At the beginning Java was known as "oak" but it was renamed as Java in 1995. The primary goal of this language was to provide platform independent language that might be used to create software to be embedded in a variety of consumer gadgets.
Features of Java
Java is a programmer's words.
Java is cohesive and steady.
Except for those constraints imposed by the Internet environment Java provides programmer full control.
Java is to Internet programming where C was to system programming.
Importance of Java to the Internet
Java has already established a profound effect on the Internet since it allows objects to move freely in Cyberspace. Within a network there are two types of objects that are transmitted between your Server and the non-public computer.
Dynamic lively programs
The Powerful Self-executing programs cause serious problems in the areas of Security and likelihood. But Java addresses those concerns and by doing so has opened the door to an exciting new form of program called the Applet.
Java can be used to create two types of programs
Applications: An application is a program that runs on our Computer under the operating system of this computer. It is more or less like one creating using C or C++. Java's capacity to create Applets makes it important.
Applet: An Applet is an application made to be transmitted over the Internet and executed with a Java compatible web browser. An applet is truly a very small Java program, dynamically downloaded over the network, exactly like an image. However the difference is it is an sensible program, not simply a media file. It could react to the user suggestions and dynamically change.
Features of Java Security
Every time you that you download an application you are risking a viral illness. Prior to Java, most users didn't download executable programs frequently and most users were concerned about the probability of infecting their systems with a disease. Java right answers both these concerns by giving a "firewall" between a network application as well as your computer. By using a Java-compatible Web browser, you can safely and securely download Java applets without concern with virus infections.
For programs to be dynamically downloaded to all or any the many types of systems connected to the web, some means of generating portable executable code is needed. As you will notice, the same device that helps ensure security also helps create portability. Indeed Java's solution to these two problems is both chic and useful.
Java Virtual Machine (JVM)
Beyond the vocabulary there is the Java virtual machine. The Java online machine is an important aspect of the Java technology. The online machine can be embedded within a browser or an operating-system. Once a piece of Java code is loaded onto a machine, it is confirmed. Within the launching process, a class loader is invoked and does indeed byte code verification makes sure that the code that's has been made by the compiler will not corrupt the device that it's filled on. Byte code verification takes place by the end of the compilation process to make certain that is all appropriate and correct
Java architecture offers a portable, solid, high performing environment for development. Java provides portability by compiling the byte codes for the Java Virtual Machine, which is then interpreted on each program by the run-time environment
Compilation of code
When you compile the code, the Java compiler creates machine code (called byte code) for a hypothetical machine called Java Virtual Machine (JVM). The JVM is supposed to do the byte code. The JVM is established for overcoming the problem of portability. The code is written and put together for one machine and interpreted on all machines. This machine is called Java Virtual Machine.
Java was made to be easy for the Professional programmer to learn and use effectively. If you are a experienced C++ programmer, learning Java will be even easier. Because Java inherits the C/C++ syntax and lots of the objects oriented top features of C++. Most of the confusing ideas from C++ are either overlooked of Java or implemented in a cleaner, more approachable manner
Java had not been made to be source-code appropriate for any other terminology. This allowed the Java team the flexibility to design with a blank slate. One final result of this was a clean useful, pragmatic method of objects. The object model in Java is easy and easy to extend while simple types such as integers are kept as high-performance non-objects.
The multi-platform environment of the Web places extraordinary requirements on an application, because this program must implement reliably in a number of systems. The ability to create solid programs was given a high main concern in the design of Java. Java is strictly typed vocabulary; it checks your code at compile time and run time. Java virtually eliminates the problems of memory space management and de-allocation, which is completely automatic. Within a well-written Java program, all run time mistakes can -and should -be been able by your program.
The Java web server is JavaSoft's own web Server. The Java web server is merely an integral part of a larger framework, intended to provide you not only with an internet server, but also with tools. To build customized network servers for any Internet or Intranet consumer/server system. Servlets are to an online server, how applets are to the internet browser.
Servlets provide a Java-based solution used to address the problems currently associated with doing server-side coding, including inextensible scripting alternatives, platform-specific APIs, and imperfect interfaces.
Servlets are items that conform to a specific program that may be plugged into a Java-based server. Servlets are to the server-side what applets are to the client-side - object byte codes that may be dynamically packed off the web. They change from applets in that these are faceless things (without graphics or a GUI component). They serve as platform 3rd party, dynamically loadable, pluggable helper byte code items on the server area that can be used to dynamically expand server-side efficiency.
For example, an HTTP Servlets may be used to generate active HTML content. By using Servlets to do vibrant content you get the following advantages:
They're faster and cleaner than CGI scripts
They use a typical API (the Servlets API)
They provide all the benefits of Java (operate on a number of servers without having to be rewritten)
There are numerous top features of Servlets that make them easy and appealing to use.
Easily configured using the GUI-based Admin tool
Can be filled and invoked from an area drive or remotely across the network.
Can be associated together, or chained, so that certain Servlets can call another Servlets, or several Servlets in collection.
Can be called dynamically from within HTML web pages, using server-side include tags.
Are secure - even when downloading over the network, the Servlets security model and Servlets sandbox protect one's body from unfriendly tendencies.
