JAVA Data Types and Simple Program

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JAVA Data Types and Simple Program

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Title: JAVA Data Types and Simple Program

1
JAVA Data Types and Simple Program

By
Balaji.VP
9791118054
vpbala2000_at_gmail.com

2
Simple Program

Import java.lang.math
Class squareroot
public static void main (String args)
double x 5
double y
y Math.sqrt (x)
System.out.println (The Value of Y
y)

3
Explanation of the Program

The first lie is class squareroot
It is Object Oriented Construct. Nothing but
everything must be placed inside the class.
The word class is a keyword. It is used for
create a new class.
Here squareroot is identifier.
Next is braces ( This is similar to C)
The third line is public static void main (String
args )

4
Explanation of the Program

Public
The keyword public is an access specifiers
that declares the main method as unprotected and
therefore making it accessible to all other
classes.
Static
Which declares this method as one that belongs
to the entire class and not a part of the class
any objects of the class.
The main must always declare as static since
the interpreter uses this method before any
objects are created.
Void
The type modifier void states that the main
method does not return any value.

5
Second Program

Import java.lang.
Class hall
float len
float bre
void getdata (float a, float b)
len a
bre b

6
Second Program

Class area
public static void main (string args )
float area
hall hall1 new hall ()
hall1.getdata (5,10)
area hall1.len hall1.bre
System.out.println (Area area)

7
JAVA Tokens

Most statements contain expressions, which
describe the actions carried out the data.
Smallest individual units in a program are known
as Tokens.
Reserved Keywords. (60 Keywords, false, null,
true, package etc.,)
Identifiers (alphabets, digits and underscore and
dollar sign characters.)
Literals. (Integer, Floating Point. Character,
String, Boolean)
Operators.
Separators.

8
JAVA Tokens (Separators)

Parentheses () ? Method definition and
invocation, defining precedence in expressions.
Braces ? Define a block of code for classes,
methods and local scopes.
Brackets ? Declare array types and for
dereferencing array values.
Semicolon ? Separate the statements.
Comma , ? Consecutive identifiers in a variable
declaration and chain statements (For loop and
int a,b)
Period . ? Separate package names from the
sub-packages and class, separate a variable or
method from a reference variable.

9
Constants

JAVA Constants
Numeric Constants Character Constants
Integer Cons Real Cons Char Cons String
Cons
123, 0.0085, -0.75, X, 5 Hello

10
Escapes Sequences

\b --- gt Back Space.
\f --- gt Form Feed.
\n --- gt New line.
\t --- gt Horizontal Tab.

11
Data Types

Data types are two types Primitive and Non-
Primitive.
Primitive Non- Primitive
Numeric Non-Numeric Class, Arrays, Interface.
Integer, Float Char, Boolean

12
Size

Integer
Type Size
Byte 1 (Byte)
Short 2
Int 4
Long 8
Floating Point
Float 4
Double 8

13
Declaration and Giving Values

Int a
Float a,b
Double s
Byte b
Char c1,c2,c3
Int a 10
Float x 20.36
Char c1 a

14
Reading data from Keyboard

Import java.lang.
Import java.io.DataInputStream
Class read
public static void main (String args )
DataInputStream in new DataInputStream
(System. in)
int num 0
float num1 0.0f

Try
System.out.println (Enter a number )
num Integer.parseInt (in.readLine () )
System.out.println (Enter a Next Number)
num1 Float.valueOf(in.readLine() ).floatValue
()
Catch (Exception e)

System.out.println (Num num)
System.out.println (Num1 num 1)
Output
Enter a Number
123
Enter the Next Number
123.45
Num 123, Num1 1234.45

17
Scope of the Variables

Java variables are classified in three types,
1. Instance Variables.
2. Class Variables.
3. Local Variables.
The instance and class variable are declared
inside a class. Instance variable are created
when the objects are instantiated and therefore
they are associated with the objects. They take
different value for each object.
Variables declared and used inside the methods
are called local variables.

18
Symbolic Constants

Symbolic names take the same form as variable
names. But they are written in CAPITALS to
visually distinguish them from normal variable
names.
After declaration of symbolic constants, they
should not be assigned any other value within the
program by using an assignment statement.
Like final int PEOPLE 100 we can not change
the value.
This is not done in C and C where it is defined
using the define statement. They can NOT be
declared inside a method. They should be used
only as class data members in the beginning of
the class.

