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Introduction to Java
Java is a simple and yet powerful object oriented programming language and it is in many respects similar to C++. Java originated at Sun Microsystems, Inc. in 1991. It was conceived by James Gosling, Patrick Naughton, et al. at Sun Microsystems, Inc. It was developed to provide a platform-independent programming language.
Platform independent
Unlike many other programming languages including C and C++ when Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by virtual Machine (JVM) on whichever platform it is being run.
What is the Java Virtual Machine? What is its role?
Java was designed with a concept of ‘write once and run everywhere’. Java Virtual Machine plays the central role in this concept. The JVM is the environment in which Java programs execute. It is a software that is implemented on top of real hardware and operating system. When the source code (.java files) is compiled, it is translated into byte codes and then placed into (.class) files. The JVM executes these bytecodes. So Java byte codes can be thought of as the machine language of the JVM. A JVM can either interpret the bytecode one instruction at a time or the bytecode can be compiled further for the real microprocessor using what is called just-in-time compiler. The JVM must be implemented on a particular platform before compiled programs can run on that platform.
Java Features
• Since Java is an object oriented programming language it has following features:
• Reusability of Code
• Emphasis on data rather than procedure
• Data is hidden and cannot be accessed by external functions
• Objects can communicate with each other through functions
• New data and functions can be easily added
• Java has powerful features. The following are some of them:-
• Platform Independent
• Simple
• Object Oriented
• Robust
• Distributed
• Portable
• Dynamic
• Secure
• Performance
• Multithreaded
• Interpreted
• Architectural Neutral
• Object Oriented Programming is a method of implementation in which programs are organized as cooperative collection of objects, each of which represents an instance of a class, and whose classes are all members of a hierarchy of classes united via inheritance relationships.
Java is:
• Object Oriented : In java everything is an Object. Java can be easily extended since it is based on the Object model.
• Platform independent: Unlike many other programming languages including C and C++ when Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by virtual Machine (JVM) on whichever platform it is being run.
• Simple :Java is designed to be easy to learn. If you understand the basic concept of OOP java would be easy to master.
• Secure : With Java secure feature it enables to develop virus-free, tamper-free systems. Authentication techniques are based on public-key encryption.
• Architectural- neutral :Java compiler generates an architecture-neutral object file format which makes the compiled code to be executable on many processors, with the presence Java runtime system.
• Portable :being architectural neutral and having no implementation dependent aspects of the specification makes Java portable. Compiler and Java is written in ANSI C with a clean portability boundary which is a POSIX subset.
• Robust :Java makes an effort to eliminate error prone situations by emphasizing mainly on compile time error checking and runtime checking.
• Multi-threaded : With Java multi-threaded feature it is possible to write programs that can do many tasks simultaneously. This design feature allows developers to construct smoothly running interactive applications.
• Interpreted :Java byte code is translated on the fly to native machine instructions and is not stored anywhere. The development process is more rapid and analytical since the linking is an incremental and light weight process.
• High Performance: With the use of Just-In-Time compilers Java enables high performance.
• Distributed :Java is designed for the distributed environment of the internet.
• Dynamic : Java is considered to be more dynamic than C or C++ since it is designed to adapt to an evolving environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve accesses to objects on run-time.
• Object Oriented Programming is a method of implementation in which programs are organized as cooperative collection of objects, each of which represents an instance of a class, and whose classes are all members of a hierarchy of classes united via inheritance relationships.
• Java is Distributed
With extensive set of routines to handle TCP/IP protocols like HTTP and FTP java can open and access the objects across net via URLs.
• Java is Multithreaded
One of the powerful aspects of the Java language is that it allows multiple threads of execution to run concurrently within the same program A single Java program can have many different threads executing independently and continuously. Multiple Java applets can run on the browser at the same time sharing the CPU time.
• Java is Secure
Java was designed to allow secure execution of code across network. To make Java secure many of the features of C and C++ were eliminated. Java does not use Pointers. Java programs cannot access arbitrary addresses in memory.
• Garbage collection
Automatic garbage collection is another great feature of Java with which it prevents inadvertent corruption of memory. Similar to C++, Java has a new operator to allocate memory on the heap for a new object. But it does not use delete operator to free the memory as it is done in C++ to free the memory if the object is no longer needed. It is done automatically with garbage collector.
• Java Applications
Java has evolved from a simple language providing interactive dynamic content for web pages to a predominant enterprise-enabled programming language suitable for developing significant and critical applications. Today, It is used for many types of applications including Web based applications, Financial applications, Gaming applications, embedded systems, Distributed enterprise applications, mobile applications, Image processors, desktop applications and many more.
OOP Concepts
• Four principles of Object Oriented Programming are
Abstraction
Encapsulation
Inheritance
Polymorphism
• Abstraction
Abstraction denotes the essential characteristics of an object that distinguish it from all other kinds of objects and thus provide crisply defined conceptual boundaries, relative to the perspective of the viewer.
• Encapsulation
Encapsulation is the process of compartmentalizing the elements of an abstraction that constitute its structure and behavior ; encapsulation serves to separate the contractual interface of an abstraction and its implementation.
• Encapsulation
* Hides the implementation details of a class.
* Forces the user to use an interface to access data
* Makes the code more maintainable.
• Inheritance
Inheritance is the process by which one object acquires the properties of another object.
• Polymorphism
Polymorphism is the existence of the classes or methods in different forms or single name denoting different implementations.