JAVA PROGRAMMING

BASICS OF JAVA PROGRAMMING
Mugabe N. Gabriel

1

1. INTRODUCTION




Since the invention of
the computer, many
programming approaches have been tried.
These
include techniques such modular programming, topdown programming, bottom-up programming and
structured programming. The primary motivation in
each case has been the concern to handle the
increasing complexity of programs that are reliable and
maintainable.
With the advent of languages such C, structured
programming became very popular and was the
paradigm of the 1980s. Structured programming proved
to be a powerful tool that enable programmers to write
moderately complex programs fairly easily. However, as
programs grew larger, even the structured approach
failed to show the desired results in terms of bug-free,
easy-to-maintain and reusable programs.
2

INTRODUCTION CONT‟D


Object Oriented programming (OOP) is an approach
to program organization
and development which
attempts to eliminate some of the pitfalls of conventional
programming methods by incorporating the best of
structured programming features with several new
concepts. It is a new way of organizing and developing
programs and has nothing to do with any particular
language. However, not all languages are suitable to
implement the OOP concepts easily. Languages that
support OOP features include Smaltalk, Objective C,
C++ and Object Pascal. JAVA a pure OO language, is
one of the recent languages added to the list, the latest
one being C#.

3

Object-Oriented Paradigm
 The major objective of object-oriented approach is
to eliminate some of the flaws encountered in the
procedural approach. OOP treats data as a critical
element in the program development ad does not
allow it to flow freely around the system. It ties data
more closely to the functions that operate on it and
protects it from unintentional modification by other
functions. OOP allows us to decompose a problem
into a number of entities called Objects and then
build data and functions (known as methods in
Java) around these entities. The combination of
data and methods make up an object.


4



Object= Data+Methods

Method

Method

DATA
Method

Method

5



Features of OO paradigm are:









Emphasis on data rather than procedure;
Programs are divided into Objects
Data structures are designed to characterize the objects
Methods operating on the data of an object are tied
together in the data structure
Data is hidden and cannot be accessed by external
functions
Objects may communicate through methods
New data and methods can be easily added when
necessary
Bottom-up approach in program design

6



OO Programming is:


An approach that provides a way of modularizing
programs by creating partitioned memory area for both
data and functions that can be used as templates for
creating copies of such modules on demand.

7




Basic Concepts of Object-Oriented Programming:
Objects and Classes:
Objects are the basic runtime entities in an object- oriented
system. They may represent a person, a place, a bank account,
a table of data or any item that the program may handle. They
may represent also user- defined data types such as vectors
and lists. Objects should be chosen such that they match
closely with real world objects.
 When a program is executed, the objects interact by sending
messages to one another. For instance, „customer‟ and
„account‟ are two objects in banking program, then the customer
object may send a message to the account object requesting for
the balance. Each object contains data and code to manipulate
data. Objects can interact without having to know the details of
each other‟s data or code. The figure below shows a notation
that is popularly used to represent an object in object-oriented
analysis and design:


8

Object

Person
Name

Data

Basic Pay
Salary()

Methods

Tax()

This is representation of an Object

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


Basic Concepts of Object-Oriented Programming:
Objects and Classes:


The entire set of data and code of an abject can be made a
user-defined data type using the concept of a class. A class
may be thought of as a “data type” and an objet as a “variable”
of that data type. Once a class has been defined, someone can
create any number of objects belonging to that class. Each
object is associated with the data of type class with which they
are created. A class is thus a collection of objects of similar
type. For example, mango, apple and orange are members of
the class fruit. Classes are user-defined data types and behave
like the built-in types of a programming language. If fruit has
been defined as a class, then the statement fruit mango will
create an object mango belonging to the class fruit.
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

Data Abstraction and Encapsulation:


The wrapping up of data and methods into a single
unit(called class) is known as encapsulation. Data
encapsulation is the most striking feature of a class. The
data is not accessible to the outside world and only those
methods, which are wrapped in the class, can access it.
These methods provide the interface between the object‟s
data and the program. This insulation of the data from
direct access by the program is called data hiding.
Encapsulation makes it possible for objects to be treated
like “black boxes” each performing a specific task without
any concern for internal implementation. See the figure
below:
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Information “in”

Data
and
Method

Information “out”

Encapsulation– Objects as “black boxes”

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



Abstraction refers to the act of representing essential features
without including the background details or explanation. Classes
use the concept of abstraction and are defined as a list of abstract
attributes such as size, weight and cost, and methods that operate
on these attributes. They encapsulate all the essential properties of
the objects that are to be created.

