History
of Java
Java is the higher
level computer programming language developed by Sun Microsystems in 1991. It
is a general purpose object oriented language initially called “Oak” by James
Gosling one of the team members of inventors of the language and later in 2005
it was renamed as “Java”. Java was designed to develop software for home
appliances like TVs, VCRs, Toasters and other consumer electronic devices.
1996:
Java Development Kit 1.0 (JDK 1.0) was released by Sun Microsystems. With JDK
1.0 Java was established as internet programming language as well as general
purpose objects oriented programming language.
1997:
Java Development Kit 1.1 (JDK 1.1) was released by Sun Microsystems.
1998:
Java
2 and Software Development Kit 1.2
(SDK 1.2) was released by Sun Microsystems.
1999:
Java 2 Standard Edition (J2SE) and Java 2 Enterprise Edition (J2EE) ) was
released by Sun Microsystems.
2000:
J2SE with SDK 1.3 was released.
2002:
J2SE with SDK 1.4 was released.
2004:
J2SE with JDK 5.0 (Instead of JDK 1.5) was released with name J2SE5.0.
2006:
JDK 6 was released.
Features of Java
Compiled
and Interpreted: Generally computer programming languages uses either compiler or interpreter to convert higher level program source
code in to machine language. But java uses both, in first step java compiler
converts source code into bytecode
which is not executable. In second step java interpreter generates machine code
which is directly executable.
Portable:
Java is platform independent language; it supports various platforms like
Windows, Macintosh and various flavors of Linux and UNIX. Upgrade in Hardware
or operating system will not require any change or modification in java
program. Java ensures portability in two ways; first bytecode generated by java
complier can be implemented on nay machine. Second the size of java primitive
data types are machine independent.
Object
Oriented: Object oriented design is a programming technique
that focus on the data (objects) and interfaces to that data (object). Almost
everything in java is an object. In java all data, program code resides in the
classes and objects. Java comes with set of classes arranged in packages. We
can use these classes in our programs by inheritance.
Robust:
Java
is a robust language; the java programs are reliable in many ways. It has
strict compile time and run time checking for data types and errors in the
program. It can relieve all memory management related problems very well. Java
also incorporates the concept of exceptional handling which captures the errors
and eliminates the risk of crashing the software.
Secure:
Security
is very important for the language which is used to develop programs for network
or distributed environment like internet. Java enables development of virus
free and tamper free software. Java system also verifies memory access and
ensures virus free communication. Java doesn’t support pointers which ensure
that programs can’t access memory locations without proper authorization.
Distributed:
Java is designed as distributed language to support development of application
on internet. Java has ability to share both program and data. Java applications
can access remote objects using internet just like they can access on local
machine. This allows many programmers to work on many projects on remote
locations and work together on a single project.
Simple:
Java is a cleaned up version of C++ which can be programmed easily without any
special training. Many features of C++ which are redundant or source of
unreliable code are not available in java. For example java does not support
pointers, preprocessors header files, structures, unions, operator overloading,
multiple inheritance and many others. Java is designed similar to the C and C++
which makes it familiar to the existing C and C++ programmers. Java uses many
constructs of C and C++ therefore Java code looks like C++ code.
Multithreaded:
Multithreaded means handling multiple tasks simultaneously. Java supports
multithreading. This means the execution of a new task of an application need
not to wait to finishing of already executing task. A new task of an
application can be started even if many other tasks of that application are
already running. For example we can listen music while writing something in
word document and downloading something from a web site.
High
Performance: Performance of java is impressive due
to the intermediate bytecode. The
performance of java is high as compared to the performance of C or C++. Byte
code can be converted on the fly (at runtime) into machine code for the
particular CPU on which program is running. Java architecture is also designed
to reduce overhead at runtime. Multithreading feature of java also enhances the
overall execution speed of the java application.
Dynamic
and Extensible: Java is more dynamic as compared to C
or C++ in many ways. Java is capable of dynamically linking in new class
libraries, methods and objects. Libraries can freely add new methods and
instance variables without affecting their clients. This is an important
feature of java in the situation in which code needs to be added in the running
program.
A Java program supports
the functions written in other languages like C o C++. These functions are
known as native methods. This feature of java allows programmers to use efficient
functions available in other languages like C and C++.
Ease
of Development: Java 2 Standard Edition (J2SE) 5.0
supports various features like Generics, Enhanced for loop, Autoboxing or
unboxing, Typesafe enums, Varargs, Static import and Annotations. This feature
reduces the work of the programmer by shifting the responsibility of creating
reusable code to the java compiler. The
code created by compiler is almost bugs free because compiler makes fewer
mistakes as compared to the programmer.
Scalability
and Performance: J2SE 5.0 assures the significant
increase in scalability and performance of the java program. It improved the
startup time and reduced the amount of memory used in Java 2 runtime
environment. For example data sharing in the Hotspot Java Virtual Machine (JVM)
improves the startup time by loading the core classes from the jar file into
the shared archive. Memory utilization is reduced by sharing data in the shared
archive among multiple JVM processes.
