Java & advanced java

By,
Prof. Basavaraj M. Hunshal
Prof. Mahadev Immannavar
Dept. of Computer Science &
Engg.
JAVA & Advanced Java :
A Crash Course
KLE Society’s
KLE College of Engineering & Technology,
Chikodi.

Contents
"Write Once, Run Everywhere"
 Motivation
 Introduction to Object oriented Programming
Paradigm.
 How Java is different from C++?
 Java Program structure with simple examples.
 Tokens of Java Language
 Control statements.
 Arrays
 Classes and Objects
 Pillars of OOPs : Encapsulation, Polymorphism &
Inheritance.
2

Motivation
&
Applications of Java
"Write Once, Run Everywhere"3

 Java is one of the most popular programming languages used to
create Web applications and platforms. It was designed for flexibility,
allowing developers to write code that would run on any machine,
regardless of architecture or platform.
 According to Sun, more than 3 billion devices run java. There are
many devices where java is currently used. Some of them are as
follows:
 Desktop Applications such as acrobat reader, media player, antivirus
etc.
 Web Applications such as irctc.co.in, javatpoint.com etc.
 Enterprise Applications such as banking applications.
 Mobile
 Embedded System
 Smart Card
 Robotics
Reasons to Learn Java Programming
Language &
Why Java is Best ?
4

History of Java
 Computer language innovation and development occurs
for two fundamental reasons:
1) To adapt to changing environments and uses.
2) To implement improvements in the art of
programming.
 Many Java features are inherited from the earlier
languages:
B  C  C++  Java
 Designed by James Gosling, Patrick Naughton, Chris
Warth, Ed Frank and Mike Sheridan at Sun
Microsystems in 1991.
 The original motivation is not Internet: platform-
independent software embedded in consumer
electronics appliances.
5

Features of Java
 Simple - Syntax is based on C++.
 Object-Oriented - is a methodology that simplify software
development and maintenance by providing some rules.
 Platform Independent - Java code can be run on multiple
platforms e.g. Windows, Linux, Sun Solaris, Mac/OS etc. Java
code is compiled by the compiler and converted into bytecode.
This bytecode is a platform-independent code because it can be
run on multiple platforms i.e. Write Once and Run
Everywhere(WORE).
 Secured - Java is secured because:
 No explicit pointer
 Java Programs run inside virtual machine sandbox
6

 Robust- Robust simply means strong. Java uses strong
memory management. There are lack of pointers that avoids
security problem. There is automatic garbage collection in
java. There is exception handling and type checking
mechanism in java.
 Architecture Neutral- There is no implementation
dependent features e.g. size of primitive types is fixed.
 Portable - We may carry the java bytecode to any platform.
 High Performance - Java is faster than traditional
interpretation since byte code is "close" to native code
 Distributed - We may access files by calling the
methods from any machine on the internet.
 Multi-threaded - A thread is like a separate program,
executing concurrently. We can write Java programs that
deal with many tasks at once by defining multiple threads.
7

Generation of Computer
Languages

 OOP was introduced to overcome flaws in the
procedural approach to programming.
 Such as lack of reusability & maintainability.
 Fundamental idea behind object-oriented languages
is to combine into a single unit both data and the
functions that operate on that data. Such a unit is
called an object.
Introduction to OOPs
9

OOP -Concepts
 Data Abstraction — it is the act of representing the
essential features without including the background
details. Data Hiding- it is a related concept of data
abstraction. Unessential features are hidden from the
world.
 Data Encapsulation — it is the wrapping of data and
associated functions in one single unit.
 Inheritance — it is the capability of one class to
inherit properties from other class.
 Polymorphism — it is the ability for data to be
processed in more than one form.
 Modularity — it is the concept of breaking down the
program into several module. Erg. : Classes,
Structure, etc.
10

How Java is differ from C++ ?

What is Java?
• Java is a high level, robust, secured and object-oriented
programming language.
• Platform: Any hardware or software environment in which
a program runs, is known as a platform. Since Java has its
own runtime environment (JRE) and API, it is called
platform.
Simple Java Program -
class Simple
{
public static void main(String args[])
{
System.out.println("Hello Java");
}
}
12

Execution of a Java
Program -
13

 Tokens
 Keywords
 Identifiers
 Constants
 Operators
 Data types
Programming Elements in Java
Language
14

Keywords
15

 Java identifier names:
— first character must a letter or or $
— following characters can be any of those characters
or a number
— identifiers are case-sensitive; name is different from
Name
 Example Java identifiers:
olivia second_place _myName
belles’s 2%milk
kelly@yahoo.com
TheCure ANSWER IS 42 $variable
me+u :-) question?
side-swipe hi there ph.d
Identifiers
16

Operators in Java

• Program to get the data from user
• Java program to add two numbers
• Swapping using temporary or third variable
18