19
Arithmetic and Relational Operators

1. a b 10. is equal to
2. a b 11. ! is not equal to
3. a b
4. a / b
5. a b
6. lt is less than
7. lt is less than or equal to
8. gt is greater than
9. gt is greater than or equal to

20
Logical Operators

logical AND
logical OR
! logical NOT
Ex
if (age gt 55 salary lt 1000)
if (number lt0 number gt1000)

21
Assignment Operators

a a1
a a -1
a a (n 1)
a a / (n1)
a a b
y m s not equal to y m
Ex
m 5 but y m means, y 5 but m 6
y m
y 6

22
Conditional Operator

Exp1 ? Exp2 Exp3
Ex
a 10
b 15
x (agtb) ? a b
In terms of if statement
if (agtb)
x a
else
x b

23
Bitwise Operator

These operators are used for testing the bits, or
shifting them to right to left.
It is may not ne applies to float and double.
bitwise AND
! Bitwise OR
Bitwise exclusive OR
Ones Complement
ltlt shift left
gtgt shift right

24
Special Operator

There are two special operator is there,
1. instanceof
2. selection operator (.)
Instanceof
person instanceof student
If it is true the object person belongs to the
class student otherwise it is false.
Dot Operator
Person1.age // Reference to the variable age.
Person 1.salary () // Reference to the method
salary()

25
If statement

import java.lang.
class if
public static void main (String args)
int I, count, count1, count2
float weight 45.10, 55.23, 47.25, 51.23,
54.23
float height 176.23, 174.56, 168.23,
170.89, 168. 52

count 0
count 1 0
count2 0
For (i 0 i lt4 i)
if (weighti lt 50.0 height i gt 170.0)
count1 count1 1

count count 1 //Total Persons
count2 count count1
System.out.println (Number of persons with..)
System.out.println (Weight lt50 and height gt 170
count1)
System.out.println (Others count2)

28
Else If Ladder

class ladder
public static void main (String args)
int rollNumber 111, 222, 333, 444
int marks 81, 75, 43, 58
for (int i 0 i ltrollNumber. length i)
if (marks i gt79)

System.out.println (rollNumber i Honors)
else if (marks i gt 59)
System.out.println (rollNumber i I
Division)
else if (marks i gt 49
System.out.println (rollNumber i II
Division)
else
System.out.println (rollNumber i Fail
)

30
Switch case

class guide
public static void main (String args )
char ch
System.out.println (Select your Choice)
System.out.println ( M ? Madras)
System.out.println ( B ? Bombay)
System.out.println ( C ? Calcutta)

System.out.println ( Please select any one)
try
switch (ch (char)System.in.read() )
case M
case m
System.out.println ( Madras ? Booklet 5)
break

case b
case B
System.out.println ( Bombay ? Booklet7)
break
case C
case c
System.out.println ( Calcutta ? Booklet 10)
break
default
System.out.println ( Invalid Choice)

catch (Exception e )
System.out.println (I/O Error)

34
While Loop

class while
public static void main (String args )
StringBuffer string new StringBuffer ()
char c
System.out.println (Enter a string)
try

while ( ( c (char)System.in.read() ) ! \n)
string.append (c)
Catch (Exception e)
System.out.println (Error in input)

System.out.println (You have entered)
System.out.println (string)
Output
Enter a string
I am a good boy
You have entered
I am a good boy

37
Do-while

class do
public static void main (String args )
int row, column, y
System.out.println (Multiplication Table
\n)
row 1
do
column 1

do
y row column
System.out.println ( y)
column column 1
while (column lt3)
System.out.println (\n)
row row 1

while (row lt3)
Output
1 2 3
2 4 6
3 6 9

class for
public static void main (String args )
long p
int n
double q
System.out.println ( 2 to power n n 2 to
power n)
p 1

for (n 0 nlt10 n)
if (n 0)
p 1
else
p p 2
q 1.0/ (double) p
System.out.println ( q n p)

Output
2 to power n n 2to power n
1 0 1
o.5 1 2
0.25 3 4
0.00195313 9 512

43
Class, Objects and Methods

Java Program must be encapsulated in a class that
defines the state and behavior of the basic
program components knows as Objects
In JAVA Program the data items are called fields
and the functions are called methods.
class is a user defined data type with a
template that serves to define its properties.
Once the class type has been defined, we can
create variables of that type using
declarations that are similar to the basic type
declarations.