Inheritance:


Inheritance is the process by which objects of one class acquire the
properties of objects of another class. Inheritance supports the
concept of hierarchical classification. For instance, the bird robin is a
part of the class flying bird, which is again a part of the class bird. In
the figure below, the principle behind this sort of division is that each
derived class shares common characteristics with the class from
which it is derived.
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Bird
Inheritance

Attributes:
Feathers
Lay eggs
Non flying
Bird

Flying Bird

Attributes:
-------------------------------

Attributes:
-----------------------------

Robin
Attributes:
-----------------------------

Swallow

Penguin

Attributes:
-----------------------------

Attributes:
-----------------------------

Kiwi
Attributes:
-----------------------------

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

Polymorphism:


Polymorphism is another important OOP concept. It
means the ability to take more than one form. For
example, an operation may exhibit different behaviour in
different instances, The behaviour depends upon the
types of data used in he operation. For instance,
consider the operation of addition. For two numbers, the
operation will generate a sum. If the operands are
strings, then the operation would produce a third string
by concatenation. This is something similar to a
particular word having several different meanings
depending on the context.
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Shape

Draw ( )

Circle Object

Box Object

Triangle Object

Draw (circle)

Draw (box)

Draw (triangle)

Polymorphism

16



Dynamic Binding:


Binding refers to the linking of a procedure call to the
code to be executed in response to the call. Dynamic
binding means that the code associated with a given
procedure call is not known until the time of the call at
runtime. It is associated with polymorphism and
inheritance

17



Benefits of OOP:











Through inheritance, it is possible to eliminate redundant code and
extend the use of existing classes;
Possibility of building programs from the standard working modules that
communicate with one another,
The principle of data hiding helps the programmer to build secure
programs that cannot be invaded by code in other parts of the program
It is possible to have multiple objects to coexist without any interference
It is possible to map objects in the problem domain to those objects in the
program
It is easy to partition he work in a project based on objects
The data-centered design approach enables us to capture more details of
model in an implementable
OO systems can be easily upgraded from small to large systems
Message passing techniques for communication between objects make
the interface descriptions with external systems much simpler
Software complexity can be easily managed

18

Application of OOP:
 The promising areas for application of OOp
includes:













Real-time systems
Simulation and modeling
OO databases
Hypertext, hypermedia and expertext
AI and expert systems
Neural networks and parallel programming
Decision support and office automation systems
CIM/CAD/CAD system
19



JAVA Features:









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

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Compiled and Interpreted
Platform-independent and portable
Object Oriented
Robust and secure
Distributed
Simple, small and familiar
Multithreaded and interactive
High performance
Dynamic and extensible
Ease of development
Scalability and performance
Monitoring and manageability
Desktop client
20

OVERVIEW OF JAVA LANGUAGE


Java is a general-purpose, object-oriented
programming language. There are two types of java
programs:
Stand-alone applications
 Web applets


Stand-alone applications are program written in
Java to carry out certain tasks on a stand-alone
local computer. Java can be used to develop
programs for all kinds of applications, which earlier,
were developed using languages like C and C++
 Applets are small Java program developed


21

Constants, Variables and Data Types
 Constants are fixed values that do not change
during the execution of the program. Java support
s several types of constants as shown in the figure
below:


22

JAVA Constants

Numeric Constants

Integer
Constants

Real
Constants

JAVA Constants

Character Constants

Character
Constants

String
Constants

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Integer Constants: refer to a sequence of digits. There exist
decimal integer, octal integer and hexadecimal integer.
 Real Constants : Integer numbers are inadequate to
represent quantities that vary continuously such as distance,
heights, temperature, prices, etc. These quantities are
represented by numbers containing fractional parts like
17.548. Such numbers are called real (or floating point)
constant. 0.0083 -0.75 435.36
 Single Character constant: A single character constant
contains a single character enclosed within a pair of single
quote marks. „5‟ „X‟ „;‟ „ „
 String Constant: A string constant is a sequence of
characters enclosed between double quotes. “Hello Java”
“1997” “Well done”


