 The Java approach is somewhat different

 The Java compiler translates Java source code
into a special representation called bytecode
 Java bytecode is not the machine language for
any traditional CPU
 Another software tool, called an interpreter,
translates bytecode into machine language and
executes it
 Therefore the Java compiler is not tied to any
particular machine
 Java is considered to be architecture-neutral

Java source
code
Machine
code
Java
bytecode
Bytecode
interpreter
Bytecode
compiler
Java
compiler

 There are many programs that support the
development of Java software, including:
◦ Sun Java Development Kit (JDK)
◦ Sun NetBeans
◦ IBM Eclipse
◦ Borland JBuilder
◦ MetroWerks CodeWarrior
◦ BlueJ
◦ jGRASP
 Though the details of these environments
differ, the basic compilation and execution
process is essentially the same

 The syntax rules of a language define how we
can put together symbols, reserved words, and
identifiers to make a valid program
 The semantics of a program statement define
what that statement means (its purpose or role
in a program)
 A program that is syntactically correct is not
necessarily logically (semantically) correct
 A program will always do what we tell it to do,
not what we meant to tell it to do

 A program can have three types of errors
 The compiler will find syntax errors and other basic
problems (compile-time errors)
◦ If compile-time errors exist, an executable version of the
program is not created
 A problem can occur during program execution,
such as trying to divide by zero, which causes a
program to terminate abnormally (run-time errors)
 A program may run, but produce incorrect results,
perhaps using an incorrect formula (logical errors)

errors
errors
Edit and
save program
Compile program
Execute program and
evaluate results

 The purpose of writing a program is to solve a
problem
 Solving a problem consists of multiple activities:
◦ Understand the problem
◦ Design a solution
◦ Consider alternatives and refine the solution
◦ Implement the solution
◦ Test the solution
 These activities are not purely linear – they
overlap and interact

 The key to designing a solution is breaking
it down into manageable pieces
 When writing software, we design separate
pieces that are responsible for certain parts
of the solution
 An object-oriented approach lends itself to
this kind of solution decomposition
 We will dissect our solutions into pieces
called objects and classes

 Java is an object-oriented programming language
 As the term implies, an object is a fundamental
entity in a Java program
 Objects can be used effectively to represent real-
world entities
 For instance, an object might represent a
particular employee in a company
 Each employee object handles the processing and
data management related to that employee

 An object has:
◦ state - descriptive characteristics
◦ behaviors - what it can do (or what can be done to it)
 The state of a bank account includes its
account number and its current balance
 The behaviors associated with a bank account
include the ability to make deposits and
withdrawals
 Note that the behavior of an object might
change its state

 An object is defined by a class
 A class is the blueprint of an object
 The class uses methods to define the behaviors
of the object
 The class that contains the main method of a
Java program represents the entire program
 A class represents a concept, and an object
represents the embodiment of that concept
 Multiple objects can be created from the same
class

Character Strings
Variables and Assignment
Primitive Data Types
Expressions
Data Conversion
Interactive Programs
Graphics
Applets
Drawing Shapes

 A string of characters can be represented as a
string literal by putting double quotes around
the text:
 Examples:
"This is a string literal."
"123 Main Street"
"X"
 Every character string is an object in Java,
defined by the String class
 Every string literal represents a String object

 In the Lincoln program from Chapter 1, we
invoked the println method to print a
character string
 The System.out object represents a
destination (the monitor screen) to which we
can send output
System.out.println ("Whatever you are, be a good one.");
object method
name
information provided to the method
(parameters)

 The System.out object provides another
service as well
 The print method is similar to the
println method, except that it does not
advance to the next line
 Therefore anything printed after a print
statement will appear on the same line

public class Countdown
{
//-----------------------------------------------------------------
// Prints two lines of output representing a rocket countdown.
//-----------------------------------------------------------------
{
System.out.print ("Three... ");
System.out.print ("Two... ");
System.out.print ("One... ");
System.out.print ("Zero... ");
System.out.println ("Liftoff!"); // appears on first output line
System.out.println ("Houston, we have a problem.");
}
}

