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Q606. What restrictions are placed on method overriding?
Ans. Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
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Ans. When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.
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Ans. RMI stands for Remote Method Invocation. Traditional approaches to executing code on other machines across a network have been confusing as well as tedious and error-prone to implement. The nicest way to think about this problem is that some object happens to live on another machine, and that you can send a message to the remote object and get a result as if the object lived on your local machine. This simplification is exactly what Java Remote Method Invocation (RMI) allows you to do.
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Ans. JMS Provides high-performance asynchronous messaging. It enables Java EE applications to communicate with non-Java systems on top of various transports.
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Ans. EJB Provides a mechanism that make easy for Java developers to use advanced features in their components, such as remote method invocation (RMI), object/ relational mapping (that is, saving Java objects to a relational database), and distributed transactions across multiple data sources.
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Ans. 1) It is an Action based MVC based framework which has adopt mvc2.
2) Struts2 is a pull-MVC (or MVC2) framework where action takes the role of the model rather than the controller. The “pull†concepts means views ability to pull data from an action, rather than having a separate model object available.
3) The Model View-Controller pattern in Struts2 is implemented with five core components – actions, interceptors, value stack / OGNL, result types and results / view technologies.
4) XML configuration as well as Annotation option available.
5) POJO based action available so we can write test cases easily.
6) Integration with Spring, tiles and OGNL based expression langugae.
7) Theme based tag libraries integrated with struts tag as well as support of Ajax tag.
8) Can have various view options like jsp, velocity, freemarker etc.
9) We can embed plugin through which we can modify and extend framework features.
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Ans. Suppose we want to visit a site for any information, information can be represented in different languages like English,German or may be other and their format for presentation can also differ from HTML to PDF or may be Plain text. In this case when an client makes an HTTP request to a server, client can also specify the media types here. Client can specify what it can accept back from host and on the basis of availability the host will return to the client. This is called content negotiation because client and server negotiated on the language and format of the content to be shared.
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Ans. A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword. Here is an example:
static {
// whatever code is needed for initialization goes here
}
A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code.
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Ans. Sometime we just need classes or class objects just to be used as part of a particular class or objects. Making them non nested won't make any difference as far as functionality is concerner but making them Nested provide a level of convenience and protection fro, being used anywhere else. Moreover it helps reducing the Code.
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Ans. Annotations, a form of metadata, provide data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate. Annotations have a number of uses, among them: • Information for the compiler — Annotations can be used by the compiler to detect errors or suppress warnings. • Compile-time and deployment-time processing — Software tools can process annotation information to generate code, XML files, and so forth. • Runtime processing — Some annotations are available to be examined at runtime.
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Q621. Difference between implicit and explicit type casting ?
Ans. An explicit conversion is where you use some syntax to tell the program to do a conversion whereas in case of implicit type casting you need not provide the data type.
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Ans. The assert keyword is used to make an assertion—a statement which the programmer believes is always true at that point in the program. This keyword is intended to aid in testing and debugging.
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