24



Variables: A variable is an identifier that denotes
a storage location to store a data value. Contrary to
the constants, a variable may take different values
at different times during the execution of the
program. A variable name can be chosen by the
programmer in a meaningful way so as to reflect
what it represents in the program. Eg. : average,
height


Variables are subjected to following conditions:
They must not begin with a digit
 Uppercase and lowercase are distinct. The variable Total is not
the same as total or TOTAL
 It should not be a keyword
 White space is not allowed
 Variable name can be of any length


25



Data Types: Every variable in Java has a data
type. Data types specify the size and type of values
that can be stores. There are various categories of
data types in Java as shown in the following figure:

26

DATA TYPES IN JAVA

Primitive (intrinsic)

Numeric

Integer

Non Primitive (Derived)

Non Numeric

Floating
point

Character

Boolean

Arrays

Classe
s

Interface

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

Integer Types: Integer types can hold whole numbers
such as 1323, -96 and 5643. The size of the values that
can be stored depends on the integer data type we
choose. There exist :
Byte = 1 byte
 Short = 2 bytes
 Int = 4 bytes
 Long = 8 bytes




Floating Point Types: Floating point type is used to
hold numbers containing fractional parts such 20.56 and
-1.76. We have:
Float = 4 bytes
 Double = 8 bytes


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Character Type: Java provides a data type called char
of a size of 2 bytes but it can hold only a single
character.
 Boolean Type: It is used when we want to test a
particular condition during the execution
of the
program. It can take two values: true or false.
 Declaration of variables: Variables should be declared
to the compiler. Declaration does three things:


It tells the compiler what the variable name is
 It specifies what type of data the variable will hold
 The place of declaration decides the scope of the variable


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

Some valid declaration are:
Int count;
 Float x,y;
 Double pi;
 Byte b;
 Char c1,c2,c3;




Giving values to variables: A variable must be
given a value after it has been declared but before
it is used in an expression. This is done in two
ways:
By using an assignment statement
 By using a read statement


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Assignment Statement:
 variableName = value


Initialvalue = 0;
 finalvalue = 100;
 Yes = „x‟;


It is also possible to assign a value to a variable at the
time of its declaration:
 type variableName = value


int finalValue = 100;
 Double total = 75.36;


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Using a read statement: values can be given to variables
through keyboard using the readLine() method as
illustrated below:
Import java.io.DataInputStream;
Class Reading
{
public static void main(String args[ ])
DataInputStream in= new DataInputStream(System.In);
int intNumber = 0;
float floatNumber = 0.0f;
Try
{
System.out.println(“Enter an Integre: “;


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intNumber = Integer.parseInt(in.readLine());
System.out.println(“Enter a float number: “);
floatNumber= Float.Value0f(in.readLine()).floatValue();
}
Catch (Exception e) { }
System.out.println(“ intNumber=“ + intNumber);
System.out.println(“floatNumber =“ + flaotNumber);
}
}

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

Scope of variables: variables are classified into
Instance variables
 Class variables and
 Local variables


34

OPERATORS AND EXPRESSIONS
Operators
 An operator is a symbol that tells the computer to
perform
certain
mathematical
or
logical
manipulations. Java operators can be classified into
a number of related categories as below:




1.Arithmetic operators:

35

Operators

Meaning

+
*
/
%

Addition or unary plus

Substraction or unary minus

Multiplication

Division

Module division

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

2.Relational operators:

Operators

Meaning

<
<=
>
>=
==
!=

Is less than
Is less than or equal
Is greater than
Is greater than or equal to
Is equal to
Is not equal to

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

3.Logical operators:

Operators

Meaning

&&

Logical AND

II

Logical OR

!

