Features of java language

The massive growth of the internet and world wide web leads us to a completely new way of looking development and distribution of software. Apart from being java is system independent language, java having many other features also. Let us have a look at some of its features.

·         Simple

·         Object oriented

·         Robust

·         Secure

·         Distributed

·         Architectural neutral

·         Portable

·         Interpreted

·         High performance

·         Multithreaded

·         Scalability

·         Dynamic

Simple: Java was designed to be easy for the professional programmer to learn and use effectively. Assuming that you have some programming experience, you will not find Java hard to master. If you already understand the basic concepts of object-oriented programming, learning Java will be even easier. Best of all, if you are an experienced C++ programmer, moving to Java will require very little effort. Because Java inherits the C/C++ syntax and many of the object-oriented features of C++, most programmers have little trouble learning Java. Also, some of the more confusing concepts from C and C++ are omitted in java . for example the concept of pointers, which is very difficult for both learners and programmers, that has been eliminated in java. Beyond its similarities with C/C++, people who know c and c++ can learn java easily.

Q: why pointers are eliminated in java?

A: 1. Pointers is eliminated in java because pointers concept are complicated for the programmer. pointers are not secure.

     2. sometimes pointers may crash programs easily, for example when we add two pointers,        the     program crash immediately. And when we forgot to free the memory allotted to a variable    and reallot it to some other variable, then also program will crash.

     3. using pointers  harmful programs like virus and other hacking programs can be developed.                So pointers breaks security

Object oriented:  Java was not designed to be source-code compatible with any other language. This allowed the Java team the freedom to design with a blank slate. One outcome of this was a clean, usable, pragmatic  approach to objects. That means  java program use objects and classes. What is an object? An object is anything that really exists in the real world and can be distinguished from others. Everything that we see physically will come into this definition. For example book, tree, human being…and so on.

Every object has properties and exhibits certain behavior. For example let us assume a  cat . It got properties like name, color, height, age .. etc. these properties are represented by variables. Now the object  cat will have some actions like walking, eating, jumping  etc. these actions are represented by various methods(functions) in our programming. So we can say the objects contain variables and methods.

A group of objects exhibiting same behavior (properties and actions) will comes under the same group called class. A class represents  a group of several objects.  For example take flower:  jasmine,rose, lilly. All these are exhibit same behavior and hence they belongs to same group. So flower is the class name and having three objects. And we can say a class is a model or blueprint for creating the objects.

                               

Q: what is the difference between a method and function?

A:  a method is a function that is written in a class. We don’t have functions in java, instead we have methods. This means whenever a function is written in java, it should be written inside the class only. But if we take c++, we can write the functions inside as well as outside the class. So in c++, they are called member functions.

Since java is purely object oriented programming language , so that if we write java program we need atleast one  class or one object. C++ is not pure object oriented language so it is possible to write programs in c++ without writing class or object.

Robust: robust means strong, java programs are strong and they don’t crash easily. the ability to create robust programs was given a high priority in the design of Java. To gain reliability, Java restricts you in a few key areas, to force you to find your mistakes early in program development. At the same time, Java frees you from having to worry about many of the most common causes of programming errors. Because Java is a strictly typed language, it checks your code at compile time. However, it also checks your code at run time. To better understand how Java is robust, consider two of the main reasons for program failure: memory management mistakes and mishandled exceptional conditions (that is, run-time errors). Memory management can be a difficult, tedious task in traditional programming environments. For example, in C/C++, the programmer must manually allocate and free all dynamic memory. This sometimes leads to problems, because programmers will either forget to free memory that has been previously allocated or, worse, try to free some memory that another part of their code is still using. Java virtually eliminates these problems by managing memory allocation and deallocation . (In fact, deallocation is completely automatic, because Java provides garbage collection for unused objects.) Exceptional conditions in traditional environments often arise in situations such as division by zero or “file not found,” and they must be managed with clumsy and hard-to-read constructs. Java helps in this area by providing object-oriented exception handling.

Q: what is garbage collector and which part of jvm will allocate the memory for a program?

A: garbage collector is a form of memory management that checks the memory from time to time and marks the variables or objects not used by the program automatically. Class loader subsystem of jvm will allocate the necessary memory needed by the program.

Q: which algorithm is used by garbage collector to remove the unused variables or objects from memory?

A:  mark and sweep algorithm

Q: how can we call the garbage collector?

A: garbage collector is automatically invoked when the program is being run. It can be also called by calling gc() method of Runtime class or System class.

Secure: security problems like tampering, eavesdropping , virus threats can be eliminated by using java on internet.

-No explicit pointer

-Programs run inside virtual machine sandbox.

-Classloader: adds security by separating the package for the classes of the local file system from those that are imported from network sources.

-Bytecode Verifier: checks the code fragments for illegal code that can violate accesss right to objects.

-Security Manager: determines what resources a class can access such as reading and writing to the local disk.

Distributed: Java is designed for the distributed environment of the Internet, because it handles TCP/IP protocols. In fact, accessing a resource using a URL is not much different from accessing a file. The original version of Java (Oak) included features for intra- address-space messaging. This allowed objects on two different computers to execute procedures remotely. Java revived these interfaces in a package called Remote Method Invocation (RMI). This feature brings an unparalleled level of abstraction to client/ server programming.

Architectural neutral: java uses byte code which is not system dependent. It can run on any machine with any processor and any operating system.

Portable: if a program gives same result on every machine, then that program is called portable. Java programs are portable programs.

Interpreted:  when compile the java programs , they generates  byte code. This byte code is downloaded and interpreted by the interpreter in JVM. Interpreting means converting byte code into machine code. If we take any other languages only an interpreter or compiler is used to execute the programs. But in java, we use both compiler and interpreter for the execution.

High performance:   the problem with  interpreter inside the jvm is that it is slow. Because of this, java programs used to run slow. To overcome this problem, along with the interpreter, java people  have  introduced JIT(just in time) compiler, which enhances the speed of execution. So in jvm  ,interpreter and JIT compiler work together to run the program.

Multithreaded:   a thread represents an individual process to execute a group of statements. Java was designed to meet the real-world requirement of creating interactive, networked programs. To accomplish this, Java supports multithreaded programming, which allows you to write programs that do many things simultaneously.

Scalability: java platform can be implemented on a wide range of computers with varying levels of resources , form embedded device to mainframe computers. This is possible because java is compact and platform independent.

Dynamic: before development of java, only static text used to be displayed in the browser. Java programs carry with them substantial amounts of run-time type information that is used to verify and resolve accesses to objects at run time. This makes it possible to dynamically link code in a safe  manner. This is crucial to the robustness of the applet environment, in which small fragments of byte code may be dynamically updated on a running system.