1. Encapsulation 2. Polymarphism 3. Inheritance
Encapsulation : Encapsulation is the concept of binding data along with its
corresponding functionalities.
Encapsulation
came into existence in order to provide
security for the data present inside
the program. Ex : Class.
Ø Encapsulation
is the back bone of OOP languages.
Ø Java
supports all the OOP concepts. (I.e. Encapsulation, Polymorphism, inheritance)
and hence it is known as Object Oriented Programming language.
Ø C++
breaks the concept of Encapsulation because the main () method in a C++ Program
is declared outside a class hence it is not a pure OOP language in fact it is a
Poor OOP Language.
Any program contains two parts:
1. Data part
2. Logic part.
·
Out of data and logic highest priority is
given to data. But in Structured programming languages the data insecurity is
high.
·
Thus in the process of securing data in
structured programming languages ,the concept of encapsulation came into
existence.
·
In Structured programming language programs,
the global variables play a vital role.
·
But because of these global variables there
is data insecurity in the structured programming language programmers. i.e.
functions that are not related to some variables are not related to
·
Some variables will have access to those
variables and thus data may get corrupted in this way data is insecure.
·
This is what people say in general about data
insecurity but this is not the actual
reason
·
Let us assume that we have a ‘C’ program with
two hundred functions assume that it is a project now if any up gradation is
required, then the client i.e. The user of this program or s/w comes to the IT
company and asks the programmers to update it according to his requirement.
The actual
concept is as follows.
·
Now we should note that it is not guaranteed
that the programmers who developed this program will still be working with that
company. Hence this project falls into the hands of new programmers. Automatically
it takes a lot of time to study the project itself before upgrading it. It may not be surprising that the time required for writing code to
upgrade the project may be very less when compared to the time required
for studying the project .Thus maintenance
becomes a problem .
·
If the new programmer adds a new function to
the exiting code in such a way of upgrading it ,
·
There is no guarantee that it will not affect
the existing functions in the code, this is because of global variables. In this way data insecurity
is created.
·
To overcome these problem programmers
developed the concept of Encapsulation.
·
For example let us have a Structured
programming language program with Ten Global variable and twenty functions.
·
It is sure that all the twenty functions will
not use all the global variables. Three of the global variables may be used
only by two functions but in a structured programming language like ‘C’ it is
not possible to restrict the access of global variables by some limited number
of functions.
Every function will
have access to all the global variables.
·
To avoid this problem, programmers have
designed a way such that the variables and the
functions which are associated with or
operate on those variables are enclosed in a block. And that
block is called a Structure or Class. And that class is given a name,
just as a function is given a name.
·
Now the variables inside the block cannot be
called as Local variables because they are not local to only one function and
they cannot be called as global variables because they are confined to a block
and not global. Hence these variables are known as “Instance Variables”.
A Simple java Program :-
Rules and
Regulations:-
Ø The
Class name should with the Capital Letter (not mandatory) but it is a
conventional rule.
Ø Java
is Case sensitive
Ø All
key words in java are written in small letters.
Ø As a
convention anything that starts with a Capital Letter is treated as a name of a
Class in java.
Following
is a simple program that prints “hello world” message.
Ex: public class Hello {
public static void main (String [] args) {
System.out.println
("Hello world");
} }
|
In the above Program,
“hello” is the class name. We have the main method which has the only one
statement in it.Note 1:- no method or function should be written in a
program without mentioning its return data type. Even in this program main ()
is a method and it returns nothing hence the keyword void is present before it.
Void indicates that the main () method does not return anything.
·
In the above program public, static, void are
keywords main () is a method. String is a class. Println
() is a method and System is class.
Let
us save this programme as Hello.java.
·
Now we compile the programme with following
command in Command Prompt.
[ D:\> javac
Hello.java ]
·
After the execution of the command Hello.class is created.
·
In other words it is the command given to the
java compiler to convert the contents of the mentioned source into its
equivalent byte code. Now the following command is given to the JVM to execute
the .class file.
Note: - Use edit plus editor for
developing java program’s.
Key
words à blue. Predefined classes -à red
Other
part of the programme is displayed in black.
So
easily recognize the syntactical and grammatical errors.
As soon as the
programme is compiled
D:\>
javac Beginner.java
Beginner.class file will be formed
D:\> java Beginner
When the above command is
given necessary part i.e.
main() method of a .class file is converted into its executable code and
is loaded into the RAM from the hard disk and made available for CPU for
execution.
Now till y = y+1 no problem.
But when the control comes
to the statement x=x+1 it generates a compilation error because x is not a
variable declared in main. But we should note that int x=10; is declared inside
the class but presently it is not available to the CPU as it is not in the RAM.
Now by using some procedure
if we are able to transfer the contents of hard disk to the RAM then x will be
resent in the RAM and it will be available to the main and thereby to the CPU
for execution.
The procedure of loading the
contents of hard disk to the RAM dynamically at runtime is done by creating an
Object. (This is need of creating an
Object.)
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