Top 5 Java Interview Questions on Object

This top 5 questions asked by most of the MNC during Java/J2ee interview . These questions are based on java object and its behavior. 


Q.1. How you can define an object ? How its related to real world and it behaves ? With Example.

Ans : This question is often asked for all java interview from 1-8 year experience candidate. As we know object is a real world entity. It has three basic property i.e. State, Behavior and Identity. Simply we can say its a blueprint of class. Any thing around you is called an object. But yes, it has the above three property by which we can define one object. 

State: what the objects have. Dog have a name, age, color,etc .It is implemented by variables in java.

Behavior: what the objects do.Dog can bark, bite, run, etc. It is implemented by methods in java.

Identity: what makes them unique, Dog have id-unique, which is unique. (this is important when implementing the equals method, to determine if the objects are different or not) . Every object has different hash code.

Example - Suppose , there are many dogs. But, you can't say , that is an object. You need to take one dog which has name - dick,age-8,color -white and it must have a unique identification. And now we can say dick is a dog object. And this dick can bark, bite and run. These are the behavior that object can do, and in its implemented by methods. 

Q.2. How many contructor & methods are in Object class ?

Ans: There are only one constructor and nine methods in Object class. Its available inside java.lang package.

Constructor :- 

public Object()

Methods :-

 clone() - This create and return copy of the same object.

 equals() - This is used to compare some other object is equal to this or not. 

 toString() - Convert and return a string representation.

 finalize() - This is called by garbage collector when there are no more active reference to that object exist.

 getClass() - This returns the runtime class of this object.

 hashCode() - Returns an hash code for this object and its unique.

 notify() - Wakes up a single thread that is waiting on this object's monitor.

 notifyAll() - Wakes up all thread that is waiting on this object's monitor.

 wait() - This will make object to wait , until any other thread notify this.

Q.3. Why wait() and notify() method is inside Object class instead of Thread class ?

 Ans : This is a FAQ for any java interview. Because, wait() and notify() method works with multi-threaded environment. This is inside Object class because, we are doing the monitoring work over an Object . When ever we are calling these methods , we are calling over object , not on thread.

Q.4. How many ways we can create object in Java ?

Ans : There are basic four way for creating object in java as below :-

By using new keyword -

Object obj=new Object();

By using class.forName() -

Dog dogObj=(Dog)class.forName("jdeveloperguide.lab.Dog").newtInstance();

By using deserialization -

ObjectInputStream inStream = new ObjectInputStream(anInputStream);
Dog dogObject = (Dog ) inStream.readObject();

By using clone() -

Dog dogObj=new Dog();
Dog dogObj2=dogObj.clone(); //It must implement clonnable interface.

Q.5. How JVM allocates object in memory ? What is heap and stack memory ?

Ans : Normally objects are allocated on heap memory. Heap memory is a dynamic memory which increase and decrease the size on run time. All primitive types,methods are allocated on stack memory. All object type and reference types are allocated on heap area.Every thread creates a stack (call stack ) and when thread completes the stack is also release the reserve memory. The stack is faster compare to heap.

You can share your interview experience with asked questions and answers for publishing on this blog.


All the Best for Interview !!!   




Find More Questions & Answers Below.

• Experience Java Interview  Questions & Answers. 
• Birla Soft Interview questions for Java 2-4 Year experience.
• Accenture Interview questions for Java  3-8 Year experience.
• Experienced Interview questions by Tavant Technologies.
• CGI Interview questions for Java 3-8 Year experience.
• Capgemini Java Interview questions for 3-8 Year experience. 
• IBM Java Interview questions for 3-8 Year Experience. 

Capgemini Interview Questions and Answers for Java 3-8 Year Experience

Experience Java/J2ee interview Questions asked by Capgemini.

1. Tell me about yourself ?

Ans : Give your brief introduction.

2. Explain about your current project?

Ans : It’s quite easy to describe your projects and your key role on this project. But, be careful and get ready about the functionality when you are describing your working module / part of the project. Show your confidence that you have done the major part and you can face challenges in future.

