Cloud Computing-Q/A-interview

1. What is cloud computing?

The cloud computing is the computing which is completely based on the Internet. It can also be defined as the next stage in the evolution of the Internet. The cloud computing uses the cloud (Internet) that provides the way to deliver the services whenever and wherever the user of the cloud needs. Companies use the cloud computing to fulfill the needs of their customers, partners, and providers. The cloud computing includes vendors, partners, and business leaders as the three major contributors. The vendors are the one who provide applications and their related technology, infrastructure, hardware, and integration.

The partners are those who offer cloud services demand and provide support service to the customers. The business leaders are the ones who use or evaluate the cloud service provided by the partners. The cloud computing enables the companies to treat their resources as a pool and not as independent resources.

2. What is a cloud?

A cloud is a combination of hardware, networks, storage, services, and interfaces that helps in delivering computing as a service. It has broadly three users which are end user, business management user, and cloud service provider. The end user is the one who uses the services provided by the cloud. The business management user in the cloud takes the responsibility of the data and the services provided by the cloud. The cloud service provider is the one who takes care or is responsible for the maintenance of the IT assets of the cloud. The cloud acts as a common center for its users to fulfill their computing needs.

3. What are the basic characteristics of cloud computing?

The four basic characteristics of cloud computing are given as follows:

• Elasticity and scalability.
• Self-service provisioning and automatic de-provisioning.
• Standardized interfaces.
• Billing self-service based usage model.

4. What is a Cloud Service?

A cloud service is a service that is used to build cloud applications. This service provides the facility of using the cloud application without installing it on the computer. It reduces the maintenance and support of the application as compared to those applications that are not developed using the cloud service. The different kinds of users can use the application from the cloud service, which may be public or private application.

5. What are main features of cloud services?

Some important features of the cloud service are given as follows:

• Accessing and managing the commercial software.
• Centralizing the activities of management of software in the Web environment.
• Developing applications that are capable of managing several clients.
• Centralizing the updating feature of software that eliminates the need of downloading the upgrades.

6. How many types of deployment models are used in cloud?

There are 4 types of deployment models used in cloud:

1. Public cloud
2. Private cloud
3. Community cloud
4. Hybrid cloud  

7. What is the AppFabric component?

The AppFabric component is used to create access control and distribute messages across clouds and enterprises. It has a service-oriented architecture, and can be considered as the backbone of the Windows Azure platform. It provides connectivity and messaging among distributed applications. It also has the capabilities of integrating the applications and the business processes between cloud services and also between cloud services and global applications.

The AppFabric component provides a development environment that is integrated with Visual Studio 2010.TheWindows Communication Foundation (WCF) services built in VS 2010 can be published on cloud from the Visual Studio design environment.

The two important services of AppFabric are as follows:

• Access Control Service (ACS) - Allows rules-driven and claims-based access control for distributed applications. These claims-based rules and authorization roles can be defined in the cloud for accessing on-premise and cloud services. The claim can be a user or application attribute, which the service application expects, such as e-mail address, phone number, password, and role, for appropriate access control. When any application wants to use the Web service, it sends the required claims to ACS for requesting a token. ACS converts the input claims into output claims by following the rules of mapping. These rules are created during the configuration of ACS. The ACS issues a token containing the output claims for the consumer application. This application uses this token in the request header and sends to the Web service. This service validates the claims in the token and gives suitable access to the user.
• Service bus - Provides messaging between cross-enterprise and cross-cloud scenarios. It provides publish/subscribe, point-to-point, and queues message patterns for exchange of messages across distributed applications in the cloud. It integrates with the Access Control service to establish secure relay and communication.

8. Why does an organization need to manage the workloads?

The workload can be defined as an independent service or a set of code that can be executed. It can be everything from a data-intensive workload to storage or a transaction processing workload and does not rely upon the outside elements. The workload can be considered as a small or complete application.

The organization manages workloads because of the following reasons:

• To know how their applications are running.
• To know what functions they are performing.
• To know the charges of the individual department according to the use of the service.

9. Which services are provided by Window Azure operating system?

Windows Azure provides three core services which are given as follows:

• Compute
• Storage
• Management

10. Explain hybrid and community cloud.

The hybrid cloud consists of multiple service providers. This model integrates various cloud services for Hybrid Web hosting. It is basically a combination of private and public cloud features. It is used by the company when a company has requirements for both the private and public clouds. Consider an example when an organization wants to implement the SaaS (Software as a Service) application throughout the company. The implementation requires security that can be provided by the private cloud used inside the firewall. The additional security can be provided by the VPN on requirement. Now, the organization has both the private and public cloud features.

