When we define any method in a class,we basically tells that this method exist and inside it it tells what
it will do.To invoke a method we will use this following statement in void main() static method
printmessage();
Now we will understand,how we can invoke this method in a program
Working:
This program has a class named as printHello and also has two methods.The first method
printmessage() used to print the message.The second method showmessage() used to call
the
first method printmessage.The calling statement printmessage() calls the method first.
Call By Value
Call by value referred to passing of a paramter to a function ,then that values of actual
parameter is
passed to formal paramters.This means When we call a method with passing argument
value to
the parameters.
These value are copied to small portion of memory and copy of this argument value is
passed to
parameters of the called method.
This argument value is used inside the called method for Read and write operation.Since
here we are
using the copied argument value,so it wont affect the original value,changes will be
there only on
that copied value
Let us understand this concept using the following example.
In this example,when show() function starts executing,it will first intialize
value of x as
10.And
it will
be stored in memory.
After that when the modify() function is triggered,the value of x as 10 gets
copied to the formal
parameters named as data.And it will also be stored in that small
heap of memory.
When the statement inside function modify() is processed,only the value of
formal parameters data
changes to 20.It wont affect actual parameter value ,as we are using
copy of that actual value.
When this function show() will get executed,you will see the
following output as:
Call by Reference
In call by reference,reference denotes memory location of
variable
Call by reference referred to passing of a parameter to a function as
a reference.This means when we call a
method by passing reference argument as a parameter.Then we are
sending both arguments as actual and formal
paramters.Both the parameters represent the same memory location
That means,the called function works on original data rather
than copied data of actual parameter.Any
changes made in that particular function,will be reflected in
the actual parameter when the function is
called.
Let us understand this concept using the following example.
In this example when display() function starts
executing,it will first create a reference variable as
ch and also D as a object.And new
reference variable created as ch will refer to
new
object D.
After that when modify() function is
triggered,new reference variable will be created and
it will
point to the same object D.That object reference
variable will be passed to formal parameter
ob.
When the statement inside modify() is
executed,any changes made in the value of
formal
parameters get reflected in the value of
actual parameter.
When this function display() will get
executed,you will see the following output.
