.

• What is java

  Java is a programming language originally developed by James Gosling at Sun Microsystems (which has since merged into Oracle Corporation) and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++, but it has fewer low-level facilities than either of them. Java applications are typically compiled to bytecode (class file) that can run on any Java virtual machine (JVM) regardless of computer architecture. Java is a general-purpose, concurrent, class-based, object-oriented language that is specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "write once, run anywhere" (WORA), meaning that code that runs on one platform does not need to be recompiled to run on another. Java is as of 2012 one of the most popular programming languages in use, particularly for client-server web applications, with a reported 10 million users.[10][11] The original and reference implementation Java compilers, virtual machines, and class libraries were developed by Sun from 1991 and first released in 1995. As of May 2007, in compliance with the specifications of the Java Community Process, Sun relicensed most of its Java technologies under the GNU General Public License. Others have also developed alternative implementations of these Sun technologies, such as the GNU Compiler for Java and GNU Classpath.

• why we use java

  Java is a programming language and computing platform first released by Sun Microsystems in 1995. It is the underlying technology that powers state-of-the-art programs including utilities, games, and business applications. Java runs on more than 850 million personal computers worldwide, and on billions of devices worldwide, including mobile and TV devices.
  Why do I need Java?
  There are lots of applications and websites that won't work unless you have Java installed, and more are created every day. Java is fast, secure, and reliable. From laptops to datacenters, game consoles to scientific supercomputers, cell phones to the Internet, Java is everywhere!

• Usage

  Java technology is a high-level programming and a platform independent language. Java is designed to work in the distributed environment on the Internet. Java has a GUI features that provides you better "look and feel" over the C++ language, moreover it is easier to use than C++ and works on the concept of object-oriented programming model. Java enable us to play online games, video, audio, chat with people around the world, Banking Application, view 3D image and Shopping Cart. Java find its extensive use in the intranet applications and other e-business solutions that are the grassroots of corporate computing. Java , regarded as the most well described and planned language to develop an applications for the Web. Java is a well known technology which allows you for software designed and written only once for an "virtual machine" to run on a different computers, supports various Operating System like Windows PCs, Macintoshes, and Unix computers. On the web aspect, Java is popular on web servers, used by many of the largest interactive websites. Java is used to create standalone applications which may run on a single computer or in distributed network. It is also be used to create a small application program based on applet, which is further used for Web page. Applets make easy and possible to interact with the Web page.

IBM DB2 is a relational model database server developed by IBM. There are three DB2 products that are very similar, but not identical: DB2 for LUW (Linux, Unix, and Windows), DB2 for z/OS (mainframe), and DB2 for iSeries (formerly OS/400). The DB2 LUW product runs on multiple Linux and UNIX distributions, such as Red Hat Linux, SUSE Linux, AIX, HP/UX, and Solaris, and most Windows systems. DB2 also powers the IBM InfoSphere Warehouse edition, which is basically DB2 LUW with DPF (Database Partitioning Feature), a massive parallel share-nothing data warehousing architecture. Alongside DB2 is another RDBMS: Informix, which was acquired by IBM in 2001.

