Showing posts with label WAR. Show all posts
Showing posts with label WAR. Show all posts

January 03, 2022

Top 20 Apache Tomcat Interview Questions and Answers

  

       Tomcat is a Java Servlet container and web server developed by the Apache Software Foundation's Jakarta project. Client browsers send queries to a web server, which the server answers to with web pages. Web servers can generate dynamic content based on the user's requests. Because it supports both Java servlet and JavaServerPages (JSP) technologies, Tomcat excels at this. Even if a free servlet and JSP engine is required, Tomcat can be utilised as a web server for a variety of applications. It can run on its own or alongside standard web servers like Apache httpd, delivering static pages while Tomcat handles dynamic servlet and JSP queries.

    Apache Tomcat is an open source Java Servlet, JavaServer Pages, Java Expression Language, and Java WebSocket implementation platform. Many firms are hiring Devops engineers, Apache Tomcat administrators, Linux Apache Tomcat jobs, and Hadoop developers at varying levels of experience. The most popular Web server is Apache, and you must be familiar with it if you plan to work as a Middleware/System/Web administrator. Apache HTTP is a free and open-source web server that runs on Windows and Linux.

 Apache Kafka Interview Questions and Answers

Ques. 1): Who is in charge of Tomcat?

Answer:

The Apache Software Foundation is the correct answer. The Apache Software Foundation is a non-profit organisation that oversees several Open Source projects.

The Apache Software Foundation's Java-based projects are referred to as Jakarta.

Tomcat is an Apache Jakarta project that manages server-side Java (in the form of Servlets and JSPs). Tomcat is the "reference" implementation of the Servlet and JSP specifications, which means that anything that runs in Tomcat should run in any compliant Servlet / JSP container.

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Ques. 2): Difference between apache and apache-tomcat server?

Answer: 

Apache: Apache is mostly used to serve static content, but there are numerous add-on modules (some of which are included with Apache) that allow it to modify the content and serve dynamic content written in Perl, PHP, Python, Ruby, and other languages.

Apache is an HTTP server that serves HTTP requests.

Tomcat is a servlet/JSP container developed by Apache. It's written in the Java programming language. Although it can provide static information, its primary function is to host servlets and JSPs.

JSP files (which are comparable to PHP and older ASP files) are converted into Java code (HttpServlet), which is then compiled into.class files and run by the Java virtual machine by the server.

Apache Tomcat is used to deploy your Java Servlets and JSPs. So in your Java project, you can build your WAR (short for Web ARchive) file, and just drop it in the deploy directory in Tomcat.

Although it is possible to get Tomcat to run Perl scripts and the like, you wouldn’t use Tomcat unless most of your content was Java.

Tomcat is a Servlet and JSP Server serving Java technologies

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Ques. 3):  What exactly is Coyote?

Answer:

Coyote is a Tomcat Connector component that acts as a web server and supports the HTTP 1.1 protocol. This enables Catalina, which is ostensibly a Java Servlet or JSP container, to additionally serve local files as HTTP documents.

Coyote monitors a specific TCP port for incoming connections to the server and transmits the request to the Tomcat Engine, which processes the request and returns a response to the requesting client.

Coyote is Tomcat's HTTP connector, which offers an interface for browsers to connect to.

 Apache Hive Interview Questions & Answers

Ques. 4): What is a servlet container?

Answer:

A servlet container is a web server component that communicates with Java servlets. The servlet container is in charge of managing servlet lifecycles, mapping URLs to specific servlets, and ensuring that the URL requester has the appropriate access privileges.

Requests to servlets, JavaServer Pages (JSP) files, and other types of files containing server-side code are handled by the servlet container. The Web container generates servlet instances, loads and unloads servlets, creates and manages request and response objects, and handles other servlet-related operations.

The web component contract of the Java EE architecture is implemented by the servlet container, which defines a runtime environment for web components that includes security, concurrency, lifecycle management, transaction, deployment, and other services.

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Ques. 5): How Do I Can Change The Default Home Page Loaded By Tomcat?

Answer :

We can easily override home page via adding welcome-file-list in application $TOMCAT_HOME/webapps//WEB-INF /web.xml file or by editing in container $TOMCAT_HOME/conf/web.xml

In $TOMCAT_HOME/conf/web.xml, it may look like this:

    index.html

    index.htm

    index.jsp

Request URI refers to a directory, the default servlet looks for a "welcome file" within that directory in following order: index.html, index.htm and index.jsp

Apache NiFi Interview Questions & Answers 

Ques. 6): what is a difference between Apache and Nginx web server?

