Interview Questions.

Question 1. What Is The Purpose Of Garbage Collection In Java, And When Is It Used?

Answer :

The purpose of garbage collection is to identify and discard objects which can be not needed by way of a application in order that their resources may be reclaimed and reused. A Java object is challenge to rubbish series whilst it becomes unreachable to the program in which it's far used.

Question 2. What If The Main Method Is Declared As Private?

Answer :

The application compiles nicely however at runtime it will deliver “Main technique no longer public.” message.

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Question 3. What If I Write Static Public Void Instead Of Public Static Void?

Answer :

Program compiles and runs well.

Question 4. What If I Do Not Provide The String Array As The Argument To The Method?

Answer :

Program compiles but throws a runtime mistakes “NoSuchMethodError”.

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Question five. What Is The First Argument Of The String Array In Main Method?

Answer :

The String array is empty. It does no longer have any element. This is not like C/C++ wherein the primary element with the aid of default is the program call

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Question 6. How Can One Prove That The Array Is Not Null But Empty Using One Line Of Code?

Answer :

Print args.Period. It will print 0. That method it is empty. But if it would have been null then it'd have thrown a Null Pointer Exception on trying to print args.Duration.

Question 7. What Are Checked And Unchecked Exception?

Answer :

A checked exception is some subclass of Exception (or Exception itself), excluding elegance Runtime Exception and its subclasses. Making an exception checked forces client programmers to cope with the opportunity that the exception could be thrown. Eg, IOException thrown with the aid of java.Io.FileInputStream’s study() approach· Unchecked exceptions are Runtime Exception and any of its subclasses. Class Error and its subclasses also are unchecked. With an unchecked exception, however, the compiler doesn’t force patron programmers either to catch the exception or claim it in a throws clause. In fact, customer programmers may not even know that the exception might be thrown. Eg, StringIndexOutOfBoundsException thrown via String’s char At () approach· Checked exceptions have to be stuck at assemble time. Runtime exceptions do not want to be. Errors regularly can't be.

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Question 8. What Are Different Types Of Inner Classes?

Answer :

Nested pinnacle-stage training, Member training, Local training, Anonymous instructions Nested top-degree lessons- If you declare a category inside a class and specify the static modifier, the compiler treats the elegance much like any other top-level class. Any class out of doors the putting forward magnificence accesses the nested magnificence with the maintaining magnificence call performing further to a bundle. Eg, outer. Inner. Top-degree inner training implicitly have get right of entry to handiest to static variables. There can also be inner interfaces. These are of the nested top-stage variety.

Member lessons – Member internal classes are much like different member methods and member variables and get entry to to the member magnificence is constrained, just like strategies and variables. This way a public member elegance acts further to a nested pinnacle-level class. The primary difference between member lessons and nested top-degree classes is that member instructions have get right of entry to to the particular example of the enclosing elegance.

Local classes – Local training are like neighborhood variables, particular to a block of code. Their visibility is simplest in the block in their statement. For the class to be useful past the declaration block, it would want to put in force a extra publicly available interface. Because neighborhood instructions are not individuals, the modifiers public, included, non-public, and static aren't usable.

Anonymous training – Anonymous inner classes amplify neighborhood internal instructions one level similarly. As nameless instructions haven't any call, you can't provide a constructor.

Question nine. What Is The Difference Between An Interface And An Abstract Class?

Answer :

An abstract elegance could have instance techniques that enforce a default conduct. An Interface can best declare constants and instance methods, however can't implement default conduct and all methods are implicitly abstract. An interface has all public members and no implementation. An summary elegance is a category which might also have the usual flavors of class members (non-public, included, and many others.), but has some abstract methods.

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Question 10. Describe Synchronization In Respect To Multithreading?

Answer :

With admire to multithreading, synchronization is the functionality to manipulate the get entry to of more than one threads to shared resources. Without synchronization, it's far feasible for one thread to alter a shared variable whilst another thread is within the technique of the usage of or updating equal shared variable. This usually leads to good sized mistakes.

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Question 11. What Are Pass By Reference And Pass By Value?