44
Define Class

class classname extends supercalssname
variable declarations
method declarations
Adding Variables
Data is encapsulated in a class by placing data
field inside the body of the class definition.
These variables are called instance variable.
They are created whenever an object of the class
is instantiated.

45
Adding Methods

Type method name ( parameter list)
method- body
Basic idea of method declaration
The name of the method.
The type of the value the method return.
A list of parameters.
The body of the method.

46
Example

class rectangle
int length, width
void getdata (int x, int y)
length x
width y

int rectArea ()
int area length width
return (area)

48
Creating Objects

Objects in Java are created using the new
operator. The new operator created an object of
the specified class and returns a reference to
that object.
Ex
rectangle rect
rect new rectangle ()
or
rectangle rect new rectangle ()

49
Accessing Class Members

Objectname.varibale name
Objectname.methodname (parameter list)
Ex
rect.length 15
rect.width 10
Calling Methods
rect. getdata (10,15)

The first one is, to access the instance variable
using the dot operator and compute the area.
int area rect.length rect.width
The second one is, to call the method area
declared inside the class, That is
int area rect1.area()

51
Constructor

Constructor have the same name as the class name
itself. They do not specify a return type, not
even void. This is because they return the
instance of the class itself.
Ex
rectangle (int x, int y)
length x
width y

52
Method Overloading

In Java, it is possible to create methods that
have the same name, but different parameter lists
and different definitions. This is called method
overloading. It is used when objects are required
to perform similar task but using different input
parameters.

53
Example

class room
float length
float breath
room (float x, float y)
length x
breath y

room (float x)
length breath x
int area ()
return (length breath)

55
Static Members

Lt us assume that we want to define a member that
is common to all the objects and accessed without
using a particular object. That is, the member
belongs to the class as a whole rather than the
object created from the class, Such members can
be defined as follows
static int count
static int max (int x, int y)
The members that are declared static as shown
above are called static members. The static
variables and static methods are often refer to
class variable, methods.

The static variables, static methods can be
called without using the objects. They are also
available for use by other classes.
Java class libraries contain a large number of
class methods. For example, the Math class of
Java library defines many static methods to
perform math operations that can be using in any
program.
float x Math.sqrt (25.0)
The method sqrt is a class method (or static
method) defined by Math class.

57
Restrictions

The static methods are called using class names.
In fat, no objects have been created for use.
They can only call other static methods.
They can only access static data.
They can not refer to this or super in any way.

58
Inheritance

The mechanism of deriving a new class from an old
one is called inheritance. The old class is known
as the base class and super class or parent
class and the new one is called the subclass or
derived class or child class.
1.Single inheritance (Only one Super class)
2. Multiple inheritance ( Several super class)
here knows as interface.
3. Hierarchical inheritance (One super class,
many subclass)
4. Multilevel inheritance (derived from a
derived class)

59
Define Sub-Class

class subclass name extends super class
variables declaration
methods declaration

60
Example

class Room
int length
int breadth
Room ( int x, int y)
length x
breadth y

int area ()
return (length breadth)
class BedRoom extends Room
int height
BedRoom (int x, int y, int z)

super (x,y)
height z
int volume ()
return (length breadth height)

class Test
public static void main (String args )
BedRoom room new BedRoom (14,12,10)
int area1 room1.area ()
int volume1 room1.volume ()
System.out.println (Area1 area1)
System.out.println (Volume1volume1)

64
Subclass Constructor

Subclass constructor is used to construct the
instance variable of both the subclass and the
super class.
The subclass constructor used the keyword super
to invoke the constructor method of the super
class.
Super may only be used within a subclass
constructor method.
The call to super class constructor must appear
as the first statement within the subclass
constructor.
The parameters in the super call must match the
order and type of the instance variable declared
in the super class.