The community cloud provides a number of benefits, such as privacy and security. This model, which is quite expensive, is used when the organizations having common goals and requirements are ready to share the benefits of the cloud service.

11. Explain public and private cloud.

The public cloud (or external cloud) is freely available for access. You can use a public cloud to collect data of the purchasing of items from a Web site on the Internet. You can also use public cloud for the reasons, which are given as follows:

• Helps when an application is to be used by a large number of people, such as an e-mail application, on the Internet.
• Helps when you want to test the application and also needs to develop the application code.
• Helps when you want to implement the security for the application.
• Helps when you want to increase the computing capacity.
• Helps when you are working on the projects in collaboration.
• Helps when you are developing the project on an ad-hoc basis by using PaaS.

The private cloud allows the usage of services by a single client on a private network. The benefits of this model are data security, corporate governance, and reliability concerns. The private cloud is used by the organization when it has a huge, well-run data center having a lot of spare capacity. It is also used when an organization is providing IT services to its clients and the data of organization is highly important. It is best suited when the requirements are critical.

The characteristics of this model are given as follows:

• Provides capability to internal users and allows provision of services.
• Automates the tasks of management and provides the billing of consumption of a particular service.
• Offers a well-managed environment.
• Enables the optimization of computational resources, such as servers.
• Manages the workload of the hardware.
• Offers self-service based provisioning of hardware resources and software.

12. Give a brief introduction of Windows Azure operating system.

The Windows Azure operating system is used for running cloud services on the Windows Azure platform, as it includes necessary features for hosting your services in the cloud. It also provides runtime environment that consists of Web server, computational services, basic storage, queues, management services, and load balancers. The operating system provides development. Fabric for development and testing of services before their deployment on the Windows Azure in the cloud.

13. What are the advantages of cloud services?

Some of the advantages of cloud service are given as follows:

• Helps in the utilization of investment in the corporate sector; and therefore, is cost saving.
• Helps in the developing scalable and robust applications. Previously, the scaling took months, but now, scaling takes less time.
• Helps in saving time in terms of deployment and maintenance.

Java Threads Interview Questions

What are three ways in which a thread can enter the waiting state?

Or

What are different ways in which a thread can enter the waiting state?

A thread can enter the waiting state by the following ways:
1. Invoking its sleep() method,
2. By blocking on I/O
3. By unsuccessfully attempting to acquire an object’s lock
4. By invoking an object’s wait() method.
5. It can also enter the waiting state by invoking its (deprecated) suspend() method.

What is the difference between yielding and sleeping?

When a task invokes its yield() method, it returns to the ready state, either from waiting, running or after its creation. When a task invokes its sleep() method, it returns to the waiting state from a running state.

How to create multithreaded program? Explain different ways of using thread? When a thread is created and started, what is its initial state?

Or

Extending Thread class or implementing Runnable Interface. Which is better?

You have two ways to do so. First, making your class “extends” Thread class. The other way is making your class implement “Runnable” interface. The latter is more advantageous, cause when you are going for multiple inheritance, then only interface can help. . If you are already inheriting a different class, then you have to go for Runnable Interface. Otherwise you can extend Thread class. Also, if you are implementing interface, it means you have to implement all methods in the interface. Both Thread class and Runnable interface are provided for convenience and use them as per the requirement. But if you are not extending any class, better extend Thread class as it will save few lines of coding. Otherwise performance wise, there is no distinguishable difference. A thread is in the ready state after it has been created and started.

What is mutual exclusion? How can you take care of mutual exclusion using Java threads?

Mutual exclusion is a phenomenon where no two processes can access critical regions of memory at the same time. Using Java multithreading we can arrive at mutual exclusion. For mutual exclusion, you can simply use the synchronized keyword and explicitly or implicitly provide an Object, any Object, to synchronize on. The synchronized keyword can be applied to a class, to a method, or to a block of code. There are several methods in Java used for communicating mutually exclusive threads such as wait( ), notify( ), or notifyAll( ). For example, the notifyAll( ) method wakes up all threads that are in the wait list of an object.

What is the difference between preemptive scheduling and time slicing?

Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then re-enters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

What invokes a thread’s run() method?

After a thread is started, via its start() method of the Thread class, the JVM invokes the thread’s run() method when the thread is initially executed.

What is the purpose of the wait(), notify(), and notifyAll() methods?

The wait(), notify() and notifyAll() methods are used to provide an efficient way for thread inter-communication.

What is thread? What are the high-level thread states?

Or

What are the states associated in the thread?

A thread is an independent path of execution in a system. The high-level thread states are ready, running, waiting and dead.

What is deadlock?

When two threads are waiting for each other and can’t proceed until the first thread obtains a lock on the other thread or vice versa, the program is said to be in a deadlock.

How does multithreading take place on a computer with a single CPU?

The operating system’s task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.

What are synchronized methods and synchronized statements?

Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method’s object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.

Can Java object be locked down for exclusive use by a given thread?

Or

What happens when a thread cannot acquire a lock on an object?

Yes. You can lock an object by putting it in a “synchronized” block. The locked object is inaccessible to any thread other than the one that explicitly claimed it. If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object’s lock, it enters the waiting state until the lock becomes available.

What’s the difference between the methods sleep() and wait()?

The sleep method is used when the thread has to be put aside for a fixed amount of time. Ex: sleep(1000), puts the thread aside for exactly one second. The wait method is used to put the thread aside for up to the specified time. It could wait for much lesser time if it receives a notify() or notifyAll() call. Ex: wait(1000), causes a wait of up to one second. The method wait() is defined in the Object and the method sleep() is defined in the class Thread.

What is the difference between process and thread?

A thread is a separate path of execution in a program. A Process is a program in execution.

What is daemon thread and which method is used to create the daemon thread?

Daemon threads are threads with low priority and runs in the back ground doing the garbage collection operation for the java runtime system. The setDaemon() method is used to create a daemon thread. These threads run without the intervention of the user. To determine if a thread is a daemon thread, use the accessor method isDaemon()

When a standalone application is run then as long as any user threads are active the JVM cannot terminate, otherwise the JVM terminates along with any daemon threads which might be active. Thus a daemon thread is at the mercy of the runtime system. Daemon threads exist only to serve user threads.

What do you understand by Synchronization?

Or

What is synchronization and why is it important?

Or

Describe synchronization in respect to multithreading?

Or

What is synchronization?

With respect to multithreading, Synchronization is a process of controlling the access of shared resources by the multiple threads in such a manner that only one thread can access a particular resource at a time. In non synchronized multithreaded application, it is possible for one thread to modify a shared object while another thread is in the process of using or updating the object’s value. Synchronization prevents such type of data corruption which may otherwise lead to dirty reads and significant errors.
E.g. synchronizing a function:
public synchronized void Method1 () {
// method code.
}
E.g. synchronizing a block of code inside a function:
public Method2 (){
synchronized (this) {
// synchronized code here.
}
}

When you will synchronize a piece of your code?

When you expect that your shared code will be accessed by different threads and these threads may change a particular data causing data corruption, then they are placed in a synchronized construct or a synchronized method.

Why would you use a synchronized block vs. synchronized method?

Synchronized blocks place locks for shorter periods than synchronized methods.

What is an object’s lock and which objects have locks?

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

Can a lock be acquired on a class?

Yes, a lock can be acquired on a class. This lock is acquired on the class’s Class object.

What state does a thread enter when it terminates its processing?

When a thread terminates its processing, it enters the dead state.

How would you implement a thread pool?

public class ThreadPool implements ThreadPoolInt

This class is an generic implementation of a thread pool, which takes the following input

a) Size of the pool to be constructed

b) Name of the class which implements Runnable and constructs a thread pool with active threads that are waiting for activation. Once the threads have finished processing they come back and wait once again in the pool.

This thread pool engine can be locked i.e. if some internal operation is performed on the pool then it is preferable that the thread engine be locked. Locking ensures that no new threads are issued by the engine. However, the currently executing threads are allowed to continue till they come back to the passivePool.

Is there a separate stack for each thread in Java?

Yes. Every thread maintains its own separate stack, called Runtime Stack but they share the same memory. Elements of the stack are the method invocations,
called activation records or stack frame. The activation record contains pertinent information about a method like local variables.

Java Wrapper Classes Interview Questions

What are Wrapper Classes? Describe the wrapper classes in Java.