Logical NOT
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4.Assignment Operators: Assignment operators are
used to assign the value of an expression to a variable.
The operator is “=“
 5. Increment and decrement operators: The operator is
++ and –
 The operator ++ adds 1 to the operand while - - substracts
1
 6. Conditional Operator: ? is the ternary operator
available in Java, it is used to construct conditional
expression of the form exp1?exp2:exp3


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

7. Dot operator: (.) is used to access the entrance
variables and methods of class objects

Precedence of arithmetic operators
 A arithmetic expression without any parentheses will
be evaluated from left to right using the rules of
precedence of operators. There are two distinct
priority levels of arithmetic operators in java:


High priority: * / %
 Low priority: +


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Java Statements
 The statements in java are like sentences in natural
languages
 A statement is an executable combination of
variables, operators, constants ending with semi
colon (;)


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Statement
Empty Statement

Description
These do nothing and are used during program
development as a place holder

Labeled Statement

Any statement may begin with label. Labels in java
are used as the argument of jump statements

Expression Statement
Selection Statement

Combination of operators, constant of variables
These select one of several control flows. There 3
types of selection statement in Java: if, if-else; and
switch

Iteration Statement

They specify how and when looping will take place.
There are 3 types: while, do and for

Jump Statement

Jump statements pass control to the beginning or
end of the current block, or to a labeled statement.
The types are: break, continue, throw and return

Synchronization statement

These are used to handle issues with multithreading

Guarding statement

Guarding statements are used for safe handling of
code that may cause exception. The statement use
keywords: try, catch, finally

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CLASS, OBJECT, METHOD DECLARATION


Classes, Objects and Methods:
Classes provide a convenient method for packing
together a group of logical data items and function that
work on them. In Java data items are called fields and
Functions are called Methods.
 Defining a class: the basic form of class declaration is:
 Class<classname>[extends<superclassname>]
{
[variable declaration;]
[methods declaration;]
}


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 Adding variables:


Data is encapsulated in a class by placing data fields
inside the body of the class definition. These variables
are called instance variables because they are created
whenever an object of the class is instantiated. We can
create instance variable as follows:
 Class Rectangle
{
Int length;
Int width;
}


44




Adding Methods:
Methods are declared inside the body of the class but
immediately after the declaration of instance variables. The
general form of method declaration is:
 Type methodname (parameter –list)
{
Method body;
}
 Eg: void getdata (int x, int y)
{
length= x;
width= y;
}


45




Creating Objects:
Object in Java is essentially a block of memory that contains
space to store all instance variables. Creating an object is
also referred as instantiating an object. Here is an a example
of creating an object of type of rectangle.:
 Rectangle rect1= new Rectangle();
 The new operator creates an object of the specified class and
returns a reference to that object.




Arrays:


An array is a group of contiguous or related data items that
share a common name. For instance, we can define an array
name salary to represent a set of salaries of group of
employees
46

ARRAYS


Arrays:
A particular value is indicated by writing a number called
index number or subscript in brackets after the array
name. For example salary[10] represents the salary of
10th employee. While the complex set of value is
referred to as an array, the individual values are called
elements. Arrays can be any variable type:
 One dimensional array: a list of items can be given one
variable name using only one subscript and such
variable is called a single subscripted variable or a one
dimensional array.
 For instance if we want to represent a set of five
numbers, say (35,40,20,27,19) by an array variable
number, then we can create the variable number as
follows:


47

ARRAYS


Arrays:
Int number[ ]= new int[5]
The values to the array elements can be assigned as
follows:
Number [0]=35;
Number[1]=40;
Number[2]=20;
Number[3]=27;
Number[4]=19;
 Creating an array:
 Creation of an array involves three steps: (1)declare an
array, (2)create memory location, (3) put values into
memory locations


48

ARRAYS


Arrays:










(1)Declaration of array: Arrays in Java may be declared
in two forms:
Form1: type arrayname[ ];
Form2: type[ ] arrayname;
Eg: int number[ ];
float average[ ];
int[ ] number;
float[ ] average;
(2) Creating memory locations: after declaring the array,
we need to create it in the memory as shown below:
Arrayname= new type[size];
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ARRAYS


Arrays:








Eg : number= new int[5];
avergae=new float[10];
It is also possible to combine the two steps declaration
and creation into one as shown below:
Int number[ ]= new int[5];
(3)Putting values into memory locations: the final step is
to put values into the array created. This process is
known as initialization. This is done as shown below:
arrayname[subscript]=value;
Eg: number[0]=35;
number[1]=40;
number[4]=19;
50