3. How many types of literals are there in JAVA ?

Ans : The literals means the value you are assigning to variable. You can specify the below types of literal in java.As per the primitive data types(int,short,long,float,double,boolean,char ,etc there is respective literal. Some literal needs to be ended with a specific character.Read More.

           long var=20L; //specify L or l for long literal

int var=20; // If not mentioned any character then its can be short or int

char var=’A’;

float var=10.44f; //specify f or F for float literal

double var=10.44;

boolean var=true; //or false

               

4. What is meant by Garbage collection ?

Ans :  Garbage collection is a automatic feature of java for cleaning the unused object from heap. It helps to developer for releasing the reserved memory without any extra effort by developer. It helps developer to save time and extra mental tension for handling object allocation in memory. When there is no reference to an object found, it will clean that object from memory . You can run the garbage collection explicitly by using System.gc() .    

5. Diffference between string s= new string (); and string s = "Hi Dude"; ?

Ans : Both statements are different to each other. Always ‘new’ keyword is used to create object.

String s=new String(); // This statement creates new object in heap. S is the object here.

String s=”Hi Dude” ; // This statement do not create object, its creating reference and its storing in String Constant Pool.S is the reference here.

6. What is singleton class? where is it used ?

Ans : View Answer

7. What is the difference between JSP and Servlets ?

Ans : As simple JSP is pre-compiled but Servlets are not. JSP is specially use for displaying/populating the data on browser. If we take an example of MVC architecture JSP plays the role of View (V). But, Servlets are used to handle the request and process the business logic. In MVC architecture Servlets are knows as Controller (C) .

8. What is the difference in using request.getRequestDispatcher() and context.getRequestDispatcher()?

Ans : Both are taking String parameter, but request.getRequestDispatcher() will dispatch the request inside the application. Where as context.getRequestDispatcher() will dispatch the request outside the context also. If you are using absolute path for dispatching then both are similar.

9. How the JSP file will be executed on the Server side ?

Ans : First its converted to java file. Then its compiled  by java compiler and creates the .class file.Now once you get the .class file you can execute it. Internally a JSP converts into respective servlet.

Conversion => Compilation => Execution

10. What is ActionServlet ?

Ans : ActionServlet provides the controller in struts application with MVC (Model-View-Controller) Model 2. 

ActionServlet is a sub class of javax.servlet.http.HttpServlet.It has few methods like

doGet(),doPost(),destroy(),etc.

11. What is Struts Validator Framework ?

Ans : Struts provides a convenient way to validate. Basically we are using two xml configuration file for configuring such as Validator.xml and validation-rule.xml . validation-rule.xml defines the rule of validation like number format validation,email validation. Apart from this ActionForm having validate() method which we can implement for validating the form data.

12. What is the difference between the Session and SessionFactory in hibernate ?

Ans : Session and SessionFactory are playing a prominent role in hibernate. SessionFactory is used to create Session  and its created once during starting of the application. You can have only one SessionFactory per application. SessionFactory is also called 2^ndlevel cache. But, Session could be many per application. Session is being created by using SessionFactory object.Session is called 1^st level cache.

13. What is HQL ? 

Ans : HQL stands for Hibernate Query Language. Its fully object oriented and quite similar with SQL.It supports association and joins for effective entity relationship.

All the Best for Interview !!!   



You can share your interview experience with asked questions and answers for publishing on this blog. 

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Find More Questions & Answers Below.

• Experience Java Interview  Questions & Answers. 
• Birla Soft Interview questions for Java 2-4 Year experience.
• Accenture Interview questions for Java  3-8 Year experience.
• Experienced Interview questions by Tavant Technologies.
• CGI Interview questions for Java 3-8 Year experience.
• Capgemini Java Interview questions for 3-8 Year experience. 
• IBM Java Interview questions for 3-8 Year Experience. 
• SapientNitro Interview questions for Java 2-6 Year experience.

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