Core Java Basic Interview Questions And Answers Pdf

31. What are the important benefits of using Hibernate Framework?
Answer:
Some of the important benefits of using hibernate framework are:
Hibernate eliminates all the boiler-plate code that comes with JDBC and takes care of managing resources, so we can focus on business logic.
Hibernate framework provides support for XML as well as JPA annotations, that makes our code implementation independent.
Hibernate provides a powerful query language (HQL) that is similar to SQL. However, HQL is fully object-oriented and understands concepts like inheritance, polymorphism, and association.
Hibernate is an open source project from Red Hat Community and used worldwide. This makes it a better choice than others because the learning curve is small and there are tons of online documentation and help is easily available in forums.
Hibernate is easy to integrate with other Java EE frameworks, it’s so popular that Spring Framework provides built-in support for integrating hibernate with Spring applications.
Hibernate supports lazy initialization using proxy objects and perform actual database queries only when it’s required.
Hibernate cache helps us in getting better performance.
For database vendor-specific feature, hibernate is suitable because we can also execute native sql queries.
Overall hibernate is the best choice in the current market for ORM tool, it contains all the features that you will ever need in an ORM tool.

32. What are the differences between getting and load method?
Answer:
The differences between getting () and load() methods are given below.
No. get() load()
1) Returns null if the object is not found. Throws ObjectNotFoundException if the object is not found.
2) get() method always hit the database. load() method doesn’t hit the database.
3) It returns a real object, not a proxy. It returns a proxy object.
4) It should be used if you are not sure about the existence of instance. It should be used if you are sure that the instance exists.

33. What are the advantages of Hibernate over JDBC?
Answer:
Some of the important advantages of Hibernate framework over JDBC are:
Hibernate removes a lot of boiler-plate code that comes with JDBC API, the code looks cleaner and readable.
Hibernate supports inheritance, associations, and collections. These features are not present with JDBC API.
Hibernate implicitly provides transaction management, in fact most of the queries can’t be executed outside transaction. In JDBC API, we need to write code for transaction management using commit and rollback.
JDBC API throws SQLException that is a checked exception, so we need to write a lot of try-catch block code. Most of the times it’s redundant in every JDBC call and used for transaction management. Hibernate wraps JDBC exceptions and throw JDBCException or HibernateException un-checked exception, so we don’t need to write code to handle it. Hibernate built-in transaction management removes the usage of try-catch blocks.
Hibernate Query Language (HQL) is more object oriented and close to java programming language. For JDBC, we need to write native sql queries.
Hibernate supports caching that is better for performance, JDBC queries are not cached hence performance is low.
Hibernate provide option through which we can create database tables too, for JDBC tables must exist in the database.
Hibernate configuration helps us in using JDBC like connection as well as JNDI DataSource for the connection pool.

This is a very important feature in enterprise application and completely missing in JDBC API.
Hibernate supports JPA annotations, so code is independent of the implementation and easily replaceable with other ORM tools. JDBC code is very tightly coupled with the application.
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34. What are the life-cycle methods for a jsp?
Answer:
Method Description
public void jspInit() It is invoked only once, same as init method of servlet.
public void _jspService(ServletRequest request,ServletResponse)throws ServletException,IOException It is invoked at each request, same as service() method of servlet.
public void jspDestroy() It is invoked only once, same as destroy() method of servlet.

35. What are the JSP implicit objects?
Answer:
JSP provides 9 implicit objects by default.

They are as follows:
Object Type
1) out JspWriter
2) request HttpServletRequest
3) response HttpServletResponse
4) config ServletConfig
5) session HttpSession
6) application ServletContext
7) pageContext PageContext
8) page Object
9) exception Throwable

36. What is the association?
Answer: Association is a relationship where all object have their own lifecycle and there is no owner. Let’s take the example of Teacher and Student. Multiple students can associate with a single teacher and a single student can associate with multiple teachers but there is no ownership between the objects and both have their own lifecycle. This relationship can be one to one, One to many, many to one and many to many.