Wrapper classes are classes that allow primitive types to be accessed as objects. Wrapper class is wrapper around a primitive data type.

Following table lists the primitive types and the corresponding wrapper classes:

Primitive	Wrapper
Boolean	java.lang.Boolean
Byte	java.lang.Byte
Char	java.lang.Character
double	java.lang.Double
Float	java.lang.Float
Int	java.lang.Integer
Long	java.lang.Long
Short	java.lang.Short
Void	java.lang.Void

Java Swing Interview Questions

What is the difference between Swing and AWT components?

AWT components are heavy-weight, whereas Swing components are lightweight. Hence Swing works faster than AWT. Heavy weight components depend on the local windowing toolkit. For example, java.awt.Button is a heavy weight component. Pluggable look and feel possible using java Swing. Also, we can switch from one look and feel to another at runtime in swing which is not possible in AWT.

Name the containers which use Border Layout as their default layout?

window, Frame and Dialog classes.

Name Container classes.

Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane

How can a GUI component handle its own events?

A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.

What is the difference between the paint() and repaint() methods?

The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.

Which package has light weight components?

javax.Swing package contains light weight components. All components in Swing, except JApplet, JDialog, JFrame and JWindow are lightweight components.

What are peerless components?

The peerless components are called light weight components.

What is a Container in a GUI?

A Container contains and arranges other components (including other containers) through the use of layout managers, which use specific layout policies to determine where components should go as a function of the size of the container.

How are the elements of a GridBagLayout organized?

Or

What is a layout manager and what are different types of layout managers available in java Swing?

Or

How are the elements of different layouts organized?

A layout manager is an object that is used to organize components in a container. The different layouts available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout.

FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left to right fashion.

BorderLayout: The elements of a BorderLayout are organized at the borders (North, South, East and West) and the center of a container.

CardLayout: The elements of a CardLayout are stacked, on top of the other, like a deck of cards.

GridLayout: The elements of a GridLayout are of equal size and are laid out using the square of a grid.

GridBagLayout: The elements of a GridBagLayout are organized according to a grid. However, the elements may be different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.

What advantage do Java’s layout managers provide over traditional windowing systems?

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.

What method is used to specify a container’s layout?

The setLayout() method is used to specify a container’s layout. For example, setLayout(new FlowLayout()); will be set the layout as FlowLayout.

Which Container method is used to cause a container to be laid out and redisplayed?

validate()

Name Component subclasses that support painting.

The Canvas, Frame, Panel, and Applet classes support painting.

What is the purpose of the enableEvents() method?

The enableEvents() method is used to enable an event for a particular component. 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.

What is the difference between a Window and a Frame?

The Frame class extends Window to define a main application window that can have a menu bar.

What do heavy weight components mean?

Heavy weight components like Abstract Window Toolkit (AWT) depend on the local windowing toolkit. For example, java.awt .Button is a heavy weight component.

What is the difference between a Scrollbar and a ScrollPane?

A Scrollbar is just a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.

What is the preferred size of a component?

The preferred size of a component is the minimum component size that will allow the component to display normally.

Which containers use a FlowLayout as their default layout?

The Panel and Applet classes use the FlowLayout as their default layout.

DB Interview Questions

Q:
What is SQL?

A: SQL stands for 'Structured Query Language'.
 


Q:
What is SELECT statement?

A: The SELECT statement lets you select a set of values from a table in a database. The values selected from the database table would depend on the various conditions that are specified in the SQL query.
 


Q:
How can you compare a part of the name rather than the entire name?

A: SELECT * FROM people WHERE empname LIKE '%ab%'
Would return a recordset with records consisting empname the sequence 'ab' in empname .
 


Q:
What is the INSERT statement?

A: The INSERT statement lets you insert information into a database.
 


Q:
How do you delete a record from a database?

A: Use the DELETE statement to remove records or any particular column values from a database.
 


Q:
How could I get distinct entries from a table?

A: The SELECT statement in conjunction with DISTINCT lets you select a set of distinct values from a table in a database. The values selected from the database table would of course depend on the various conditions that are specified in the SQL query. Example
SELECT DISTINCT empname FROM emptable
 


Q:
How to get the results of a Query sorted in any order?

A: You can sort the results and return the sorted results to your program by using ORDER BY keyword thus saving you the pain of carrying out the sorting yourself. The ORDER BY keyword is used for sorting.