65
Overriding Methods.

There may be occasions when we want an object to
respond to the same method but different behavior
when that method is called. That means, we should
override the method defined in the super class.
This is possible by defining a method in the
subclass that has the same name. same argument,
and same return type as a method in the super
class.
Then. When that method is called, the method
defined in the subclass is invoked and executed
instead of the one in the super class. This is
known as overriding.

66
Example

class super
int x
super (int x)
this.x x
Void display ()

System.out.println (Super X x)
class sub extends super
int y
sub (int x, int y)
super (x)

this.y y
void display ()
System.out.println (Super x x)
System.out.println (Sub y y)
class override

public static void main (String args)
sub s1 new sub (100, 200(
s1.dispaly ()

70
Final Class

A class that can not be sub classed is called a
final class. This is achieved in Java using the
keyword final.
ex
final class Aclass
Finalizer Methods
we have seen that a constructor method is used
to initialize an object when it is declared. This
process is known as initialization. Similarly,
Java supports a concept called finalization.

Java run time is an automatic garbage collecting
system. It automatically frees up the memory
resources used by the objects. But objects may
hold the other non-objects resources such as file
descriptors or windows systems fonts.
The garbage collector can not free these
resources. In order to free these we must use the
Finalizer method. This is similar to destructor
in C.
The finalizer method is simply finalize() and can
be added to any class. Java calls that method
whenever it is about to reclaim the space for
that object.

72
Abstract Methods and Class

We have seen that by making a method final we
ensure that the method is not redefined in a
subclass. That is, the method can never be sub
classed. Java allows us to do something that is
exactly opposite to this.
That is, we can indicate that a method must
always be redefined in a subclass, thus making
overriding compulsory. This is done using the
modifier keyword abstract in the method
definition.
Ex

abstract class shape
variables
abstract void draw ()

74
Access Modifiers (Visibility Modifiers)

Public
Use public if the field is to be visible
everywhere.
Protected
use protected if the field is to visible
everywhere in the current package and also
subclass in other package.
Default
Use default if the field is to be visible
everywhere in the current package only.

private protected
Use private protected if the field is to visible
only in subclass, regardless of packages.
private
Use private if the field is not to be visible
anywhere except in its own class.

76
Interface

Java provides an alternate approach known as
interfaces to support the concept of multiple
inheritance. Java class can not be a sub class
of more than one super class, it can implement
more than one interface, there by enabling us to
create classes that build upon other classes
without the problems created by multiple
inheritance.
An interface is basically a kind of class. Like
classes, interface contain methods and variables
but with a major difference.

The difference is that interface define only
abstract methods and final fields. This means
that interface do not specify any code to
implement these methods and data fields contain
only constants.
interface interface name
variables declaration
methods declaration

78
Variables and Method declaration

static final type variable name value
Method
return type method name (parameter - list)
Interface item
static final int code 1001
static final String name Fan
void display()

79
Extending Interface

Interface can also be extended, that is an
interface can be sub interfaced from other
interface. The new sub interface will inherit all
the members of the super interface in the manner
similar to sub classes.
This is achieved using the keyword extends.
Ex
interface (name2) extends (name 1)
Body of name2

interface ItemConstants
int code 1001
String name Fan
Interface Item extends ItemConstants
void display ()

81
Implementing Interface

interface area
final static float pi 3.14F
float compute (float x, float y)
Class rectangle implements area
public float compute (float x, float y)

return (x y)
class circle implements area
public float compute (float x, float y)
return (pi x x)

class InterfaceTest
public static void main (String args)
rectangle rect new rectangle ()
circle cir new circle ()
area area
System.out.println (Area of Rectangle
area.compute (10,20))

System.out.println (Area of the Circle
area.compute (10,0))

85
Exceptions Handling

An exceptions is a condition that is caused by a
run-time error in the program.
If we want a program to continue with the
execution of the remaining code, then we should
try to catch the exception object thrown by the
error condition and then display an appropriate
message for taking corrective actions. This
task is known as Exception handling.
The purpose of exception handling mechanism is to
provide a means to detect and report an
exceptional circumstance

Find the problem (Hit the exception).
Inform that an error has occurred (Throw the
exception).
Receive the error information (Catch the
exception).
Take corrective actions (Handle the exception).