Answer :

Pass through Reference way the passing the address itself in preference to passing the price. Passby Value means passing a copy of the cost to be surpassed.

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Question 12. What Is Hashmap And Map?

Answer :

Map is Interface and Hashmap is magnificence that implements that.

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Question 13. Difference Between Hashmap And Hashtable?

Answer :

The HashMap magnificence is kind of equal to Hashtable, besides that it's far unsynchronized and allows nulls. (HashMap allows null values as key and cost whereas Hashtable doesnt allow). HashMap does not assure that the order of the map will stay constant over the years. HashMap is unsynchronized and Hashtable is synchronized.

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Question 14. Difference Between Vector And Arraylist?

Answer :

Vector is synchronized while arraylist is not.

Question 15. Difference Between Swing And Awt?

Answer :

AWT are heavy-weight additives. Swings are light-weight components. Hence swing works faster than AWT.

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Question 16. What Is The Difference Between A Constructor And A Method?

Answer :

A constructor is a member function of a category this is used to create gadgets of that magnificence. It has the identical name because the class itself, has no go back kind, and is invoked the use of the new operator. A approach is an ordinary member characteristic of a class. It has its very own call, a go back type (which can be void), and is invoked using the dot operator.

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Question 17. What Is An Iterator?

Answer :

Some of the collection instructions offer traversal of their contents thru a java.Util.Iterator interface. This interface allows you to walk through a collection of objects, operating on every object in turn. Remember while the usage of Iterators that they include a photo of the collection at the time the Iterator was acquired; generally, it isn't always really helpful to modify the gathering itself at the same time as traversing an Iterator.

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Question 18. What Is An Abstract Class?

Answer :

Abstract class have to be extended/subclassed (to be useful). It serves as a template. A class that is summary won't be instantiated (ie, you may now not call its constructor), summary magnificence may additionally include static information. Any class with an summary method is robotically abstract itself, and must be declared as such. A magnificence can be declared abstract although it has no abstract methods. This prevents it from being instantiated.

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Question 19. What Is Static In Java?

Answer :

Static means one in line with elegance, not one for each item irrespective of how many instance of a class would possibly exist. This approach that you could use them with out developing an instance of a category.Static strategies are implicitly final, due to the fact overriding is performed based at the type of the object, and static techniques are attached to a category, no longer an object. A static method in a superclass can be shadowed with the aid of any other static method in a subclass, if the original approach changed into no longer declared final. However, you can’t override a static technique with a non-static approach. In other phrases, you could’t alternate a static approach into an example technique in a subclass.

Question 20. What Is Final?

Answer :

A final elegance can’t be prolonged ie., final magnificence won't be subclasses. A final technique can’t be overridden while its class is inherited. You can’t trade fee of a very last variable (is a consistent)

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Question 21. Are The Imports Checked For Validity At Compile Time? E.G. Will The Code Containing An Import Such As Java.Lang.Abcd Compile?

Answer :

Yes, the imports are checked for the semantic validity at bring together time. The code containing above line of import will now not assemble. It will throw an errors saying, can not clear up image

image: magnificence ABCD

place: bundle io

import java.Io.ABCD;

Question 22. What Is The Difference Between Declaring A Variable And Defining A Variable?

Answer :

In statement, we simply point out the type of the variable and it’s name. We do now not initialize it. But defining means declaration + initialization. E.G String s; is only a declaration while String s = new String (“abcd”); Or String s = “abcd”; are each definitions.

Question 23. Objects Are Passed By Value Or By Reference?

Answer :

Java most effective helps skip by way of fee. With gadgets, the item reference itself is handed via cost and so both the original reference and parameter reproduction each talk to the same object.

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Question 24. What Is Serialization?

Answer :

Serialization is a mechanism through which you can save the nation of an item by changing it to a byte circulate.

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Question 25. How Do I Serialize An Object To A File?

Answer :

The class whose instances are to be serialized need to enforce an interface Serializable. Then you bypass the instance to the Object Output Stream which is connected to a record output circulate. This will keep the item to a report.

Question 26. Which Methods Of Serializable Interface Should I Implement?