ARRAYS


Arrays:
It is also possible to initialize arrays automatically in the
same way as the ordinary variables when they are
declared as follows:
 Type arrayname [ ]={list of values};
 Eg : int number[ ]={35,40,20,27,19};




Array length:




In Java, all arrays store the allocated size in a variable
named length. We can access the length of the array „a‟
using a.length
Eg. Int a size=a.length

51

ARRAYS


Strings:
Strings represent a sequence of characters, they may
be declared and created as follows:
String stringname;
stringname = new String(“ string”);
 Eg. String firstName;
firstName= new String(“John”)
 These 2 statements can be combined into one as
follows:
 String firstName=new String (“John”)
 Like arrays, it is also possible to get the length of string
using the „length‟ method of the string class.
int m= firstName.Length;


52

ARRAYS


Strings:
String Arrays:
 String itemArray[ ]= new String[3];
The above statement will create an array itemarray of size 3 to
hold the 3 string constants
 Multidimensional Arrays
 The array variables can store a list of values, but there will be
a situation where a table of values will have to be stored. For
that, two dimensional array can be created and used. For
creating two dimensional arrays, we must flow the same steps
as that of simple arrays.
 Eg. Int a[ ] [ ];
a=new int[3][4]; or
int a[ ] [ ]= new int[3][4];
 Theabove array declaration creates a table that can store 12
integer values, four across and three down.


53

ARRAYS


Strings:
Multidimensional Arrays
 Like one dimensional arrays, two dimensional arrays
may be initialized by following their declarations with a
list of initial values enclosed in braces.
 Eg. Int a[2][3]={0,0,0,1,1,1}; or
int a[ ][ ]= {{0,0,0},{1,1,1}};


54

RUNNING PROGRAMS
First Program:
class sample
{
public static void main (String[ ] args)
{
System.out.println("Welcome to JAVA Programming");
}
}
 Class declaration: the first line, class sample, declares a
class. Java is a true OO language, therefore, everything
must be placed into a class. Class is a key word and
declares that a new class definition follows.


55

RUNNING PROGRAMS
Opening brace: every class definition in Java logins with a
brace { and ends with a matching closing brace}
 The main line: the 3rd line, public static void main(String args[
]) defines a method named main. This is the starting point of
the interpreter to login execution of the program. A java
application can have any number of classes but only one of
them must include a main method to initiate the execution.
 Public: the key word public is access specifier that declares
the main method as unprotected and therefore it can be
accessible to all other classes
 Static: this declares the model as one that belongs to the
entire class and not the class. The main menu must always
be declared as static since the interpreter uses this method
before any objects are created


56

RUNNING PROGRAMS
Void: the type modifier void states that the main method
does not return any value. All parameters to a method
are declared inside a prior of parenthesis. Here String
args[ ] declares a parameter named args which contains
an array of objects of the class type string.
 The output line: the only executable statement in the
program is System.out.println(“Welcome to JAVA
Programming”). The println method is a member of out
objet, which is a static data member of System class.
The methods println always appends a new line
character to the end of the string, this is means that any
subsequent output will start on new line. Note the semicolon at the end of the statement. Every statement in
Java ends with a semi-colon.


57

RUNNING PROGRAMS


1.calculating the square root of a number
import java.lang.Math;
class SquareRoot
{
public static void main(String args[ ])
{
double x=5;
double y;
y=Math.sqrt(x);
System.out.println(“y=“+y);
}
}

58

RUNNING PROGRAMS
2.Displaying numbers as a triangle
class displaying
{
public static void main(String[ ] args)
{
System.out.println("Screen Display");
for(int i=1;i<=9;i++)
{
for(int j=1;j<=i;j++)
{
System.out.print(" ");
System.out.print(i);
}
System.out.print("n");
}
System.out.println("Screen Display Done");
}
}


59

RUNNING PROGRAMS


3.Area of a rectangle
class Rectangle
{
int length, width;
void getdata(int x,int y)
{
length=x;
width=y;
}
int rectArea()
{
int area=length*width;
return area;
}
}
class rectArea
{

60

RUNNING PROGRAMS
public static void main (String args[])
{
int area1, area2;
Rectangle rect1=new Rectangle();
Rectangle rect2=new Rectangle();
rect1.getdata(15,10);
area1=rect1.rectArea();
rect2.length=3;
rect2.width=5;
area2=rect2.length*rect2.width;
System.out.println("Area1="+area1);
System.out.println("Area2="+area2);
}
}

