Java Datatypes

Features
• There are total 9 Data Types
• Java is a Strongly Typed Language
• No conversion !!!
• This makes it more secure and robust
• Type Compatibility Checking

Strongly Typed
• Every variable has a type
• Every expression is a type
• All assignments are checked for type
• All parameters passing are checked for type
• No confusing conversions
• All type mismatches are error

• Types
boolean either true of false
char16 bit Unicode 1.1
byte8-bit integer (signed)
short 16-bit integer (signed)
int 32-bit integer (signed)
long64-bit integer (singed)
float32-bit floating point (IEEE 754-1985)
double 64-bit floating point (IEEE 754-1985)
String (class for manipulating strings)

Ctegories
Can be classified in four Categories:
• Integers
• Floating Point
• Characters
• Boolean
(They are simple data types not objects) !!!!

Integers
Integers : Width , Usage
• byte : 8 bit , used for stream of data from network and files
• short : 16 bit , rarely used , for 16 bit computers (oudated)
• int : 32 bit, generally used
• long : 64 bit, when integer is not sufficient
In java size does not vary on platform. Though the actual size
taken in memory depends on JVM.
All are signed integers; there are no unsigned integers in java.
Width represents the behaviour , not the amount of space in
memory

Floating Point
Floating Point :
• float : 32 bit
• double : 64 bit

Float
• Single Precision
• Uses 32 bits
• Sometimes faster
• Used when not much accuracy required

Double
• Double Precision
• Uses 64 bits
• Faster on modern processors
• Used in all mathematical calculations
• More Accurate

Characters
Characters:
• char : 16 bit
• Unicode : Contains all characters of all human languages
• No negative characters
• Range 0 to 65,536
• ASCII code is from 0 to 127 which is same for Unicode
till 127.
• ++ /--/+/- operators possible

Boolean
• boolean either true or false
• Not 0 or 1
• Output of all relational and logical operators

Data Type Default Value (for fields)
byte 0
short 0
int 0
long 0L
float 0.0f
double 0.0d
char 'u0000'
String (or any object) null
boolean false

Type Conversion
Automatic Conversion will take place if:
• Two Types are compatible
• Destination is larger than source

• By Default Any Numeric Value is treated as Integer
• By default any Decimal Value is treated as Double
• Still when we assign numeric value to Byte or Short it is
OK, but if we use any value with them … Then byte and
short are converted to int.
• In Float for assignment also f is to be used
• For Long L/l is to be used

Compatible
• Numerals (byte, short, int , long, float, double) are self
compatible but not with char and boolean.
• Char and boolean are not compatible

Casting
Casting is the temporary conversion of a variable
from its original data type to some other data type.
• With primitive data types if a cast is necessary from
a less inclusive data type to a more inclusive data
type it is done automatically if they are compatible.
int x = 5;
double a = 3.5;
double b = a * x + a / x;
double c = x / 2;
• if a cast is necessary from a more inclusive to a less
inclusive data type the class must be done explicitly
by the programmer
double a = 3.5, b = 2.7;
int y = (int) a / (int) b;
y = (int)( a / b );
y = (int) a / b; //syntax error

Type Promotion
17
double
float
long
int
short,
char
byte
Outer ring is most
inclusive data type.
Inner ring is least
inclusive.
In expressions
variables and
sub expressions
of less inclusive
data types are
automatically cast
to more inclusive.
If trying to place
expression that is
more inclusive into
variable that is less
inclusive, explicit cast
must be performed.
From MORE to LESS

Double-……..int
• If either operand is double then other operands are
converted to double
• Otherwise if either operand is float other operands are
converted to float
• Otherwise if either operand is of type long other operands
are converted to long
• Otherwise both operands are converted to int

Problem
• Byte b=50;
b=b * 2;
???????

Casting …
Int a ;
Byte b;
Flaot f;
b=(byte) a;
a = (int) f;
How does it takes place:
1.Reduced Modulo
2. Truncation

Byte b;
Int i=257;
B=(byte ) i;
System.out.println( “Value of b is” + b);

Scope
• Scope is limited to a block
• Block is
{
}

3 Types of variables:
• instance variables : Variable declared inside the class;
Any method in the class definition can access these
variables
• parameter variables Only the method where the
parameter appears can access these variables. This is how
information is passed to the object.
• local variables : Declared inside the method

public class TwoSides
{
int side1, side2 ;
public boolean testRightTriangle( int hypoteneuse )
{
int side1Squared = side1 * side1 ;
int side2Squared = side2 * side2 ;
int hypSquared = hypoteneuse * hypoteneuse ;
}
}

A variable can be declared in/as:
• In a class body as class fields. Variables declared here are
referred to as class-level variables/instance variables.
• As parameters of a method or constructor.
• In a method's body or a constructor's body.
• Within a statement block, such as inside a while or for .

X : Local variable-Block
public class MainClass
{
public static void main(String[] args)
{
for (int x = 0; x < 5; x++)
{
System.out.println(x);
}
}
}

Inner block :Access Outer
Block
{
{
for (int x = 0; x < 5; x++)
{
for (int y = 0; y < 3; y++)
{ // int x; gives an error x already declared in outer block ... Not such in
// C / C++
System.out.println(x);
System.out.println(y);
}
}
}
}

{
{
int outer = 1;
{ int inner = 2;
System.out.println("inner = " + inner);
System.out.println("outer = " + outer);
}
int inner = 3;
System.out.println("inner = " + inner);
System.out.println("outer = " + outer);
}
}

class S
{ int a=5; // instance variable
public void S1()
{ int a=7; // block variable
System.out.println(a); // prints ??
}
}
public class Scope
{ int a=2; // instance variable
public static void main(String args[])
{
S x=new S(); // object x created
x.S1();
int b=5;
System.out.println(b);
}
//System.out.println(a);
// gives an error as a is instance variable and static no object created
} o/p will be 7 7 5 , local variable is given preference over instance variable

Java Datatypes

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