 Java defines eight simple types:
1) byte – 8-bit integer type
2) short – 16-bit integer type
3) int – 32-bit integer type
4) long – 64-bit integer type
5) float – 32-bit floating-point type
6) double – 64-bit floating-point type
7) char – symbols in a character set
8) boolean – logical values true and false
Data Types
19 "Write Once, Run Everywhere"

Java control statements cause the flow of execution to
advance and branch based on the changes to the
state of the program.
Control statements are divided into three groups:
1. selection statements allow the program to choose
different parts of the execution based on the
outcome of an expression
2. iteration statements enable program execution to
repeat one or more statements
3. jump statements enable your program to execute
in a non-linear fashion
Control Statements

 Java selection statements allow to control the
flow of program’s execution based upon
conditions known only during run-time.
 Java provides four selection statements:
1) if
2) if-else
3) if-else-if
4) switch
Selection Statements

 Java iteration statements enable repeated execution of
part of a program until a certain termination condition
becomes true.
 Java provides three iteration statements:
1) while
2) do-while
3) for
4) for each
Iteration Statements

 Java jump statements enable transfer of control to
other parts of program.
 Java provides three jump statements:
1) break
2) continue
3) return
 In addition, Java supports exception handling that
can also alter the control flow of a program.
Jump Statements
23

 Java program to check whether the given
number palindrome or not
 Java program to find the factorial of a given
number
24

Type Conversion
• Size Direction of Data Type
– Widening Type Conversion (Casting down)
• Smaller Data Type  Larger Data Type
– Narrowing Type Conversion (Casting up)
• Larger Data Type  Smaller Data Type
• Conversion done in two ways
– Implicit type conversion
• Carried out by compiler automatically
– Explicit type conversion
• Carried out by programmer using casting
25

• Widening Type Conversion
– Implicit conversion by compiler automatically
byte -> short, int, long, float, double
short -> int, long, float, double
char -> int, long, float, double
int -> long, float, double
long -> float, double
float -> double

• Narrowing Type Conversion
– Programmer should describe the conversion
explicitly
byte -> char
short -> byte, char
char -> byte, short
int -> byte, short, char
long -> byte, short, char, int
float -> byte, short, char, int, long
double -> byte, short, char, int, long, float

 byte and short are always promoted to int
 if one operand is long, the whole expression is
promoted to long
 if one operand is float, the entire expression is
promoted to float
 if any operand is double, the result is double
Type Conversion

 General form: (targetType) value
 Examples:
1) integer value will be reduced module bytes
range:
int i=10;
byte b = (byte) i;
2) floating-point value will be truncated to
integer
value:
float f=15.5;
int i = (int) f;
Type Casting

Arrays
 An array is a group of same-typed objects
referred by a common name, with individual
objects accessed by their index.
 Arrays are:
1) declared
2) created
3) initialized
4) used
 Also, arrays can have one or several dimensions.
30

 Array declaration involves:
1) declaring an array identifier
2) declaring the number of dimensions
3) declaring the data type of the array elements
 Two styles of array declaration:
type array-variable[];
or
type [] array-variable;
Array Declaration

 After declaration, no array actually exists.
 In order to create an array, we use the new
operator:
type array-variable[];
array-variable = new type[size];
 This creates a new array to hold size elements of
type type, which reference will be kept in the
variable array-variable.
Array Creation

 We can refer to the elements of this array through
their indexes:
 array-variable[index]
 The array index always starts with zero!
 The Java run-time system makes sure that all array
indexes are in the correct range, otherwise raises a
run-time error.
Array Indexing
Array
Initialization Arrays can be initialized when they are declared:
 int monthDays[] =
{31,28,31,30,31,30,31,31,30,31,30,31};
 Note:
1) there is no need to use the new operator
2) the array is created large enough to hold all specified
elements33 "Write Once, Run Everywhere"

 Multidimensional arrays are arrays of arrays:
1) declaration: int array[][];
2) creation: int array = new int[2][3];
3) initialization
int array[][] = { {1, 2, 3}, {4, 5, 6} };
Examples:
 Find Largest and Smallest Number in an Array
 Java program for linear search
 Java program for Binary search
 Java program to add two matrices
Multidimensional Arrays

 Real world objects are things that have:
1) state
2) behavior
Example: your dog:
 state – name, color, breed, sits?, barks?, wages
tail?, runs?
 behavior – sitting, barking, waging tail, running
 A software object is a bundle of variables (state)
and methods (operations).
What is an Object?

 A class is a blueprint that defines the variables and
methods common to all objects of a certain kind.
 Example: ‘your dog’ is a object of the class Dog.
 An object holds values for the variables defines in the
class.
 An object is called an instance of the Class
What is a Class?