37. What do you mean by aggregation?
Answer: an Aggregation is a specialized form of Association where all object have their own lifecycle but there is ownership and child object can not belong to another parent object. Let’s take an example of Department and teacher. A single teacher can not belong to multiple departments, but if we delete the department teacher object will not destroy.

38. What if the main() method is declared as private? What happens when the static modifier is removed from the signature of the main() method?
Answer: When the main() method is declared as private, the program compiles but during runtime it shows “main() method not public.” message.
When the static modifier is removed from the signature of the main() method, the Program compiles but at runtime throws an error “NoSuchMethodError”.

39.Can we rethrow the same exception from catch handler?
Answer: Yes we can rethrow the same exception from our catch handler. If we want to rethrow checked exception
from a catch block we need to declare that exception.

40. What is the first argument of the String array in main() method?
Answer: Unlike in C/C++ where the first element by default is the program name, the string array in main() has no element, the String array is empty.

41. What are the different ways of implementing thread? Which one is more advantageous?
Answer:
The thread can be implemented by
Using the runnable interface
Inheriting from the Thread class.
The use of the Runnable interface is more advantageous because when going for multiple inheritances, the only interface can help.

42. Why Java doesn’t support multiple inheritance ?
Answer: Java doesn’t support multiple inheritance in classes because of “Diamond Problem”. To know more about diamond problem with example, read Multiple Inheritance in Java.
However multiple inheritance is supported in interfaces. An interface can extend multiple interfaces because they just declare the methods and implementation will be present in the implementing class. So there is no issue of diamond problem with interfaces.

43. What are the differences between include directive and include action?
Answer:
include directive include action
The include directive includes the content at page translation time. They include action includes the content at request time.
The include directive includes the original content of the page so page size increases at runtime.

They include action doesn’t include the original content rather invokes the include() method of Vendor provided class.
It’s better for static pages. It’s better for dynamic pages.

44. What are the different tags provided in JSTL?
Answer:
There are 5 types of JSTL tags.
core tags
sql tags
xml tags
internationalization tags
functions tags

45. How to delete a Cookie in a JSP ?
Answer:
The following code explain how to delete a Cookie in a JSP:
Cookie mycook = new Cookie(“name1″,”value1”);
response.addCookie(mycook1);
Cookie killmycook = new Cookie(“mycook1″,”value1”);
killmycook . set MaxAge ( 0 );
killmycook . set Path (“/”);
killmycook . addCookie ( killmycook 1 );

46. Why should we not configure JSP standard tags in web.xml?
Answer: We don’t need to configure JSP standard tags in web.xml because when container loads the web application and find TLD files, it automatically configures them to be used directly in the application JSP pages. We just need to include it in the JSP page using taglib directive.
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47. For searches. Which one is most preferred: Array List or Linked List?
Answer:
ArrayList. Searching an element is faster in ArrayList compared to LinkedList.

48. What is the difference between Iterator and Enumeration ?
Answer:
1) Iterator allows removing elements from the underlying collection during the iteration using its remove() method. We cannot add/remove elements from a collection when using enumerator.
2) Iterator has improved method names.
Enumeration.hasMoreElement() -> Iterator.hasNext()
Enumeration.nextElement() -> Iterator.next().

49. What is the difference between Iterator and List Iterator?
Answer:
Following are the major differences between them:
1) Iterator can be used for traversing Set, List, and Map. ListIterator can only be used for traversing a List.
2) We can traverse only in the forward direction using Iterator. ListIterator can be used for traversing in both the directions(forward and backward).

50. Explain the jspDestroy() method?
Answer: jspDestry() method is invoked from javax.servlet.jsp.JspPage interface whenever a JSP page is about to be destroyed. Servlets destroy methods can be easily overridden to perform cleanup, like when closing a database connection.