Java Type Casting

Java/J2ee Programming Training
Java Type Casting

Classification: Restricted
Agenda
• Conversion of one data type to another.
• Implicit ( lower data type to higher data type )
• Explicit ( higher data type to lower data type ) .

Implicit conversion
• Implicit
– byte b = 2;
– int i= a ;
0000000 0000000 0000000 00000010
Byte 4 Byte 3 byte2 byte1
00000010
byte1

• Explicit
– Int I = 258; (0000_0000 0000_0000 0000_0001 0000_0010 )
– byte b =(byte) I ;
0000_0000 0000_0000 0000_0001 0000_0010
0000_0010
byte1
Explicit conversion

• Explicit
– Int I = 258; (0000_0000 0000_0000 0000_0001 0000_0010 )
– byte b = (int)i;
0000_0000 0000_0000 0000_0001 0000_0010
0000_0010
byte1
Explicit conversion

• Rectangle IS- A Shape
– Rectangle has all properties of shape
• Rectangle has dim1, dim2
• Rectangle has area method
1. Rectangle rect= new Rectangle (10,20);
2. Shape s = null;
3. s = rect;
4. s.area();
1. Rectangle rect= new Rectangle ();
2. Shape s;
4. s.area()
area()
Shape
area()
Rectangle
area()
Triangle
Int d1, d2;
rect=00xx d1 = 20
d2 = 30
s= NULL
00xx
s= 00xx
JVM will invoke the method based on the type
of object reference variable is referring to @
runtime.
 “s” refers to Rectangle object at run time.
 JVM invokes area method of Rectangle class
s =rect
Typecasting—Implicit( child -> parent)

Implicit
• Triangle is a Shape
– Triangle has all properties of shape
• Triangle has dim1, dim2
• Triangle has area method
1. Triangle tri= new Triangle(20, 30 );
2. Shape s = null;
3. s = tri;
4. s.area();
1. Triangle tri= new Triangle();
2. Shape s;
4. s.area()
area()
Shape
area()
Rectangle
area()
Triangle
Int d1, d2;
tri=00xx d1 = 20
d2 = 30
s= NULL
00xx
s= 00xx
JVM will invoke the method based on the type
of object reference variable is referring to @
runtime.
 “s” refers to Triangle object at run time.
 JVM invokes area method of Triangle class
s =tri
Typecasting(reference data types)

Shape
int dim1;
Int dim2;
void area();
Rectangle
int d1 , d2;
void area(){}
1. Rectangle is a shape
i. Rect can be assigned to shape
2. Shape s;
3. Rectangle rect = new Rectangle();
4. s = rect ; shape= rectangle

Shape
1. Cuboid is a Rectangle
i. Has all properties of Rectangle
ii. Cuboid can be assigned to
Rectangle
2. Rectangle rect;
3. rect = new Cuboid();
int dim1;
Int dim2;
void area();
Rectangle
int d1 , d2;
void area(){}
Cuboid
int d1 , d2;
void area(){}
rect = cuboid
shape= rectangle

Shape
int dim1;
Int dim2;
void area();
Rectangle
int d1 , d2;
void area(){}
Cuboid
int d1 , d2;
void area(){}
Triangle
int d1 , d2;
void area(){}
rect = cuboid
shape= cuboid
rect= triangle
shape= rectangle
Cannot assign classes @
same level in hierarchy

Explicit
• Type casting base cls>child class
– Assigning reference variable of base
class to child class
– Student = User;
Login()
Logoff()
User
Login()
Logoff()
takeExam()
Student
Login()
Logoff()
evaluate()
Faculty

Explicit
• performOperation(User u )
accepts a parameter of type
User.
void performOperation(User u)
{
}
Login()
Logoff()
User
Login()
Logoff()
takeExam()
Student
Login()
Logoff()
evaluate()
Faculty
Hey Cindrela, performOperation(User u)can
accept user and its subclass( Student,
Faculty as its parameter).
yup,it can handle more than one
object….its polymorphic in nature

Hey Cindrela, performOperation(User u)can accept
user and its subclass( Student, Faculty as its
parameter).
Means.. I can pass either pass User, Student,
Faculty as a parameter….
yup,it can handle more than one object….its
polymorphic in nature
wow…That’s a gud feature in java ..
I don’t have to write a separate method for
each type of user..Ahhh gud
void performOperations( User u)
void performOperations( Student s )
void performOperations( Faculty f)
lets explore further

Explicit
: : A faculty comes @ 9:00 to
perform following operation..
{
u.login();
u.logoff();
u.takeExam();
}
Login()
Logoff()
User
Login()
Logoff()
takeExam()
Student
Login()
Logoff()
evaluate()
Faculty
Check whether the user is Faculty or User.
Let the candidate takeExam if and only if he
is a Student.

Compile Time Binding
Explicit
Login()
Logoff()
User
Login()
Logoff()
takeExam()
Student
Login()
Logoff()
evaluate()
Faculty
Faculty f = (Faculty)u
login
logoff
evaluate
login logoff
{
u.login();
u.logoff();
u.evaluate();
}
User login logoff
u.login() PASS
u.logoff PASS
u.evaluate() NO NO
{
u.login();
u.logoff();
Faculty f = ( Faculty )u;
f.evaluate();
}

Typecasting
Explicit
: : A faculty comes @ 9:00 to
{
u.login();
u.logoff();
Faculty f = (Faculty )u;
f.evaluate();
}
Login()
Logoff()
User
Login()
Logoff()
takeExam()
Student
Login()
Logoff()
evaluate()
Faculty
student..?/]
????

Explicit Conversion
Explicit
: : A student comes @ 9:05 to
{
u.login();
u.logoff();
Faculty f = (Faculty )u;
f.evaluate();
}
Login()
Logoff()
User
Login()
Logoff()
takeExam()
Student
Login()
Logoff()
evaluate()
Faculty
JOHN:I am receiving classCastException error
MIKE: perform operation method has received an
object of type student
your user is of type Student
but u are trying to cast it to FACULTY.
JOHN:How do I debug the error.
MIKE: Uas u hav passed the object of type student… cast user to
Student.
Student s = ( Student )user;

Hey Charles,We are passing Student and Faculty to
perfromOperation(User u) method… How did I
check whether user is an object of type Student or
Faculty so that I can invoke takeExam() for Student
and evaluate() for Faculty
Hey cindrella, u can use instance of operator to
find out whether the object is type of Student
or Faculty then typecast it accordingly.
Thanks Charles, Can u please show the
snippet for the same.
if ( user instanceof Student )
{
Student s = ( Student ) u;
}
else if ( user instanceof Faculty)
{
Faculty f= (Faculty ) u
}
Wow, that’s great. Let me try.!!!!

instanceof operator
Explicit
{
u.login();
u.logoff();
if( u instanceof Student )
{
Student s = ( Student ) u;
s.takeExam()
}
else if( u instanceof Faculty )
{
Faculty f = (Faculty ) f;
f.evaluate();
}
}
Login()
Logoff()
User
Login()
Logoff()
takeExam()
Student
Login()
Logoff()
evaluate()
Faculty

Classification: Restricted
Thank You

Java Type Casting

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