61

RUNNING PROGRAMS


4.Displaying marks
class MarkList
{ int studNo;
float Mark1,Mark2,Mark3;
char grade;
float total, average;
MarkList(int SNo,float M1,float M2,float M3)
{
studNo=SNo;
Mark1=M1;
Mark2=M2;
Mark3=M3;
}
void calculate()
{
total=Mark1+Mark2+Mark3;
average=total/3;
if((average>=90)&&(average<=100))
grade='A';
else if ((average>=70)&&(average<=89))

62

RUNNING PROGRAMS
grade='B';
else if((average>=50)&&(average<=69))
grade='C';
else
grade='D';
}
void display()
{
System.out.println("Student number="+studNo);
System.out.println("Subject1 mark="+Mark1);
System.out.println("subject2 mark="+Mark2);
System.out.println("subject3 mark="+Mark3);
System.out.println("Student Total="+total);
System.out.println("Student Average="+average);
System.out.println("Student Grade="+grade);
}
}
63

RUNNING PROGRAMS
class StudentMark
{
public static void main(String args[])
{
MarkList stud1=new MarkList(001,80,90,95);
stud1.calculate();
stud1.display();
MarkList stud2=new MarkList(002,70,50,40);
stud2.calculate();
stud2.display();
}
}
64

RUNNING PROGRAMS


5.Greatest of 3 numbers
class FindGreatest
{
Public static void main(String args[ ])
{
Int a,b,c;
a=12;
b=20;
c=10;
if(a>b)
if(a>c)
System.out.println(“ A is the Greatest”);
else
System.out.println(“C is the gretest”);
else
If(b>c)
System.out.println(“ B is the Greatest”);
else
System.out.println(“ C is the Greatest”);
}
}

65

RUNNING PROGRAMS


6. Inputs from keyboard
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
class Test
{
public static void main(String[ ] args) throws IOException
{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.print("Enter A String:");
String s = br.readLine();
System.out.print("Enter Integer:");
try
{
int i = Integer.parseInt(br.readLine());
}
catch(NumberFormatException nfe)
{
System.err.println("Invalid Format!");
}
}
}

66

EXCEPTION HANDLING


Exception: an exception is a condition that is caused
by a run-time error in the program. The purpose of the
exception handling mechanism is to provide a means
to detect and report on exceptional circumstance so
that appropriate action can be taken. The mechanism
suggests incorporation of a separate error handling
code that performs the following action:
Find the problem(Hit the exception)
 Inform that an error has occurred(Throw the exception)
 Receive the error information(Catch the exception)
 The corrective actions(Handle the exception)


67

EXCEPTION HANDLING
EXCEPTION TYPE

CAUSE OF ECXEPTION

Arithmetic Exception

Caused by math errors such as division by zero

Array index out of bounds exception

Caused by bad array indexes

Array store exception

Caused when a program tries to store the wrong
type of data in array

FileNotFound exception

Caused by an attempt to access or non existing
file

IO exception

Caused by general I/O failures, such inability to
read a file

Nullpointer exception

Caused by referencing a null object

Numberformat exception

Caused when a conversion between a string and
number fails

OutOfMemory exception

Caused when there is not enough memory to
allocate new object

Security exception

Caused when an applet tries to perform an
action not allowed by the browser‟s security
setting

StackOverflow exception

Caused when a system runs out of stack space

StringIndexOutof bounds exception

Caused when a system attempts to access a
non existing characters position in a string

68

EXCEPTION HANDLING
Java uses a keyword try to preface a block of code
that is likely to cause an error condition and “throw”
and exception
 A catch block defined by a keyword catch “catches”
the exception “thrown” by the try block and handles
it appropriately
 The catch block is immediately added after try block


69

RUNNING PROGRAMS


7. Exception handling

class Handling
{
public static void main(String args[ ] )
{
int a=10;
int b=5;
int c=5;
int x,y;
try
{
x=a/(b-c);
}
catch(ArithmeticException e)
{
System.out.println("Division by zero does not exist ");
}
}
}

70

JAVA PROGRAMMING

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