ConstVarDataTypes

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Chapter-4

Constants, Variables and Data TypesPresented by Anurag Kumar


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anuraggie- [email protected]

Constants

Java

Constant

s

Numeric

Constants

Character

Based

Constants

Integer

Constants

Real

Constants

Character

Constants

String

Constants


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Numeric ConstantsInteger Constants

oDecimal integers e.g. 12 -321 0 654

o

Octal integers e.g. 037 0435 0551 041oHexadecimal integers 0X2 0xbc4 0X79

Real Constants

oFixed-Point Notation e.g. 0.0045 -45.6 .56

oScientific Notation e.g. 4.5e-3 -4.5E1 5.6e-1


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Character Based ConstantsCharacter Constants

oe.g. P d 6 ; }

o

Escape Sequences \b \f \n \r \t \ \ \\

String Constants

oe.g. Hello World 2005 ?!


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VariablesA variable is an identifier that denotes a storage location

used to store a data value.

Unlike constants, variable may take different values atdifferent times during the execution of the program.


6/29anuraggie- [email protected]

Data TypesEvery variable in Java must have a datatype.

Data type specify the size of the variable.

Data type also specify the type of values that can bestored in the variable.



Data Types inJava

Primitive(Intrinsic

)

Non-Primitive

(Derived)

Numer

ic

Non-

Numeric

Classe

s

Arrays Interfa

ces

Integ

er

Floating-

Point

Chara

cter

Boole

an

byte

short

int

long

float

double

char boolea

n



Integer Types



Floating Point Types



Character TypeThe data type is char.

The size of char data type is 2 bytes.

the range of char is 0 to 65536. There are no negativechars.

Java uses UNICODE to represent characters.

UNICODE is a 16-bit character coding system and

supports more than 34000 characters derived from 24languages from America, Europe, Middle East, Africa

and Asia (including India).



Boolean TypeJava has a simple type, called boolean, for logical

values.

It can have only two values, true orfalse.

This is the type returned by all relational operators, such

as: a>b

boolean is also the type required by the conditional

expressions that govern the control statements such asif, while, do...while and for.



Declaring a VariableVariables are the names of storage locations.

A variable declaration 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.

A variable must be declared before its use.

e.g. int x;

float x,y,z;type identifier1, identifier2,...,identifierN;



Initializing a VariableGiving a value to a variable at the time of its declaration

is called Initialization. e.g.

int x=5;float x=4, y=3, z=5;

char c = p;

Dynamic Initialization

ovaraible can be initialized dynamically, using an

expression at the time when the variable is declared. e.g.

int a=4,b=5; //initialization

int x=a*b; //dynamic initialization



Giving values to variablesBy using an assignment statement

By using read statement

By using assignment statement

varaiableName = value


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By using Read StatementReading a Single Character

import java.io.*;

class BRRead{public static void main(String args[ ]) throws IOException {

char c;

BufferedReader br=new BufferedReader(new

InputStreamReader(System.in));c = (char) br.read();

System.out.println(c);

}

}


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By using Read StatementReading an Integer

import java.io.*;

class BRRead{public static void main(String args[ ]) throws IOException {

int n;

BufferedReader br=new BufferedReader(new

InputStreamReader(System.in));n =Integer.parseInt(br.readLine());

System.out.println(n);

}

}


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Reading other types of valuesBufferedReader br=new BufferedReader(new

InputStreamReader(System.in));

String s=in.readLine();Byte b=Byte.parseByte(in.readLine());

short s= Short.parseShort(in.readLine());

int i=Integer.parseInt(in.readLine());

long l=Long.parseLong(in.readLine());

float f=Float.parseFloat(in.readLine());

double d=Double.parseDouble(in.readLine());


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Scope of Variablesinstance variables

oare declared inside the class.

oare created when the objects are instantiated.

oare assoicated with the objects.

otake different values for different objects.

class variables

oare declared inside the class as static.

oare global to the class and belongs to entire set ofobjects that class creates.

oonly one memory location is created for each class

variable.

local variables: are declared inside the methods.


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Scope of local variables

{

int x=0;

}

{

:

int n=5;

:

}

{

:int m=10;

:

}

Block 1

Block

2

Block

3


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Symbolic ConstantsSymbolic constants are declared using a keyword final.

Symbolic names are generally written in capitals.

After declaration of symbolic constants, they should notbe assigned any other value within the program by

using an assignment operator.

Symbolic constants are declared for types. This is not

done in C where symbolic constants are declared using#define preprocessor directive.

Symbolic constants in java can not be decalred inside

the methods. They can only be declared as class data

members. e.g.

final type SYMBOLIC_NAME =

value;


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Javas Automatic Type ConversionJavas Automatic Type Conversion takes place if

othe two types are compatible.

othe destination type is larger than the source type.

(widening takes place)

NOTE:

oAll numeric types are compatible with each other.

oNumeric types are not compatible with boolean and char.

oAlso charand boolean are not compatible with each

other.


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Type Casting for casting Incompatible TypesFornarrowing conversion we need type casting.

Type casting may result in loss of information in case of

narrowing.

e.g.

int x=256;byte b=(byte) x;

(target_type) value


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Automatic Type Promotion in Expressionsin an expression the precision required of an

intermediate value will sometimes exceed the range of

either operand.

byte b = 50;

b = b * 2; // Java promotes byte and short operand to int

whenevaluating an expression

so the correct statement will be:

b = (byte)( b * 2);


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Type Promotion RulesAll byte and short values are 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, then the expression is

promoted to double


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Outputting valuesprint()

println()

ex 1:

System.out.print(Hello);

System.out.print(, World);

ex 2:

System.out.println(Hello);

System.out.println(, World);

Hello,

World

Hello

, World


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Outputting valuesclass PrintTest{

public static void main(){

int n=5;

int sq = n * n;

System.out.println(The Square of + n + is : + sq);

}

}

The Square of 5 is: 25


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Default Values of various types of Variables

byte 0

short 0

int 0

long 0

float 0.0f

double 0.0char null

boolean false

reference null


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AssignmentsQ.1 What are symbolic constants? How are they useful in

developing programs.

Q.2 List the eight basic data types available in java. Explain

them using examples.

Q.3 Explain Javas Au tomat ic Type Convers ionand Type

Casting.


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End of Chapter-4

Thank You

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