 A variable is declared to refer to the objects of
type/class String:
String s;
 The value of s is null; it does not yet refer to any
object.
 A new String object is created in memory with
initial “abc” value:
 String s = new String(“abc”);
 Now s contains the address of this new object.
Object Creation

 A program accumulates memory through its
execution.
 Two mechanism to free memory that is no longer
need by the program:
1) manual – done in C/C++
2) automatic – done in Java
 In Java, when an object is no longer accessible
through any variable, it is eventually removed from
the memory by the garbage collector.
 Garbage collector is parts of the Java Run-Time
Environment.
Object Destruction

 A basis for the Java language.
 Each concept we wish to describe in Java must be
included inside a class.
 A class defines a new data type, whose values are
objects:
 A class is a template for objects
 An object is an instance of a class
Class

 A class contains a name, several variable declarations
(instance variables) and several method declarations. All
are called members of the class.
 General form of a class:
class classname
{
type instance-variable-1;
…
type instance-variable-n;
type method-name-1(parameter-list) { … }
type method-name-2(parameter-list) { … }
…
type method-name-m(parameter-list) { … }
}
Class Definition

class Box {
double width;
double height;
double depth;
}
class BoxDemo
{
public static void main(String args[])
{
Box mybox = new Box();
double vol;
mybox.width = 10;
mybox.height = 20;
mybox.depth = 15;
vol = mybox.width * mybox.height * mybox.depth;
System.out.println ("Volume is " + vol);
}
}
Example: Class Usage

 A constructor initializes the instance variables of an
object.
 It is called immediately after the object is created but
before the new operator completes.
1) it is syntactically similar to a method:
2) it has the same name as the name of its class
3) it is written without return type; the default
return type of a class
 constructor is the same class
 When the class has no constructor, the default
constructor automatically initializes all its instance
variables with zero.
Constructor
42

class Box
{
double width;
double height;
double depth;
Box()
{
System.out.println("Constructing Box");
width = 10; height = 10; depth = 10;
}
double volume()
{
return width * height * depth;
}
}
Example: Constructor

class Box {
double width;
double height;
double depth;
Box(double w, double h, double d)
{
width = w; height = h; depth = d;
}
double volume()
{
return width * height * depth;
}
}
Parameterized Constructor

 General form of a method definition:
type name(parameter-list)
{
… return value;
…
}
 Components:
1. type - type of values returned by the method. If a
method does not return any value, its return type
must be void.
2. name is the name of the method
3. parameter-list is a sequence of type-identifier lists
separated by commas
4. return value indicates what value is returned by the
method.
Methods

 Classes declare methods to hide their internal data
structures, as well as for their own internal use:
Within a class, we can refer directly to its member
variables:
class Box
{
double width, height, depth;
void volume()
{
System.out.print("Volume is ");
System.out.println(width * height * depth);
}
}
Example: Method

 Parameters increase generality and applicability
of a method:
1) method without parameters
int square() { return 10*10; }
2) method with parameters
int square(int i) { return i*i; }
 Parameter: a variable receiving value at the time
the method is invoked.
 Argument: a value passed to the method when it
is invoked.
Parameterized Method

Access Control: Data Hiding and
Encapsulation
• Java provides control over the visibility of variables and
methods.
• Encapsulation, safely sealing data within the capsule of the
class Prevents programmers from relying on details of class
implementation, so you can update without worry
• Helps in protecting against accidental or wrong usage.
• Keeps code elegant and clean (easier to maintain)

Access Modifiers: Public, Private, Protected
• Public: keyword applied to a class, makes it
available/visible everywhere. Applied to a method
or variable, completely visible.
• Private: fields or methods for a class only visible
within that class. Private members are not visible
within subclasses, and are not inherited.
• Protected: members of a class are visible within
the class, subclasses and also within all classes
that are in the same package as that class.

Visibility
public class Circle {
private double x,y,r;
// Constructor
public Circle (double x, double y, double r) {
this.x = x;
this.y = y;
this.r = r;
}
//Methods to return circumference and area
public double circumference() { return 2*3.14*r;}
public double area() { return 3.14 * r * r; }
}

Keyword “this”
• Can be used by any object to refer to itself in any
class method
• Typically used to
– Avoid variable name collisions
– Pass the receiver as an argument
– Chain constructors

 Keyword this allows a method to refer to the
object that invoked it.
 It can be used inside any method to refer to the
current object:
Box(double width, double height, double depth) {
this.width = width;
this.height = height;
this.depth = depth;
}

 Garbage collection is a mechanism to remove objects
from memory when they are no longer needed.
 Garbage collection is carried out by the garbage
collector:
1) The garbage collector keeps track of how many references
an object has.
2) It removes an object from memory when it has no longer
any references.
3) Thereafter, the memory occupied by the object can be
allocated again.
4) The garbage collector invokes the finalize method.
Garbage Collection

 A constructor helps to initialize an object just after
it has been created.
 In contrast, the finalize method is invoked just
before the object is destroyed:
 1) implemented inside a class as:
protected void finalize() { … }
 2) implemented when the usual way of removing
objects from memory is insufficient, and some
special actions has to be carried out
finalize() Method

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