The name DB2 was first given to the Database Management System or DBMS in 1983 when IBM released DB2 on its MVS mainframe platform.[1] A similar product had been named SQL/DS on the VM platform, and even earlier, in the mid 1970s, IBM released the QBE relational database product for the VM platform with a table-oriented "Query By Example" front-end which produced a linear-syntax language that drove transactions to its relational database. Later the QMF feature of DB2 produced real SQL and brought the same "QBE" look and feel to DB2. The System 38 platform also contained a relational DBMS. System Relational, or System R, was a research prototype developed in the 1970s. DB2 has its roots back to the beginning of the 1970s when EF Codd, working for IBM, described the theory of relational databases and in June 1970 published the model for data manipulation. To apply the model Codd needed a relational database language he named Alpha. At the time IBM didn't believe in the potential of Codd's ideas, leaving the implementation to a group of programmers not under Codd's supervision, who violated several fundamentals of Codd's relational model; the result was Structured English QUEry Language or SEQUEL. When IBM released its first relational database product, they wanted to have a commercial-quality sublanguage as well, so it overhauled SEQUEL and renamed the basically new language (System Query Language) SQL to differentiate it from SEQUEL. IBM bought Metaphor Computer Systems to utilize their GUI interface and encapsulating SQL platform that had already been in use since the mid 80's. When Informix Corporation acquired Illustra and made their database engine an object-SQL DBMS by introducing their Universal Server, both Oracle and IBM followed suit by changing their database engines to be capable of object-relational extensions. In 2001, IBM bought Informix Software and in the following years incorporated Informix technology into the DB2 product suite. Today, DB2 can technically be considered to be an object-SQL DBMS.
For some years DB2, as a full-function DBMS, was exclusively available on IBM mainframes. Later IBM brought DB2 to other platforms, including OS/2, UNIX and MS Windows servers, then Linux (including Linux on zSeries) and PDAs. This process occurred through the 1990s. The inspiration for the mainframe version of DB2's architecture came in part from IBM IMS, a hierarchical database, and its dedicated database manipulation language, IBM DL/I. DB2 is also embedded in the i5/OS operating system for IBM System i (iSeries, formerly the AS/400), and versions are available for z/VSE and z/VM. An earlier version of the code that would become DB2 LUW (Linux, Unix, Windows) was part of an Extended Edition component of OS/2 called Database Manager. IBM extended the functionality of Database Manager a number of times, including the addition of distributed database functionality that allowed shared access to a database in a remote location on a LAN. Eventually IBM declared that insurmountable complexity existed in the Database Manager code, and took the difficult decision to completely rewrite the software in their Toronto Lab. The new version of Database Manager, called DB2 like its mainframe parent, ran on the OS/2 and RS/6000 platforms, was called DB2/2 and DB2/6000 respectively. Other versions of DB2, with different code bases, followed the same '/' naming convention and became DB2/400 (for the AS/400), DB2/VSE (for the DOS/VSE environment) and DB2/VM (for the VM operating system). IBM lawyers stopped this handy naming convention from being used and decided that all products needed to be called "product FOR platform" (for example, DB2 for OS/390). The next iteration of the mainframe and the server-based products were named DB2 Universal Database (or DB2 UDB), a name that had already been used for the Linux-Unix-Windows version, with the introduction of widespread confusion over which version (mainframe or server) of the DBMS was being referred to. At this point, the mainframe version of DB2 and the server version of DB2 were coded in entirely different languages (PL/S for the mainframe and C++ for the server), but shared similar functionality and used a common architecture for SQL optimization: the Starburst Optimizer. Over the years DB2 has both exploited and driven numerous hardware enhancements, particularly on IBM System z with such features as Parallel Sysplex data sharing. In fact, DB2 UDB Version 8 for z/OS now requires a 64-bit system and cannot run on earlier processors, and DB2 for z/OS maintains certain unique software differences in order to serve its sophisticated customers. Although the ultimate expression of software-hardware co-evolution is the IBM mainframe, to some extent that phenomenon occurs on other platforms as well, as IBM's software engineers collaborate with their hardware counterparts.

In the mid-1990s, IBM released a clustered DB2 implementation called DB2 Parallel Edition, which initially ran on AIX. This edition allowed scalability by providing a shared nothing architecture, in which a single large database is partitioned across multiple DB2 servers that communicate over a high-speed interconnect. This DB2 edition was eventually ported to all Linux, UNIX, and Windows (LUW) platforms and was renamed to DB2 Extended Enterprise Edition (EEE). IBM now refers to this product as the Database Partitioning Feature (DPF) and sells it as an add-on to their flagship DB2 Enterprise product.
In mid 2006, IBM announced "Viper," which is the codename for DB2 9 on both distributed platforms and z/OS. DB2 9 for z/OS was announced in early 2007. IBM claimed that the new DB2 was the first relational database to store XML "natively". Other enhancements include OLTP-related improvements for distributed platforms, business intelligence/data warehousing-related improvements for z/OS, more self-tuning and self-managing features, additional 64-bit exploitation (especially for virtual storage on z/OS), stored procedure performance enhancements for z/OS, and continued convergence of the SQL vocabularies between z/OS and distributed platforms.
In October 2007, IBM announced "Viper 2," which is the codename for DB2 9.5 on the distributed platforms. There were three key themes for the release, Simplified Management, Business Critical Reliability and Agile XML development.

