Class
Class is a
collection of data members and member functions.
Data members
Data
members are nothing but simply variables that we declare inside the class so it
called data member of that particular class.
Member functions
Member
functions are the function or you can say methods which we declare inside the
class so it called member function of that particular class. The most important
thing to understand about a class is that it defines a new data type. Once
defined, this new type can be used to create objects of that type. Thus, a
class is a template for an object, and an object is an instance of a class.
Because an object is an instance of a class, you will often see the two words
object and instance used interchangeably.
Syntax of class:
class
classname
{
type instance-variable1;
type instance-variable2;
//....
type instance-variableN;
type methodname1(parameter-list)
{
// body of method
}
type methodname2(parameter-list)
{
// body of method
}
// ...
type methodnameN(parameter-list)
{
// body of method
}
}
When we define a class, you declare its exact form and
nature. We do this by specifying the data that it contains and the code
that operates on that data. The data, or variables, defined within a class are
called instance variables. The code is contained within
methods.
NOTE : C++ programmers will notice that the class
declaration and the implementation of the methods are stored in the same
place and not defined separately.
Syntax:
accessing data member of the class: objectname.datamember
name;
accessing methods of the class: objectname.method name();
So for accessing data of the class: we have to use (.)
dot operator.
NOTE: we can use
or access data of any particular class without using (.) dot operator from
inside that particular class only.
How to declare object of class in java?
Syntax of object:
classname objectname; \\
declaration of object.
objectname = new classname(); \\
allocate memory to object (define object).
or we can directly define object like this
classname objectname = new classname();
Assigning Object Reference Variables :
Suppose
Box b1 = new Box();
Box b2 = b1;
Here b1 is the object of class Box. And we assign b1 to b2
by b2=b1.
Here we did not use new keyword for b2 so b1 and
b2 will both refer to the same object. The assignment of b1 to b2 did not
allocate any memory or copy any part of the original object. It simply makes b2
refer to the same object as does b1.Thus, any changes made to the object
through b2 will affect the object to which b1 is referring, since they are
the same object.
NOTE: When
you assign one object reference variable to another object reference variable,
you are not creating a copy of the object, you are only making a copy of
the reference.
Anurag
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