Answer:

Both are classified as Web Servers, but there are a few key differences. Nginx is an event-driven web server, whereas Apache is a process-driven web server.

Nginx has a reputation for being faster than Apache.

Whereas Nginx does not support OpenVMS or IBMi, Apache supports a wide range of operating systems.

Nginx is still catching up to Apache in terms of module interoperability with backend application servers.

Nginx is a lightweight web server that is rapidly gaining market share. If you're new to Nginx, you might be interested in reading some of my Nginx articles.

 Apache Ant Interview Questions and Answers

Ques. 7): How Do You Create Multiple Virtual Hosts?

Answer :

If you want tomcat to accept requests for different hosts e.g. www.myhostname.com then you must

Create ${catalina.home}/www/appBase , ${catalina.home}/www/deploy, and ${catalina.home}/conf/Catalina/www.myhostname.com

Add a host entry in the server.xml file

Create the the following file under conf/Catalina/www.myhostname.com/ROOT.xml

Add any parameters specific to this hosts webapp to this context file

Put your war file in ${catalina.home}/www/deploy

When tomcat starts, it finds the host entry, then looks for any context files and will start any apps with a context.

 

Ques. 8): In Apache Tomcat, what is Catalina?

Answer:

Once Jasper has completed the compilation, it turns JSP into a servlet, which Catalina can then manage. Catalina is a servlet container for Tomcat. It also implements all of the Java server page and servlet specs. Catalina is a Java engine embedded into Tomcat that provides an efficient environment for servlets to execute in.

 

Ques. 9): What exactly do you mean by Tomcat's default port, and can it be used with SSL?

Answer:

Tomcat uses port 8080 as its default port. Well, you can change it by editing the server.xml file in the Tomcat install directory's conf folder. By adjusting the property to the desired port connection port="8080" and then restarting Tomcat, the modifications will take effect.

Tomcat can use SSL, but it will require some configuration. You must complete the following tasks:

Generate a keystore

Then add a connector in server.xml

Restart Tomcat

 

Ques. 10): What is a mod_evasive module, and what does it do?

Answer:

Mod_evasive is a third-party module that accomplishes one simple task really well. It identifies when your site is under attack by a Denial of Service (DoS) attack and mitigates the harm that the attack causes. When a single client makes repeated requests in a short period of time, mod evasive recognises this and refuses additional requests from that client. The ban can last for a very short time because it is simply reissued the following time a request is discovered from that same host.

 

Ques. 11): Explain Directory Structure Of Tomcat?

Answer :

Directory structure of Tomcat are:

bin - contain startup, shutdown, and other scripts (*.sh for UNIX and *.bat for Windows systems) and some jar files also there.

conf - Server configuration files (including server.xml) and related DTDs. The most important file in here is server.xml. It is the main configuration file for the container.

lib - contains JARs those are used by container and Servlet and JSP application programming interfaces (APIs).

logs - Log and output files.

webapps – deployed web applications reside in it .

work - Temporary working directories for web applications and mostly used during in JSP compilation where JSP is converted to a Java servlet.

temp - Directory used by the JVM for temporary files .

 

Ques. 12): Explain How Running Tomcat As A Windows Service Provides Benefits?

Answer :

Running Tomcat as a windows service provides benefits like:

Automatic startup: It is crucial for environment where you may want to remotely re-start a system after maintenance

Server startup without active user login: Tomcat is run oftenly on blade servers that may not even have an active monitor attached to them. Windows services can be started without an active user

Security: Tomcat under window service enables you to run it under a special system account, which is protected from the rest of the user accounts

 

Ques. 13): How Do Servlet Life Cycles Work?

Answer:

The life-cycle of a typical Tomcat servlet is as follows:

Through one of its connectors, Tom-cat receives a request from a client.

This request will be processed. This request is routed through Tomcat to the proper server.

Tomcat checks that the servlet class has been loaded after the request has been forwarded to the proper servlet. If it isn't, Tomcat wraps the servlet in Java Bytecode, which is executed by the JVM and creates a servlet instance.

The servlet is started by Tomcat by invoking its init method. The servlet includes code that can inspect Tomcat configuration files and take appropriate action, as well as declare any resources it might need.