 The string concatenation operator (+) is
used to append one string to the end of
another
"Peanut butter " + "and jelly"
 It can also be used to append a number to a
string
 A string literal cannot be broken across two
lines in a program

public class Facts
{
{
// Strings can be concatenated into one long string
System.out.println ("We present the following facts for your "
+ "extracurricular edification:");
System.out.println ();
// A string can contain numeric digits
System.out.println ("Letters in the Hawaiian alphabet: 12");
// A numeric value can be concatenated to a string
System.out.println ("Dialing code for Antarctica: " + 672);
System.out.println ("Year in which Leonardo da Vinci invented "
+ "the parachute: " + 1515);
System.out.println ("Speed of ketchup: " + 40 + " km per year");
}
}

 The + operator is also used for arithmetic
addition
 The function that it performs depends on the
type of the information on which it operates
 If both operands are strings, or if one is a string
and one is a number, it performs string
concatenation
 If both operands are numeric, it adds them
 The + operator is evaluated left to right, but
parentheses can be used to force the order

public class Addition
{
//-----------------------------------------------------------------
// Concatenates and adds two numbers and prints the
results.
//-----------------------------------------------------------------
{
System.out.println ("24 and 45 concatenated: " + 24 +
45);
System.out.println ("24 and 45 added: " + (24 + 45));
}
}

 What if we wanted to print a the quote
character?
 The following line would confuse the compiler
because it would interpret the second quote as
the end of the string
System.out.println ("I said "Hello" to you.");
 An escape sequence is a series of characters
that represents a special character
 An escape sequence begins with a backslash
character ()
System.out.println ("I said "Hello" to you.");

 Some Java escape sequences:
Escape Sequence
b
t
n
r
"
'

Meaning
backspace
tab
newline
carriage return
double quote
single quote
backslash

public class Roses
{
//-----------------------------------------------------------------
// Prints a poem (of sorts) on multiple lines.
//-----------------------------------------------------------------
{
System.out.println ("Roses are red,ntViolets are blue,n" +
"Sugar is sweet,ntBut I have "commitment issues",nt"
+
"So I'd rather just be friendsntAt this point in our " +
"relationship.");
}
}

 A variable is a name for a location in memory
 A variable must be declared by specifying the
variable's name and the type of information
that it will hold
int total;
int count, temp, result;
Multiple variables can be created in one declaration
data type variable name

 A variable can be given an initial value in the
declaration
• When a variable is referenced in a program, its
current value is used
int sum = 0;
int base = 32, max = 149;

public class PianoKeys
{
//-----------------------------------------------------------------
// Prints the number of keys on a piano.
//-----------------------------------------------------------------
{
int keys = 88;
System.out.println ("A piano has " + keys + " keys.");
}
}

 An assignment statement changes the value of
a variable
 The assignment operator is the = sign
total = 55;
• The value that was in total is overwritten
• You can only assign a value to a variable that is
consistent with the variable's declared type
• The expression on the right is evaluated and the
result is stored in the variable on the left

public class Geometry
{
{
int sides = 7; // declaration with initialization
System.out.println ("A heptagon has " + sides + " sides.");
sides = 10; // assignment statement
System.out.println ("A decagon has " + sides + " sides.");
sides = 12;
System.out.println ("A dodecagon has " + sides + " sides.");
}
}

 A constant is an identifier that is similar to a
variable except that it holds the same value
during its entire existence
 As the name implies, it is constant, not variable
 The compiler will issue an error if you try to
change the value of a constant
 In Java, we use the final modifier to declare a
constant
final int MIN_HEIGHT = 69;

 Constants are useful for three important reasons
 First, they give meaning to otherwise unclear
literal values
◦ For example, MAX_LOAD means more than the literal 250
 Second, they facilitate program maintenance
◦ If a constant is used in multiple places, its value need
only be updated in one place
 Third, they formally establish that a value should
not change, avoiding inadvertent errors by other
programmers

For online classes, contact: 9803266066
Skype: lavigupta18
Email: techlavi@gmail.com

Learn Java - Java Tutorial for Beginners - Java Tutorial

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