SELECT empname, age, city FROM emptable ORDER BY empname
 

Q:
How can I find the total number of records in a table?

A:
You could use the COUNT keyword , example

SELECT COUNT(*) FROM emp WHERE age>40

 


Q:
What is GROUP BY?

A: The GROUP BY keywords have been added to SQL because aggregate functions (like SUM) return the aggregate of all column values every time they are called. Without the GROUP BY functionality, finding the sum for each individual group of column values was not possible.
 


Q:
What is the difference among "dropping a table", "truncating a table" and "deleting all records" from a table.

A: Dropping :  (Table structure  + Data are deleted), Invalidates the dependent objects ,Drops the indexes
Truncating:  (Data alone deleted), Performs an automatic commit, Faster than delete

Delete : (Data alone deleted), Doesn’t perform automatic commit

 


Q:
What are the Large object types suported by Oracle?

A: Blob and Clob.
 


Q:
Difference between a "where" clause and a "having" clause.

A: Having clause is used only with group functions whereas Where is not used with.
 

Q:
What's the difference between a primary key and a unique key?

A:
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.

 


Q:
What are cursors? Explain different types of cursors. What are the disadvantages of cursors? How can you avoid cursors?

A:
Cursors allow row-by-row prcessing of the resultsets.

Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See books online for more information.

Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network roundtrip, where as a normal SELECT query makes only one rowundtrip, however large the resultset is. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Furthere, there are restrictions on the SELECT statements that can be used with some types of cursors.

Most of the times, set based operations can be used instead of cursors.

 

Q:
What are triggers? How to invoke a trigger on demand?

A: Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table.
Triggers can't be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, DELETE) happens on the table on which they are defined.

Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster.


Q:
What is a join and explain different types of joins.

A:
Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table.

Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.

 


Q:
What is a self join?

A: Self join is just like any other join, except that two instances of the same table will be joined in the query.
 

Java Interview Questions

Q:
What is the difference between an Interface and an Abstract class?

A: An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.
.
 


Q:
What is the purpose of garbage collection in Java, and when is it used?

A: The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used.
 

Q:
Describe synchronization in respect to multithreading.

A: With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchonization, it is possible for one thread to modify a shared variable while another thread is in the process of using or updating same shared variable. This usually leads to significant errors.
 


Q:
Explain different way of using thread?

A: The thread could be implemented by using runnable interface or by inheriting from the Thread class. The former is more advantageous, 'cause when you are going for multiple inheritance..the only interface can help.
 


Q:
What are pass by reference and passby value?

A: Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.
 


Q:
What is HashMap and Map?

A: Map is Interface and Hashmap is class that implements that.
 


Q:
Difference between HashMap and HashTable?

A: The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesnt allow). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is unsynchronized and Hashtable is synchronized.
 


Q:
Difference between Vector and ArrayList?

A: Vector is synchronized whereas arraylist is not.
 


Q:
Difference between Swing and Awt?

A: AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works faster than AWT.
 


Q:
What is the difference between a constructor and a method?

A: A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.
 


Q:
What is an Iterator?

A: Some of the collection classes provide traversal of their contents via a java.util.Iterator interface. This interface allows you to walk through a collection of objects, operating on each object in turn. Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator.
 


Q:
State the significance of public, private, protected, default modifiers both singly and in combination and state the effect of package relationships on declared items qualified by these modifiers.

A: public : Public class is visible in other packages, field is visible everywhere (class must be public too)
private : Private variables or methods may be used only by an instance of the same class that declares the variable or method, A private feature may only be accessed by the class that owns the feature.
protected : Is available to all classes in the same package and also available to all subclasses of the class that owns the protected feature.This access is provided even to subclasses that reside in a different package from the class that owns the protected feature.
default :What you get by default ie, without any access modifier (ie, public private or protected).It means that it is visible to all within a particular package.
 


Q:
What is an abstract class?

A: Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is abstract may not be instantiated (ie, you may not call its constructor), abstract class may contain static data. Any class with an abstract method is automatically abstract itself, and must be declared as such.
A class may be declared abstract even if it has no abstract methods. This prevents it from being instantiated.
 


Q:
What is static in java?

A: Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class.Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can't override a static method with a nonstatic method. In other words, you can't change a static method into an instance method in a subclass.


Q:
What is final?

A: A final class can't be extended ie., final class may not be subclassed. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant).