How to check if an integer number is power of 2 in Java is one of the popular programming interview question and has been asked in many interviews. Surprisingly, this problem which looks simple enough to answer, doesn't turn out that simple if for many developers. Many Java programmers, both freshers and less experienced, struggle to write code for a function, which can check if number is power of 2 or not. There could be many different reasons for that, but it’s expected to at least come up with brute force solution. For those who are familiar with bitwise operators in Java , how positive and negative numbers are represented in binary format, this exercise is quite easy. Since negative numbers are represented as 2's complement value in Java, you can easily find if any number is power of 2 or not by looking at its bit pattern. Remember checking for power of two is different than checking if number is even or odd, that’s another thing to note. A number can be even, but it’s not necessary to be a power of two, e.g. 6 is even but it’s not a power of two.
Showing posts with label interview questions. Show all posts
Showing posts with label interview questions. Show all posts
Spring Hibernate JSTL foreach tag example in JSP - looping ArrayList
JSTL foreach loop in JSP
JSTL foreach tag is pretty useful while writing Java free JSP code. JSTL foreach tag allows you to iterate or loop Array List, HashSetor any other collection without using Java code. After introduction of JSTL and expression language(EL) it is possible to write dynamic JSP code without using scriptlet which clutters jsp pages. JSTL foreach tag is a replacement of for loop and behaves similarly like foreach loop of Java 5 but still has some elements and attribute which makes it hard for first-timers to grasp it. JSTL foreach loop can iterate over arrays, collections like List, Setand print values just like for loop. In this JSP tutorial we will see couple of example of foreach loop which makes it easy for new guys to understand and use foreach loop in JSP. By the way this is our second JSP tutorial on JSTL core library, in last tutorial we have seen How to use core <c:set> tag in JSP page.
Spring Hibernate How to delete empty files directories in Unix Linux
Deleting empty file and directory in Unix
Many times we need to find and delete empty files or directories in UNIX/Linux. Since there is no single command in Unix/Linux which allows you to remove empty files or empty directories rather we need to rely on find command and xargs command. In this UNIX and linux example we will see How to delete empty files and directories. Before removing empty files and directories we need to find those files and there are lots of option available to search for empty directories like find, grep, awk etc. You just need to know correct option. Like in any other operating system empty files and directories in Unix are those whose size is zero. Empty files doesn't contains any content while empty directories does not contain anything at all e.g files or sub-directories. As discussed in previous post 10 frequently used find command exampleswe can also use find command to search and delete empty files and directories as it provides searching files based on size as well.
Java J2EE Spring Top 10 Google Interview Questions Answers for Software Engineer - Books, Resources
These Google interview questions are some of my favorites collected from different sources. Every Programmer know that Google is one of the best technology company and its dream for many software developer to work for google, but at same time interview process at google is very tough and only few genuine intelligent programmers get through there interview process. Google interview questions are always been a good topic of discussion when few young software developer gathered around, I can still remember when one of my friend got call from google for interview then how whole bunch was got excited. We have searched a lot on internet on google interview questions and answers for him and us and then make a note of some of the best questions for preparation. I am listing down some google interview questions from that list. Apart from the popular questions asked in various Google Interview for software engineers or developers, books on algorithm and data structure plays a lot more important roles. Books like Algorithms for Interviews and Introduction to Algorithms are must read for any Programmer, who is serious about converting Google interview or similar companies like Facebook, Amazon and Microsoft. Once you start preparing for Google, rest of them become very easy.
Spring Framework How to find second highest or maximum salary of Employee in SQL - Interview question
How to find second highest or second maximum salary of an Employee is one of the most frequently asked SQL interview question similar to finding duplicate records in tableand when to use truncate vs delete. There are many ways to find second highest salary based upon which database you are using as different database provides different feature which can be used to find second maximum or Nth maximum salary of employee. Well this question can also be generalized with other scenario like finding second maximum age etc. In this SQL tutorial we will see different example of SELECT SQL query to find second highest salary independent of databases or you may call in ANSI SQL and other SQL queries which uses database specific feature to find second maximum salary.
Java J2EE Spring Core Java Interview Questions - Part 2
In the Previous part on Core Java Interview Questions, I had posted 50 questions. Since the post was getting too big, I left out some questions which are posted in this one.
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP Certification series) that cover these topics, which you might find useful. You can use them to revise/review your
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP Certification series) that cover these topics, which you might find useful. You can use them to revise/review your
Java J2EE Spring Core Java Interview Questions - Part 1
As part of the Java Interview Questions series, we have covered many large topics like Exception Handling, Threads, Garbage Collection etc. There are other topics of interest from an interview perpsective that are not large enough to warrant a seperate page. All those questions are collected here.
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP
Java J2EE Spring J2EE Interview Questions
The following are some questions you might encounter with respect to the J2EE Technology in any Interview for a Java J2EE Developer. The questions below are pretty exhaustive and practically speaking, you might not be asked most of the questions because - interviewers might prefer to test out your knowledge of core J2EE technologies like Servlets, JSPs, Struts, Hibernate etc. Nonetheless, there
Java J2EE Spring Java AWT Interview Questions
The following are some questions you might encounter with respect to the AWT components in any Interview. AWT stands for Abstract Window Toolkit and is used for creating UI components using Java. Though AWT is outdated and its successor Java Swings is more widely used, AWT is still being used by many projects.
Questions:
1. Which containers use a border Layout as their default layout?
The
Questions:
1. Which containers use a border Layout as their default layout?
The
Java J2EE Spring Java Classes & Interfaces Interview Questions
The following are some questions you might encounter with respect to Java Classes & Interfaces in any Java Interview. Classes and Interfaces are the building blocks of the Java Programming language and any experienced Java programmer needs to know the basics of Classes and Interfaces.
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP Certification
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP Certification
Java J2EE Spring Java Threads & Multi-threading Interview Questions
The following are some questions you might encounter with respect to Java Multi-threading in any Interview. Multi-threading is a powerful and rather a complicated feature of Java. Expertise in multithreading is an added advantage to any and every core java programmer.
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP Certification series) on Java
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP Certification series) on Java
Java J2EE Spring How to use truncate and delete command in SQL >> Tutorial and Example
Delete and truncate command in SQL
Truncate and delete in SQL are two commands which is used to remove or delete data from table. Though quite basic in nature both sql commands can create lot of trouble until you are familiar with details before using it. Truncate and delete are not just important to understand perspective but also a very popular interview topic which in my opinion a definite worthy topic. What makes them tricky is amount of data. Since most of Electronic trading system stores large amount of transactional data and some even maintain historical data, good understanding of delete and truncate command is required to effectively work on those environment.I have still seen people firing delete command just to empty a table with millions of records which eventually lock the whole table for doing anything and take ages to complete or Simply blew log segment or hang the machine.
Java J2EE Spring Java Garbage Collection Interview Questions
The following are some questions you might encounter with respect to Java Garbage collection in any Java Interview. Garbage Collection is a very important concept in the Java Programming Technology that helps clear out unused memory objects and keep the system running without any memory issues. Hence, a good knowledge of the Garbage collection processes is a mandatory skill for any core java
Java J2EE Spring Java Strings Interview Questions
The following are some questions you might encounter with respect to Strings in any Java Interview. Strings are very powerful and frankly speaking, there can be no Java based application that does not use Strings.
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP Certification series) on Strings that you might find useful. You can use them to
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP Certification series) on Strings that you might find useful. You can use them to
Java J2EE Spring Core Java Interview Questions - Objects
The following are some questions you might encounter with respect to Java Objects in any Java Interview. Everything in Java is an Object and the term Objects includes a lot of concepts. The questions below can be used to test a programmers understanding of the basic Object concepts in Java.
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP
Apart from the questions below, there are a few articles that I have put up (as part of the SCJP
Java J2EE Spring Core Java Interview Questions - Serialization
The following are some questions you might encounter with respect to Serialization in any Java Interview. Serialization is a powerful and useful concept that is widely used in many enterprise class Java Applications.
Apart from the questions below, there is an article that I have put up (as part of the SCJP Certification series) on Serialization that you might find useful. You can use it to
Apart from the questions below, there is an article that I have put up (as part of the SCJP Certification series) on Serialization that you might find useful. You can use it to
Java J2EE Spring Servlet Interview Questions
The following are some questions you might encounter with respect to Java Servlets in any Interview. Servlets are the back-bone of almost all J2EE Web Applications and any interviewer who is selecting people for his J2EE project would want a person who is confident & comfortable using them.
Apart from the questions below, there are a few articles that I have put up (as part of the SCWCD
Apart from the questions below, there are a few articles that I have put up (as part of the SCWCD
Java J2EE Spring JSP Interview Questions
The following are some questions you might encounter with respect to Java Server Pages or JSPs in any Interview. JSPs are an integral part of almost all J2EE Web Applications and any interviewer who is selecting people for his J2EE project would want a person who is confident & comfortable using them.
Apart from the questions below, there are a few articles that I have put up (as part of the
Apart from the questions below, there are a few articles that I have put up (as part of the
Java J2EE Spring HttpSession Interview Questions
The following are some questions you might encounter with respect to HttpSessions in any Interview. Sessions are a very powerful feature and any interviewer who is selecting people for his J2EE project would want a person who is confident & comfortable using them.
Apart from the questions below, there are a few articles that I have put up (as part of the SCWCD Certification series) on Sessions
Apart from the questions below, there are a few articles that I have put up (as part of the SCWCD Certification series) on Sessions
Java J2EE Spring Hibernate Interview Questions and Answers - 5
41) What is the difference between sorted and ordered collection in hibernate?
A) sorted collection vs. order collection
sorted collection :-
A sorted collection is sorting a collection by utilizing the sorting features provided by the Java collections framework. The sorting occurs in the memory of JVM which running Hibernate, after the data being read from database using java comparator.
If your collection is not large, it will be more efficient way to sort it.
order collection :-
Order collection is sorting a collection by specifying the order-by clause for sorting this collection when retrieval.
If your collection is very large, it will be more efficient way to sort it .
42) How will you configure Hibernate?
Answer:
The configuration files hibernate.cfg.xml (or hibernate.properties) and mapping files *.hbm.xml are used by the Configuration class to create (i.e. configure and bootstrap hibernate) the SessionFactory, which in turn creates the Session instances. Session instances are the primary interface for the persistence service.
" hibernate.cfg.xml (alternatively can use hibernate.properties): These two files are used to configure the hibernate sevice (connection driver class, connection URL, connection username, connection password, dialect etc). If both files are present in the classpath then hibernate.cfg.xml file overrides the settings found in the hibernate.properties file.
" Mapping files (*.hbm.xml): These files are used to map persistent objects to a relational database. It is the best practice to store each object in an individual mapping file (i.e mapping file per class) because storing large number of persistent classes into one mapping file can be difficult to manage and maintain. The naming convention is to use the same name as the persistent (POJO) class name. For example Account.class will have a mapping file named Account.hbm.xml. Alternatively hibernate annotations can be used as part of your persistent class code instead of the *.hbm.xml files.
43) What is a SessionFactory? Is it a thread-safe object?
Answer:
SessionFactory is Hibernate s concept of a single datastore and is threadsafe so that many threads can access it concurrently and request for sessions and immutable cache of compiled mappings for a single database. A SessionFactory is usually only built once at startup. SessionFactory should be wrapped in some kind of singleton so that it can be easily accessed in an application code.
SessionFactory sessionFactory = new Configuration().configure().buildSessionfactory();
44) What is a Session? Can you share a session object between different theads?
Answer:
Session is a light weight and a non-threadsafe object (No, you cannot share it between threads) that represents a single unit-of-work with the database. Sessions are opened by a SessionFactory and then are closed when all work is complete. Session is the primary interface for the persistence service. A session obtains a database connection lazily (i.e. only when required). To avoid creating too many sessions ThreadLocal class can be used as shown below to get the current session no matter how many times you make call to the currentSession() method.
&
public class HibernateUtil {
&
public static final ThreadLocal local = new ThreadLocal();
public static Session currentSession() throws HibernateException {
Session session = (Session) local.get();
//open a new session if this thread has no session
if(session == null) {
session = sessionFactory.openSession();
local.set(session);
}
return session;
}
}
It is also vital that you close your session after your unit of work completes. Note: Keep your Hibernate Session API handy.
45) What are the benefits of detached objects?
Answer:
Detached objects can be passed across layers all the way up to the presentation layer without having to use any DTOs (Data Transfer Objects). You can later on re-attach the detached objects to another session.
46) What are the pros and cons of detached objects?
Answer:
Pros:
" When long transactions are required due to user think-time, it is the best practice to break the long transaction up into two or more transactions. You can use detached objects from the first transaction to carry data all the way up to the presentation layer. These detached objects get modified outside a transaction and later on re-attached to a new transaction via another session.
Cons:
" In general, working with detached objects is quite cumbersome, and better to not clutter up the session with them if possible. It is better to discard them and re-fetch them on subsequent requests. This approach is not only more portable but also more efficient because - the objects hang around in Hibernate's cache anyway.
" Also from pure rich domain driven design perspective it is recommended to use DTOs (DataTransferObjects) and DOs (DomainObjects) to maintain the separation between Service and UI tiers.
47) How does Hibernate distinguish between transient (i.e. newly instantiated) and detached objects?
Answer:
" Hibernate uses the version property, if there is one.
" If not uses the identifier value. No identifier value means a new object. This does work only for Hibernate managed surrogate keys. Does not work for natural keys and assigned (i.e. not managed by Hibernate) surrogate keys.