Answer :

The serializable interface is an empty interface; it does now not include any strategies. So, we do no longer implement any techniques.

Question 27. What Is The Common Usage Of Serialization?

Answer :

Whenever an object is to be sent over the network, objects need to be serialized. Moreover, if the kingdom of an item is to be saved, objects need to be serilazed.

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Question 28. What Is Externalizable Interface?

Answer :

Externalizable is an interface which includes  methods study External and write External. These strategies give you a manipulate over the serialization mechanism. Thus, in case your magnificence implements this interface, you may customise the serialization method by means of implementing those strategies.

Question 29. What One Should Take Care Of While Serializing The Object?

Answer :

One ought to make certain that each one the protected objects are also serializable. If any of the gadgets isn't always serializable then it throws a Not Serializable Exception.

Question 30. What Happens To The Static Fields Of A Class During Serialization?

Answer :

There are 3 exceptions in which serialization does no longer necessarily study and write to the circulation.

Serialization ignores static fields, because they're no longer part of any kingdom.
Base magnificence fields are most effective dealt with if the bottom class itself is serializable.
Transient fields.
Question 31. What Are The Different Ways To Handle Exceptions?

Answer :

There are two methods to address exceptions:

By wrapping the favored code in a strive block followed via a trap block to capture the exceptions.
List the preferred exceptions inside the throws clause of the technique and allow the caller of the method deal with those exceptions.
Question 32. What Is The Basic Difference Between The 2 Approaches To Exception Handling? 1> Try Catch Block And 2> Specifying The Candidate Exceptions In The Throws Clause? When Should You Use Which Approach?

Answer :

In the primary technique as a programmer of the method, you urself are coping with the exception. This is first-rate if you are in a high-quality role to determine should be completed in case of an exception. Whereas if it isn't always the duty of the technique to cope with its own exceptions, then do now not use this approach. In this case use the second one approach. In the second method, we are forcing the caller of the approach to capture the exceptions, that the technique is in all likelihood to throw. This is frequently the approach library creators use. They list the exception inside the throws clause and we ought to trap them. You will locate the equal approach all through the java libraries we use.

Question 33. What Is View Assembly ?

Answer :

A window defines the brilliant set of all viable perspectives that a Web Dynpro software ought to require at the same time as running a particular aspect. The variety of views visible at any one time but, will commonly be most effective a subset of the number of perspectives embedded in the window.

The subset of views rendered at any individual time is called the View Assembly. User interaction followed with the aid of next navigation processing will often reason this subset of views to alternate with each server round-trip. The view assembly represents the ones views seen via the consumer on their patron device after the finishing touch of a specific server spherical ride.

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Question 34. What Is Face Less Component ?

Answer :

It is a part with zero perspectives and zero windows. Such a element is called a “faceless” issue and is beneficial while a complex unit of functionality requiring no direct user interaction needs to be encapsulated. A excellent example of a faceless factor is the creation of some thing referred to as a version issue. This is not in reality a particular Web Dynpro component type; as a substitute it is a standard Web Dynpro thing that has been written specially for the challenge of interacting with a model object.

Question 35. What Are The Types Of Controller? Describe ?

Answer :

In huge terms, SAP has described  categories of Web Dynpro controller. The difference between them is absolutely this: A controller either

Has a visible interface, or

Does now not have a visible interface.

SAP has brought this difference with a view to maintain a strict separation among the ones components of the business utility that display facts (usually statistics customers), and people components of the business software that method data (generally facts mills).

Question 36. What Are Recursion Nodes ?

Answer :

The recursion node is a unique kind of node used while a node hierarchy with a recursive structure needs to be created. This is needed whilst, for example, the intensity of the node hierarchy is not recognised till runtime. Using a recursion node, you may claim that a particular node shape be replicated as a toddler of itself. A desirable instance right here is if your context needs to maintain facts in the identical structure as a document machine, containing directories and sub directories.

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Question 37. What Is An Empty View ?