87
Common Java Exceptions

ArithmeticException
Caused by math errors such as division by zero.
ArrayIndexOutOfBoundException
Caused by bad array indexes.
ArrayStoreException
Caused when a program tries to store the wrong
type of data in an array.
FileNotFoundException
Caused by an attempt to access a nonexistent
file.

IOException
Caused by general I/O failures, such as
inability to read from the file.
NullPointerException
Caused by referencing a null object.
NumberFormatException
Caused when a conversion between strings and
number fails.
OutOfMemoryException
Caused when theres not enough memory to
allocate a new object.

89
Syntax

try
Statement that causes an exception ( Exception
object creator)
catch
Statement that handles the exception (Exception
handler)

90
Program

class error
public static void main (String args )
int a 5,10
int b 5
try
int x a2 / b a1

catch (ArithmeticException e)
System.out.println (Division by zero)
catch (ArrayIndexOutofBoundException e)
System.out.println (Array index error)

catch
System.out.println (Wrong data type)
int y a1 / a0
System.out.println (Y y)

93
Using finally statement

Java supports another statement known as finally
statement that can be used to handle an exception
that is not caught by any of the pervious catch
statements. finally block can be used to handle
any exception generated within a try block.

94
Multithreaded Programming

Multithreading is a conceptual programming
paradigm where a program is divided into two or
more subprograms, which can be implemented at the
same time in parallel.
The thread is similar to a program that has a
single flow of control.

95
Creating Threads

Threads are implemented in the form of objects
that contain a method called run().
The run() method should be invoked by an object
of the concerned thread.
This can be achieved by creating the thread and
initiating it with the help of another thread
method called start().
By creating a thread class
Define a class that extends Thread class and
override its run() method with the code required
by the thread.

By Converting a class to a thread
Define a class that implements Runnable
interface. The Runnable interface has only one
method, run(), that is to be defined in the
method with the code to be executed by the thread.

97
Declaring the Class

class Mythread extends Thread
Implementing the run () method
Public void run()

98
Starting New Thread

MyThread aThread new MyThread ()
aThread.start()
Stopping a Thread
aThread.stop ()
This statement causes the thread to move to the
dead state. A thread will also move to the dead
state automatically when it reaches the end of
its method.

99
Blocking a Thread

A thread can also be temporarily suspended or
blocked from entering into the runnable and
subsequently running state by using either of the
following thread methods
sleep () // Blocked for a specified time.
suspend () // Blocked until further orders.
wait () // Blocked until certain condition
occurs.

100
Life Cycle of a Thread

During the life time of a thread, there are many
stated it can enter,
1. Newborn state.
2. Runnable state.
3. Running state.
4. Blocked state.
5. Dead state.

101
Newborn State

Schedule it for running using start () method.
Kill it using stop () method.
Runnable State
The runnable state means that the thread is
ready for execution and is waiting for the
availability of the processor. That is, the
thread has joined the queue of threads that are
waiting for execution.
If we want a thread to relinquish control to
another thread of equal priority before its turn
comes, we can do so by using yield () method.

102
Running State

Running means that the processor had give its
time to the thread for its execution.
It had been suspended using suspend () method. A
suspended thread can be revived by using the
resume () method.
It has been made to sleep, We can put a thread to
sleep for a specified time period using the
method sleep(time)where time is milliseconds.
This means that the thread is out of the queue
during this time period. The thread re-enters the
runnable state as soon as this time period is
elapsed.

103

It has been told to wait until some event occurs.
This is done using the wait () method. The thread
can be scheduled to run again using the notify ()
method.
Blocked State
A thread is said to be blocked when it is
prevented from entering into the runnable state
and subsequently the running state. This happens
when the thread is suspended, sleeping or waiting
in order to satisfy certain requirements. A
blocked thread is considered not runnable but
not dead and therefore fully qualified to run
again.

104
Dead State

Every thread has a life cycle. A running thread
ends its life when it has completed executing its
run () method. A thread can be killed as soon as
it is born, or while it is running or even when
it is in not runnable (blocked) condition.

105
Program