Once the servlet has been started, Tomcat can call the servlet’s service method to proceed the request

Tomcat and the servlet can co-ordinate or communicate through the use of listener classes during the servlet’s lifecycle, which tracks the servlet for a variety of state changes.

To remove the servlet, Tomcat calls the servlets destroy method.

 

Ques. 14): In Tomcat, what is the difference between a host and a context?

Answer:

In Tomcat, the host is a component. It's a network name association for the server. On the other hand, context is an element that indicates a web application that is running on a certain virtual host. Web applications are built on top of a Web Application Archive (WAR) file or a corresponding directory that contains all of the unpacked content indicated in the servlet description.

 

Ques. 15): What Is The Distinction Between A Webserver And An Application Server?

Answer:

The main distinction between a web server and an application server is that a web server can only execute web applications, such as servlets and JSPs, and has just one container, the Web container, that is used to understand and execute web applications. The application server has the ability to run Enterprise applications, i.e. (servlets, jsps, and EJBs)

it is having two containers:

Web Container(for interpreting/executing servlets and jsps)

EJB container(for executing EJBs).

it can perform operations like load balancing , transaction demarcation etc.

 

Ques. 16): Apart from Apache Tomcat, what are the different kinds of Web Servers?

Answer:

There are many web servers as mentioned below:

LiteSpeed Web Server

GWS Web Server

Microsoft IIS Web Server

Nginx Web Server

Jigsaw Web Server

Sun Java System Web Server

Lighttpd Web Server

 

Ques. 17): How to limit upload size?

Answer:

I have a web application that allows users to upload files such as word documents, pdf and so on.  How do I limit file upload by users?

You can make use of the LimitRequestBody directive to limit upload file size.

<Directory "usr/local/apache2/uploads">

LimitRequestBody 9000

</Directory>

The value assigned to the LimitRequestBody allows Apache to accept and store file uploads of 9000 bytes by users. You can adjust the value based on the requirement.

 

Ques. 18): Explain how to use WAR files to deploy a web application.

Answer:

JSPs, servlets, and their associated files are placed under Tomcat's web applications directory in the appropriate subdirectories. You can combine all of the files in the web apps directory into a single compressed file with the extension.war. A web application can be run by placing a WAR file in the webapps directory. When a web server starts up, it extracts the contents of the WAR file and places them in the proper webapps sub-directories.

 

Ques. 19): How can an Apache Service be stopped by its control script?

Answer:

The Apache Service is controlled using a script called the apachectl.

So, to stop the service, we need to run the below-mentioned commands.

#apachectl stop [for Ubuntu based system]

# /etc/inid.t/httpd.stop [for red hat based system]

 

Ques. 20): What is the purpose of the Listen property in Apache Tomcat?

Listening is very important for Apache Tomcat and the developers.

If a developer has numerous IPs on the server, we must explicitly indicate IP and PORT in the Listen Drive if we want Apache to evaluate only one of them.

For example: 10.10.10.20

 

 

June 05, 2019

Top 50 Advance Java Interview Questions and Answers


Ques: 1. What do you understand by Private, Protected and Public?
 

Answer: 

Private, Protected and Public are the accessibility modifiers. Private is the most restrictive, while public is the least restrictive. There is no real difference between protected and the default type (also known as package protected) within the context of the same package, however the protected keyword allows visibility to a derived class in a different package. 

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Ques: 2. What is a java package? How is it used?

Answer: 

A Java package is a naming context for classes and interfaces.

  • A package is used to create a separate name space for groups of classes and interfaces.
  • Packages are used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.

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Ques: 3. What do you understand by EAR, JAR and WAR File?


Answer:
Enterprise Archives (EAR): An EAR file contains all the components that make up a J2EE application.

Java Archives (JAR): A JAR file encapsulates one or more Java classes, a manifest, and a descriptor. JAR files are the lowest level of archive. JAR files are used in J2EE for packaging EJBs and client-side Java Applications.

Web Archives (WAR): WAR files are like JAR files, except that they are specifically for web applications made from Servlets, JSPs, and supporting classes.

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Ques: 4. How Java Source Code files are named?

Answer: 

A source code file may contain at most one public class or interface. A Java source code file takes the name of a public class or interface that is defined within the file. Source code files use the .java extension.
If a public class or interface is defined within a source code file, then the source code file must take the name of the public class or interface. If no public class or interface is defined within a source code file, then the file must take on a name that is different than its classes and interfaces.


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Ques: 5. What do you understand by Numeric Promotion?