Advantages of the Servlet API
One of the fantastic features of the Servlet API is protocol freedom. It assumes nothing about:
The protocol being utilized to transfer on the net
How it is loaded
The server environment it will be running in
Features of Servlets:
Servlets are prolonged. Servlet are loaded only by the web server and can maintain services between demands.
Servlets are fast. Since Servlets only need to be loaded once, they feature far better performance over their CGI counterparts.
Servlets are platform unbiased.
Servlets are extensible. Java is a powerful, object-oriented program writing language, which easily can be lengthened to fit your needs
A Servlet invoker is a Servlet that invokes the "service" method on the named Servlet. When the Servlet is not filled in the server, then the invoker first lots the Servlet (either from local disk or from the network) and the then invokes the "service" method. Also like applets, local Servlets in the server can be recognized by just the class name. In other words, if the Servlet name is not definite, it is cared for as local.
A consumer can invoke Servlets in the following ways:
The client can ask for a doc that is served by the Servlet.
The customer (internet browser) can invoke the Servlet straight using a Link, once it has been mapped using the Servlet Aliases section of the admin GUI.
The Servlet can be invoked through server aspect include tags.
The Servlet can be invoked by inserting it in the Servlets/ index.
The Servlet can be invoked by it in a filtration chain.
Java Database Connectivity
What Is JDBC?
JDBC is a Java API for executing SQL claims. (As a point of interest, JDBC is a trademarked name and is not an acronym; nevertheless, JDBC is often regarded as located for Java Databases Connectivity. It involves a set of classes and interfaces written in the Java program writing language. JDBC provides a standard API for tool/databases developers and makes it possible to write data source applications utilizing a natural Java API.
Using JDBC, it is simple to send SQL claims to practically any relational data source. You can write a single program using the JDBC API, and the program will be able to send SQL assertions to the correct repository. The combinations of Java and JDBC let us a programmer write it once and run it anywhere.
What Does indeed JDBC Do?
Simply put, JDBC makes it possible to do three things:
Establish a connection with a database
Send SQL statements
Process the results.
JDBC versus ODBC and other APIs
At this aspect, Microsoft's ODBC (Start Database Connectivity) API is the fact that essentially the most widely used coding interface for being able to access relational databases. It offers the capability to connect to almost all databases on almost all platforms.
So why not just use ODBC from Java? The answer is which you can use ODBC from Java, but this is best done with the aid of JDBC in the form of the JDBC-ODBC Bridge, which we covers shortly. The question now becomes "Why do you need JDBC?" There are several answers to the question:
ODBC is not befitting immediate use from Java since it uses a C interface. Telephone calls from Java to native C code have a number of drawbacks in the security, execution, robustness, and automatic portability of applications.
A literal translation of the ODBC C API into a Java API would not be desirable. For example, Java does not have any tips, and ODBC makes copious use of these, including the notoriously error-prone universal pointer "void *". You can think of JDBC as ODBC translated into an object-oriented program that is natural for Java programmers.
ODBC is hard to learn. It mixes simple and advanced functions together, and it includes intricate options even for simple inquiries. JDBC, on the other palm, was made to keep simple things simple while allowing more advanced capacities where required.
A Java API like JDBC is needed in order to permit a "pure Java" solution. When ODBC is used, the ODBC driver manager and drivers must be physically installed on every customer machine. When the JDBC drivers is written completely in Java, however, JDBC code is automatically installable, portable, and secure on all Java programs from network computers to mainframes.
Two-tier and three-tier Models
The JDBC API supports both two-tier and three-tier models for database access.
In the two-tier model, a Java applet or request talks right to the database. This involves a JDBC drivers that can communicate with the particular repository management system being reached. A user's SQL assertions are delivered to the data source, and the results of those statements are sent back to an individual. The data source may be located on another machine to which the user is linked via a network. That is known as a consumer/server configuration, with the user's machine as your client, and the device housing the data source as the server. The network can be an Intranet, which, for example, links employees in a corporation, or it could be the web.
Java applet or
Client machine (GUI)
HTTP, RMI, or CORBA calls
Server machine (business Logic)
In the three-tier model, commands are delivered to a "middle tier" of services, which in turn send SQL assertions to the database. The database processes the SQL claims and directs the results back to the center tier, which in turn sends those to the user. MIS directors find the three-tier model very attractive because the middle tier can help you maintain control over gain access to and the sorts of updates that may be made to corporate and business data. Another edge is that whenever there's a middle tier, an individual can use an easy-to-use higher-level API which is translated by the middle tier into the appropriate low-level calls. Finally, in many cases the three-tier architecture can provide performance advantages.
Until now the center tier has typically been written in languages such as C or C++, which offer fast performance. However, with the release of optimizing compilers that convert Java byte code into effective machine-specific code, it is now practical to implement the center tier in Java. This is a huge plus, so that it is possible to have advantage of Java's robustness, multithreading, and security features. JDBC is important to permit database access from a Java middle tier.
JDBC Drivers Types
The JDBC drivers that we are aware of at this time fit into one of four categories:
JDBC-ODBC bridge plus ODBC driver
Native-API partly-Java driver
JDBC-Net pure Java driver
Native-protocol genuine Java driver
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