In June 2009, IBM announced "Cobra" (the codename for DB2 9.7 for LUW). DB2 9.7 adds data compression for database indexes, temporary tables, and large objects. DB2 9.7 also supports native XML data in hash partitioning (database partitioning), range partitioning (table partitioning), and multi-dimensional clustering. These native XML features allows users to directly work with XML in data warehouse environments. DB2 9.7 also adds several features that make it easier for Oracle Database users to work with DB2. These include support for the most commonly used SQL syntax, PL/SQL syntax, scripting syntax, and data types from Oracle Database. DB2 9.7 also enhanced its concurrency model to exhibit behavior that is familiar to users of Oracle Database and Microsoft SQL Server. In October 2009, IBM introduced its second major release of the year when it announced DB2 pureScale. DB2 pureScale is a database cluster solution for non-mainframe platforms, suitable for Online Transaction Processing (OLTP) workloads. IBM based the design of DB2 pureScale on the Parallel Sysplex implementation of DB2 data sharing on the mainframe. DB2 pureScale provides a fault-tolerant architecture and shared-disk storage. A DB2 pureScale system can grow to 128 database servers, and provides continuous availability and automatic load balancing. In 2009, it was announced that DB2 can be an engine in MySQL. This allows users on the System i platform to natively access the DB2 under the IBM i operating system (formerly called OS/400), and for users on other platforms to access these files through the MySQL interface. On the System i and its predecessors the AS/400 and the System/38, DB2 is tightly integrated into the operating system, and comes as part of the operating system. It provides journaling, triggers and other features.

DB2 for Linux, Unix and Windows has three separate editions: IBM DB2 Express-C, Workgroup Server Edition, and Enterprise Server Edition. Each of these editions has different groups of features for different sized workloads. Applications built for lower editions of DB2 are guaranteed to work on higher editions but at a higher level of performance.
The no-charge version of DB2 is called DB2 Express-C. DB2 Express-C is in some ways similar to the open source databases such as MySQL and PostgreSQL as it is offered unsupported, free of charge for unrestricted use including use in production environments. Users needing enterprise level support and fixpacks must buy any standard DB2 Edition. DB2 Express-C, however, is based on the same code as other DB2 for Linux, Unix and Windows editions and is not open source. DB2 Express-C is also similar to the free versions of Oracle database and Microsoft SQL Server, except that DB2 Express-C has no limit on number of users or on database size. DB2 Express-C runs on 32 and 64bit Windows, Linux on x86, x64 and POWER processors, Solaris on x64 CPU and Intel machines running Mac OS X. It can be installed on machines of any size, but the database engine will use only two CPU cores and 2GB of RAM. Support is provided on a free, public Web forum. For this edition there are no fixpacks or official support from IBM.

DB2 for z/OS (the mainframe) is available in its traditional product packaging, or in the Value Unit Edition, which allows customers to instead pay a one-time charge.

DB2 for i (the former DB2/400) is the third major incarnation of DB2. It is very closely incorporated into the operating system of the IBM System i machines.
DB2 also powers IBM InfoSphere Warehouse, which offers data warehouse capabilities. InfoSphere Warehouse offers several different editions and is available for z/OS, Linux, Unix, and Windows platforms. It includes several BI features such as ETL, data mining, OLAP acceleration, and in-line analytics.

An important feature of DB2 computer programs is error handling. The SQL communications area (SQLCA) structure was once used exclusively within a DB2 program to return error information to the application program after every SQL statement was executed. The primary, but not singularly useful, error diagnostic is held in the field SQLCODE within the SQLCA block.
The SQL return code values are:

0 means successful execution.

A positive number means successful execution with one or more warnings. An example is +100, which means no rows found.

A negative number means unsuccessful with an error. An example is -911, which means a lock timeout (or deadlock) has occurred, triggering a rollback.

Later versions of DB2 added functionality and complexity to the execution of SQL. Multiple errors or warnings could be returned by the execution of an SQL statement; it may, for example, have initiated a Database Trigger and other SQL statements. Instead of the original SQLCA, error information should now be retrieved by successive executions of a GET DIAGNOSTICS statement. See SQL return codes for a more comprehensive list of common SQLCODEs.

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