Answer: 

In numerical promotion, byte, char, and short values are converted to int values. It is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. if required, the int values are also converted to long values. The long and float values can be converted to double values.

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Ques: 6. What is the difference between Time Slicing and Preemptive Scheduling?

Answer: 

Under time slicing in java, a task executes for a predefined slice of time and then reenters the pool of ready tasks.
But under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states, or a higher priority task comes into existence.

The scheduler then determines which task should execute next, based on priority and other factors.

 

Ques: 7. What do you mean by a Task's Priority? How is it used in Scheduling?

Answer: 

A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks.


Ques: 8. What technologies are included in J2EE?

Answer: 

The various technologies in J2EE are:

  • Enterprise JavaBeansTM (EJBsTM).
  • JavaServer PagesTM (JSPsTM).
  • Java Servlets.
  • The Java Naming and Directory InterfaceTM (JNDITM).
  • The Java Transaction API (JTA).
  • CORBA.
  • The JDBCTM data access API.

 

Ques: 9. What is the main purpose of the Wait(), Notify() and Notifyall() methods in java?

Answer: 

These methods are used to provide an efficient way for threads to wait for a shared resource. When a thread in java executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods.

 

Ques: 10. What happens when you invoke a Thread's interrupt method while it is Sleeping or Waiting?

Answer: 

When a task's interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.

 

Ques: 11. What are the various restrictions placed on method overriding?

Answer:

  • The overriding method may not limit the access of the method it overrides.
  • Overridden methods must have the same name, argument list, and return type.
  • The overriding method may not throw any exceptions that may not be thrown by the overridden method.


Ques: 12. What do you understand by Java Swing?

Answer: 

Swing is basically a type of Toolkit which is GUI toolkit for Java. It is one part of the Java Foundation Classes (JFC). Swing includes graphical user interface (GUI) widgets such as text boxes, buttons, split-panes, and tables.
Swing supports pluggable look and feel, not by using the native platform's facilities, but by roughly emulating them. This means you can get any supported look and feel on any platform.
Swing widgets provide more sophisticated GUI components than the earlier Abstract Window Toolkit. Since they are written in pure Java, they run the same on all platforms. The advantage is uniform behavior on all platforms. The disadvantage of lightweight components is slower execution.


Ques: 13. What are the differences between Swing and AWT?

Answer: 

There are many differences between Swing and AWT:

  • AWT is heavy-weight components, but Swing is light-weight components.
  • AWT is OS dependent because it uses native components, But Swing components are OS independent.
  • Can change the look and feel in Swing which is not possible in AWT.
  • Swing takes less memory compared to AWT.
  • For drawing AWT uses screen rendering where Swing uses double buffering.

 

Ques: 14. What are the Types of Scaling?

Answer: 

In java, there are two types of scaling: Horizontal Scaling and Vertical Scaling.

Horizontal Scaling: When Clones of an application server are defined on multiple physical m/c, it is called Horizontal Scaling. The objective is to use more than one less powerful m/c more efficiently.

Vertical Scaling: When multiple server clones of an application server are defined on the same physical m/c, it is called Vertical Scaling. The objective is to use the processing power of that m/c more efficiently.

 

Ques: 15. What are the types of Class Loaders in java?

Answer: 

In java, there are three types of class loader as bootstarp class loader, extension class loader and system class loader.

Bootstrap Class Loader: Bootstrap class loader loads java’s core classes like java.lang, java.util etc. These are classes that are part of java runtime environment. Bootstrap class loader is native implementation and so they may differ across different JVMs.

 Extensions Class Loader: JAVA_HOME/jre/lib/ext contains jar packages that are extensions of standard core java classes. Extensions class loader loads classes from this ext folder. Using the system environment property java.ext.dirs you can add ‘ext’ folders and jar files to be loaded using extensions class loader.

System Class Loader: Java classes that are available in the java classpath are loaded using System class loader.



Ques: 16. What are differences between the boolean & operator and the && operator?

Answer: 

If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated.
If the first operand returns a value of true, then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.

 

Ques: 17. What do you mean by Casting?

Answer: 

In java, there are two types of casting:

1). casting between primitive numeric types: Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values.

2). casting between object references: Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.


Ques: 18. How does a Try statement determine which Catch clause should be used to handle an exception?

Answer: 

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.

 

Ques: 19. What will happens if Remove( ) is never invoked on a session bean?