Monitoring
and Manageability: Java supports various monitoring and
manageable APIs such as JVM Monitoring and Management API to track the
information at application level and JVM level when deploying a large
application, Sun Management Platform Extension, Logging, Monitoring and
Management Interfaces, and Java Management Extension (JMX) to Monitor and
manage java applications. Java provides tools such as Jconsole is used to
monitor JVM, Jps, Jstat and Jstatd to make use of monitoring and management
facilities.
Desktop
Client: J2SE 5.0 Provides enhanced features to meet the
challenges and requirement of the java desktop users. This feature is mainly
used for development of graphical applications that requires OpenGL hardware
acceleration.
Miscellaneous Features
Core
XML Support: J2SE 5.0 provides various powerful XML
support features to the java platform. Java has some special packages for
interface, to instantiate Simple API for XML (SAX) and Document Object Model
(DOM) parsers to parse XML document. Transform the content of an XML document,
and validate the XML document against the schema.
Supplementary
Character Support: Java adds 32 bit supplementary character
support as a part of Unicode 4.0 support. The supplementary character are
encoded with UTF-16 values to generate a different character called surrogate codepoint.
JDBC
RowSet: Java supports JDBC RowSet to send data in tabular
form between the remote components of distributed enterprise application. RowSet
contains CachedRowSet object which is a JavaBean component and acts like a
container. This object contains the number of rows of the data which are
retrieved from the database. The data stored in CachedRowSet can be directly accessed
from it without connecting to the database. JDBC RowSet also contains WebRowSet
objects which can operate without connecting to the data base or any other data
source. WebRowSet uses XML format to read and write the RowSet.
Fundamentals of Object Oriented
Programming in Java
The main objective of
object oriented approach is to eliminate some weaknesses present in the
procedural approach. Data is considered as critical part of the program in OOP.
Data is closely tied with methods which operate on that data, that way data is
protected from unintentional modification by other functions. Means data can be
modified only using the methods associated with the data. The combination of
data and methods which operates on the data makes an object.
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Data
|
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Methods
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Object = Data + Methods
Data in object oriented
programming is hidden and can’t be accessed by external functions. Objects can
communicate with each other using methods only.
Objects and Classes
Objects are the most important part of object
oriented programming. We can see many examples of real world objects around us:
our dogs, our car, our television etc.
Basically there are two characteristics of real
world objects: State and Behavior. Car has state (brand, color, current speed)
and behavior (changing gear, applying breaks). The characteristics of software
objects are also similar to real world objects.
A class can be considered as a blueprint or template
of an object. Object is an instance of the class. We can create many objects
(instances) of a class. Example of a Class
___________________________________________________________________________
public class Car {
String
brand;
String
color;
int current_speed;
void changing_gear(){
}
void applying_breaks(){
}
}
___________________________________________________________________________________
In
this example Car is a class which has data or stat (String brand; String color; int current_speed) and methods or
behavior (void changing_gear() and void applying_breaks()).
Class Car is a type; we
can now take object of this class just like we take variables of type int or
string. Example of object of class Car
Car myCar = new Car();
Car yourCar = new Car();
Here
myCar and
yourCar are the objects (instances) of class
type Car.
Encapsulation
and Data Abstraction
Encapsulation is one of
the three fundamental principles of OOP. Other two are inheritance and
polymorphism.
As we have seen above
data and methods are wrapped together in a single unit (class) is known as encapsulation.
The data encapsulated in a class is not accessible to outside functions. The
methods which are wrapped in the same class can only access the data of that
class. The methods of a class provide interface between data of the object and
program. The data of a class is invisible to the outside world so it is also
called as data hiding.
Abstraction
means representing essential features of an object without including the
background details of the object. Class uses the concept of abstraction and
includes the list of abstract attribute such as brand, color, name etc and
methods operates on these abstracts.
Inheritance
Inheritance is the
process in which an object of a class adopts properties of object of another class.
It supports the concept of hierarchical classifications. For example sports car,
sedan, suv all shares the characteristics of Car (brand, color, current speed).
Each type is a car but they have additional feature also like sports car has
only two seats, sedan has special design and 5 seats etc.
OOP allow classes to inherit commonly used properties (state
and behavior) from another class. In this example Car has become sports car,
sedan and suv. In java each class can have direct one superclass. Each super
class can support unlimited number of subclasses.
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Inheritance provides
the concept of reusability. It means we can add new features to a class without
modifying or changing existing features. A new class can be added from the
existing class as shown in above figure new class sedan is derived from existing
class Car. The new class sedan has combined feature of both the classes Car and
Sedan. More on inheritance…
Polymorphism
Polymorphism is the
ability of OOP to take more than one form. Polymorphism is the capability of
the method of a class to do different things based on the object on which it is
acting. Polymorphism allows us to define one method and have various
implementations of the method. For example: a method addition as shown in
diagram below. For two integer values passes as parameters, the method Addition will return sum (Addition) of
two values and for string values passed as parameters, the method Addition will return concatenation of
two strings. It means there are two methods of same name Addition, having different type of parameters and return values. It
is just like a word having different meaning depending of context.
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More on
polymorphism…
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