Java is an object oriented and structured programming language, designed by Sun Microsystems in the year 1991. Java is a third generation programming language. It has an in built application interface which has the ability to handle the graphics and user interfaces that creates the applets or applications.

The very advantage of java is its “portability”, the programmer can write the program and compile in the same kind of environment as it is written and after that it can be run anywhere.

Java relates to both C and C++, it uses the syntax of C and the object oriented concepts from c++ and this makes Java appealing. When a source code is given as the input, the output from java compiler is the “bytecode”. Bytecode contains set of instructions which will be executed by Java Virtual machine (JVM). In a more simple way, I can say JVM interprets the bytecode and this is the reason that java can be run anywhere. Applets are the programs which are embedded in to web page and can be executed where as the applications are directly executed by JVM.

It is not always possible to compile the complete program at the same time, so java uses just-in-time compiler to compile a set of bytecodes in real time for execution and the remaining codes will just be interpreted and thus makes the execution of Java program faster. The two main building blocks of java programming are the classes and objects. Objects are the instance of class and class is a template for creating objects.

Unlike in c/c++ you need not manually allocate/de allocate dynamic memory, java itself does this and also it has garbage collection for the unused objects. Java program handles the run time errors too. Java supports multithreaded programming.

Decouple validation processes from your business object implementations

Version 1.3 of the Java platform saw the introduction of the dynamic proxy facility. Dynamic proxies offer many interesting solutions to Java developers, including a validation scheme that easily decouples validation logic from an application’s core business logic. In this article, Java developer Eric Olson shows you how dynamic proxies can keep your core application code free of validation routines and focused solely on business logic.

Validation is an essential aspect of many enterprise applications. Most business methods contain validation logic to ensure that pre-conditions are met before carrying out business logic. Code that deals with values entered through a user interface employs validation logic to ensure that the values entered by a user are valid before carrying out actions that may affect other areas of the application or other users. Validation is an especially important component of applications that employ and interact with other loosely coupled components, as well as services that may not be strict in their assertions.

As important as it is to the safety and functionality of your business applications, core application logic is often cluttered with validation routines. Validation processes are often scattered throughout method calls, making it difficult to tell the difference between validation logic and core business logic. In most cases, business objects and methods must know some details of the validation process and deal with them directly in their implementation — for example, a business object may throw a validation exception directly from the business method (either coded directly in the method, or as a result of calling some validation service). The validation exception in this case is really a byproduct of the validation process, however, and would ideally be hidden from the business object implementation.

In this article, I’ll show you a more decoupled and centralized approach to validation, using the dynamic proxy facility introduced to the Java platform with version 1.3. Working with a single example throughout the article, I’ll demonstrate the weaknesses of both tightly coupled and loosely coupled validation schemes, and then show you how dynamic

What is java? For the sake of record here is a small introduction.

A high-level programming language developed by Sun Microsystems. Java was originally called OAK, and was designed for handheld devices and set-top boxes. Oak was unsuccessful so in 1995 Sun changed the name to Java and modified the language to take advantage of the burgeoning World Wide Web.

Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors. Java source code files (files with a .java extension) are compiled into a format called bytecode (files with a .class extension), which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems, including UNIX, the Macintosh OS, and Windows. Bytecode can also be converted directly into machine language instructions by a just-in-time compiler (JIT).

Java is a general purpose programming language with a number of features that make the language well suited for use on the World Wide Web. Small Java applications are called Java applets and can be downloaded from a Web server and run on your computer by a Java-compatible Web browser, such as Netscape Navigator or Microsoft Internet Explorer.