Answer: 

In case of stateful session bean, the bean may be kept in cache till either the session times out, in which case the bean is removed or when there is a requirement for memory in which case the data is cached and the bean is sent to free pool.
In case of a stateless session bean it may not matter if we call or not as in both cases nothing is done. The number of beans in cache is managed by the container.


Ques: 20. What Is Java Reflection Api?

Answer: 

Reflection is one of the most powerful api which help to work with classes, methods and variables dynamically. Basically, it inspects the class attributes at runtime. Also, we can say it provides a metadata about the class.

 

Ques: 21. What is the Collection API in java?

Answer: 

The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces.

Example of classes: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.

Example of interfaces: Collection, Set, List and Map.



Ques: 22. What is the difference between Session and Entity Beans?

Answer: 

An entity bean represents persistent global data from the database; a session bean represents transient user-specific data that will die when the user disconnects (ends his session). Generally, the session beans implement business methods that call entity beans .


Ques: 23. What do you understand by Abstract Schema in java?

Answer: 

In java, you can specify the name of the Abstract schema name in the deployment descriptor. The queries written in EJB QL for the finder methods references this name. It is a part of an entity bean’s deployment descriptor which defines the bean’s persistent fields and their relationship. Abstract schema is specified for entity beans with container managed persistence. The information provided in this Abstract Schema is used by the container for persistence management and relationship management.


Ques: 24. What is the use of the Finally block? Is Finally block in Java guaranteed to be called? When will it is not called?

Answer:

The code in finally block will execute even if an exception is occurred. Finally, is the block of code that executes always. Finally block is NOT called in following conditions:

  • If the JVM exits while the try or catch code is being executed, then the finally block may not execute. This may happen due to System.exit() call.
  • if the thread executing the try or catch code is interrupted or killed, the finally block may not execute even though the application as a whole continues.
  • If an exception is thrown in finally block and not handled, then remaining code in finally block may not be executed.


Ques: 25. What do you mean by Local Interface. How values will be passed to them?

Answer: 

An EJB can use local client view only if it is really guaranteed that other enterprise beans or clients will only address the bean within a single JVM. With local client view, you can do pass-by-reference, which means your bean, as well as the client, will work directly with one copy of the data. Any changes made by the bean will be seen by the client and vice versa. Pass-by-reference eliminates time/system expenses for copying data variables, which provides a performance advantage.


Ques: 26. What is the main difference between Serializable and Externalizable Interfaces?

Answer: 

Both interfaces are used for implementing serialization. But, the basic difference is Serializable interface does not have any method (it’s a marker interface) and Externalizable interface having 2 methods such as readExternal() and writeExternal(). Serializable interface is the super interface for Externalizable interface.



Ques: 27. What is the relation between Local Interfaces and Container-managed relationships?

Answer: 

To be the target of a container-managed relationship, an entity bean with container-managed persistence must provide a local interface. Entity beans that have container-managed relationships with other entity beans, must be accessed in the same local scope as those related beans, and therefore typically provide a local client view.

 

Ques: 28. What are the differences between Creating String as New() and Literal?

Answer: 

When we create string with new() Operator, it’s created in heap and not added into string pool while String created using literal are created in String pool itself which exists in PermGen area of heap.
String s = new String(“Test”);
It does not put the object in String pool, we need to call String.intern() method which is used to put  them into String pool explicitly. its only when you create String object as String literal e.g. String s = “Test” Java automatically put that into String pool.


Ques: 29. What is the main difference between Final, Finally And Finalize?

Answer: 
Final is used to apply restrictions on class, method and variable. Final class can’t be inherited, final method can’t be overridden, and final variable value can’t be changed.

Finally is used to place important code, it will be executed whether exception is handled or not.
Finalize is used to perform clean up processing just before object is garbage collected.

 

Ques: 30. How can an Object's Finalize() Method be invoked while it is reachable?

Answer: 

An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.

 

Ques: 31. What do you mean by an Object’s Lock? Which Object Have Locks?

Answer: 

A thread may execute a synchronized method of an object only after it has acquired the object’s lock. An object’s lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. All objects and classes have locks. A class’s lock is acquired on the class’s Class object.


Ques: 32. What are the uses of Observer and Observable?

Answer: 

Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.

 

Ques: 33. How ConcurrentHashMap Works?

Answer:

Basically, ConcurrentHashMap locks each of the box (by default 16) which can be locked independently and thread safe for operation. The basic design of ConcurrentHashMap is to handling threading. And it does not expose the internal lock process.