Answer :

There is a special type of view known as the empty view. This view calls for no manual implementation, nor is it viable to have interaction with it in any manner other than invoking its default inbound plug – show Empty View. If you require one unique area of a view set to be empty, then you definitely need to embed the empty view into the view location. You can then deal with this view similar to every other view you've got written, besides that calling its inbound plug will motive the corresponding view vicinity to be blanked out. If a view set has had no views manually embedded into one in every of its view areas, then the empty view can be substituted mechanically.

Question 38. How Does The Web Dynpro Framework Decide Which Particular Views Make Up The Current View Assembly ?

Answer :

When an utility is accomplished for the first time, best those perspectives that have their default flag set to true will belong to the first view meeting.

Thereafter, user navigation will arise and the view assembly might be composed of these views which have been newly instantiated (as a consequence of their inbound plugs being fired), and people perspectives that persist from the previous view assembly (due to the fact no outbound navigation occurred from them).

Question 39. Define Webdynpro Controller?

Answer :

Controllers are the active parts of a Web Dynpro issue. In the layout of Web Dynpro controllers, SAP has made a large change to the original MVC idea of a controller.

Question 40. If The View Set Concept Is Not Implemented In Web Dynpro For Abap, What Options Are There For Reusing Views ?

Answer :

In both Web Dynpro for ABAP and Java, there's a particular UI Element called the View Container. This UI element, when brought to a view layout, acts as a box for any other view. View Containers can be organized in huge kind of methods in order to reap the favored format at the screen.

The perspectives that may be embedded into a View Container UI element are the subsequent:

Any view from the cutting-edge issue

Any visible interface from a infant Web Dynpro aspect

An empty view (supplied routinely by way of the Web Dynpro runtime)

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Question 41. What Is A View Set ?

Answer :

A view set is a visible framework that subdivides the window into predefined areas. Each subdivision of a view set is called a view place, and a couple of perspectives can be embedded right into a unmarried View Area.

The following preconfigured view sets are available:

T layout T format 90o T format 180o T format 270o Grid layout Tab strip

Each subdivision inside the view set layout is called a view place.

Question 42. How Is Model-pushed Architecture Implemented In Web Dynpro Framework ?

Answer :

Web dynpro framework uses declarative programming techniques to create a meta-version of the utility that is free from back-quit and front-cease programming languages. Rather the metadata is programming language-impartial and has information saved in XML format. It’s best at some stage in run-time that the rendering engine generates the code in html and java script from this meta version of the application. So the layout part – which defines the UI and information go with the flow among UI elements – is completely abstracted minimizing the coding (which is required best for implementing commercial enterprise common sense).

The version-driven method facilitates developer to attention much less on coding and technology part and greater at the layout part of the utility – “minimizing coding and maximizing layout”. Naturally, the primary focus of commercial enterprise software developer should be the business good judgment and the technological implementation ought to not distract him.

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Question forty three. How Can You Determine Lifespan Of Custom Controllers ?

Answer :

The lifespan of a custom controller is decided by way of a parameter setting made throughout the layout time assertion. It may be either “Framework Controlled” or “On demand”. If you pick out “Framework Controlled”, then the Web Dynpro framework will instantiate the custom controller when the aspect is instantiated. If but, you pick out “On demand”, then the Web Dynpro developer have to write the coding important to instantiate the custom controller.

Each baby thing utilization is instantiated with a unique call that ought to be described at design time. During the lifespan of the determine component, a child component might also simplest ever be instantiated once below a given name; but, need to it's vital, you can declare multiple usages of the same infant component as long as you specify distinctive utilization names.

Question forty four. Explain The Concept Of Lazy Data Access?

Answer :

The Web Dynpro framework has been constructed to observe the principle of Lazy Data Access. This means that the processing required to generate facts will not be invoked till the statistics is actually wished. When this precept is carried out to the architecture of the context, it means that unless there may be an try to access the information in a singleton baby node, then despite the fact that the lead selection within the figure node has changed, the kid node’s supply function will not be called.

Question forty five. Before A Mapping Relationship Can Be Established, What Criteria Must Be Met ?

Answer :

There need to be a suitable node to be had to act as a mapping origin