 

Ques: 34. What are Transient Variables in java?

Answer: 

In Java, Transient variables can’t be serialized. For example, if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can’t be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.


Ques: 35. What do you understand by JFC?

Answer: 

JFC stands for Java Foundation Classes. The Java Foundation Classes (JFC) are a set of Java class libraries provided as part of Java 2 Platform, Standard Edition (J2SE) to support building graphics user interface (GUI) and graphics functionality for client applications that will run on popular platforms such as Microsoft Windows, Linux, and Mac OSX.


Ques: 36. What is the main difference between Find and Select methods In EJB?

Answer: 

A select method can return a persistent field (or a collection thereof) of a related entity bean. A finder method can return only a local or remote interface (or a collection of interfaces).

A select method is defined in the entity bean class. For bean-managed persistence, a finder method is defined in the entity bean class, but for container-managed persistence it is not.
Because it is not exposed in any of the local or remote interfaces, a select method cannot be invoked by a client. It can be invoked only by the methods implemented within the entity bean class. A select method is usually invoked by either a business or a home method.


Ques: 37. If some new data has entered in the database, how can a servlet refresh automatically?

Answer: 

It depends on the scenario, how you can handle them. You need to handle this in dao layer, when doing insert operation, you can call a utility method which will load the context ServletContextListener. Because, servlets are basically used for handling request and give the response.


Ques: 38. What do you mean by In-memory replication?

Answer: 

The process by which the contents in the memory of one physical m/c are replicated in all the m/c in the cluster is called in-memory replication.


Ques: 39. What do you understand by synchronization? Why is it so Important?

Answer: 

In respect of multithreading, synchronization is the capability to control the access of multiple threads to shared resources. In the absence of synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.

 

Ques: 40. How many Bits are used to represent Unicode, ASCII, UTF-16 and UTF-8 characters?

Answer: 

Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. Unicode requires 16 bits and ASCII require 7 bits. UTF-8 represents characters using 8, 16, and 18 bits patterns. UTF-16 uses 16-bit and larger bit patterns.



Ques: 41. What is a Clone in java?

Answer: 

In java, the copies of a server group are called Clones. But unlike a Server Group Clones are associated with a node and are real server process running in that node.


Ques: 42. How does the Garbage Collection guarantee that a program will not run out of memory?

Answer: 

In java, garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection.


Ques: 43. What do you mean by AWT?

Answer: 

AWT is stands for Abstract Window Toolkit. AWT enables programmers to develop Java applications with GUI components, such as windows, and buttons. The Java Virtual Machine (JVM) is responsible for translating the AWT calls into the appropriate calls to the host operating system.


Ques: 44. What Advantage do Java's Layout Managers provide over traditional Windowing Systems?

Answer: 

Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accommodate platform-specific differences among windowing systems.


Ques: 45. Is Decorator an EJB design pattern?

Answer: 

Decorator design pattern is not an EJB design pattern. It is the one which exhibits very low-level runtime polymorphism, for the specific and single object (Instance of the class). But not for at least for a class. It is the stuff to add specific functionality to a single & pointed object and leaves others like it unmodified. It is having close similarities like AspectJ stuff, but not with EJB stuff.


Ques: 46. What is the main purpose of the Enableevents() method?

Answer: 

The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event.
The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.


Ques: 47. What is the main difference between Paint() and PaintComponent()?

Answer: 

The main point is that the paint() method invokes three methods in the following order:

  • PaintComponent()
  • PaintBorder()
  • paintChildren()

As a general rule, in Swing, we should be overriding the paintComponent method unless we know what we are doing paintComponent() paints only component (panel) but paint() paints component and all its children.


Ques: 48. What do you understand by double buffering ?

Answer: 

Double buffering is the process of using two buffers rather than one to temporarily hold data being moved to and from an I/O device. Double buffering increases data transfer speed because one buffer can be filled while the other is being emptied.


Ques: 49. What is the main difference between the File and RandomAccessFile Classes?

Answer: 

The File class encapsulates the files and directories of the local file system.
The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.

 

Ques: 50. Can you Name some of the Layoutmanagers In Java?

Answer: 

Some of the LayoutManagers in java are:

  • Flow Layout Manager
  • Grid Layout Manager
  • Box Layout Manager
  • Border Layout Manager
  • Card Layout Manager
  • GridBag Layout Manager