" Write your own strategy with Interceptor.isUnsaved().
48) What is the difference between the session.update() method and the session.lock() method?
Both of these methods and saveOrUpdate() method are intended for reattaching a detached object. The session.lock() method simply reattaches the object to the session without checking or updating the database on the assumption that the database in sync with the detached object. It is the best practice to use either session.update(..) or session.saveOrUpdate(). Use session.lock() only if you are absolutely sure that the detached object is in sync with your detached object or if it does not matter because you will be overwriting all the columns that would have changed later on within the same transaction.
Note: When you reattach detached objects you need to make sure that the dependent objects are reatched as well.
49) How would you reatach detached objects to a session when the same object has already been loaded into the session?
You can use the session.merge() method call.
50) What are the general considerations or best practices for defining your Hibernate persistent classes?
1.You must have a default no-argument constructor for your persistent classes and there should be getXXX() (i.e accessor/getter) and setXXX( i.e. mutator/setter) methods for all your persistable instance variables.
2.You should implement the equals() and hashCode() methods based on your business key and it is important not to use the id field in your equals() and hashCode() definition if the id field is a surrogate key (i.e. Hibernate managed identifier). This is because the Hibernate only generates and sets the field when saving the object.
3. It is recommended to implement the Serializable interface. This is potentially useful if you want to migrate around a multi-processor cluster.
4.The persistent class should not be final because if it is final then lazy loading cannot be used by creating proxy objects.
5.Use XDoclet tags for generating your *.hbm.xml files or Annotations (JDK 1.5 onwards), which are less verbose than *.hbm.xml files.
51) What are Collection types in Hibernate?
? ArrayType,
Constructor: ArrayType(String role, String propertyRef, Class elementClass, boolean isEmbeddedInXML)
? BagType,
Constructor: BagType(String role, String propertyRef, boolean isEmbeddedInXML)
? CustomCollectionType, A custom type for mapping user-written classes that implement PersistentCollection
Constructor: CustomCollectionType(Class userTypeClass, String role, String foreignKeyPropertyName, boolean isEmbeddedInXML)
? IdentifierBagType,
Constructor: IdentifierBagType(String role, String propertyRef, boolean isEmbeddedInXML)
? ListType,
Constructor: ListType(String role, String propertyRef, boolean isEmbeddedInXML)
? MapType,
Constructor: MapType(String role, String propertyRef, boolean isEmbeddedInXML)
? SetType
Constructor: SetType(String role, String propertyRef, boolean isEmbeddedInXML)
Reference Books:
A) sorted collection vs. order collection
sorted collection :-
A sorted collection is sorting a collection by utilizing the sorting features provided by the Java collections framework. The sorting occurs in the memory of JVM which running Hibernate, after the data being read from database using java comparator.
If your collection is not large, it will be more efficient way to sort it.
order collection :-
Order collection is sorting a collection by specifying the order-by clause for sorting this collection when retrieval.
If your collection is very large, it will be more efficient way to sort it .
42) How will you configure Hibernate?
Answer:
The configuration files hibernate.cfg.xml (or hibernate.properties) and mapping files *.hbm.xml are used by the Configuration class to create (i.e. configure and bootstrap hibernate) the SessionFactory, which in turn creates the Session instances. Session instances are the primary interface for the persistence service.
" hibernate.cfg.xml (alternatively can use hibernate.properties): These two files are used to configure the hibernate sevice (connection driver class, connection URL, connection username, connection password, dialect etc). If both files are present in the classpath then hibernate.cfg.xml file overrides the settings found in the hibernate.properties file.
" Mapping files (*.hbm.xml): These files are used to map persistent objects to a relational database. It is the best practice to store each object in an individual mapping file (i.e mapping file per class) because storing large number of persistent classes into one mapping file can be difficult to manage and maintain. The naming convention is to use the same name as the persistent (POJO) class name. For example Account.class will have a mapping file named Account.hbm.xml. Alternatively hibernate annotations can be used as part of your persistent class code instead of the *.hbm.xml files.
43) What is a SessionFactory? Is it a thread-safe object?
Answer:
SessionFactory is Hibernate s concept of a single datastore and is threadsafe so that many threads can access it concurrently and request for sessions and immutable cache of compiled mappings for a single database. A SessionFactory is usually only built once at startup. SessionFactory should be wrapped in some kind of singleton so that it can be easily accessed in an application code.
SessionFactory sessionFactory = new Configuration().configure().buildSessionfactory();
44) What is a Session? Can you share a session object between different theads?
Answer:
Session is a light weight and a non-threadsafe object (No, you cannot share it between threads) that represents a single unit-of-work with the database. Sessions are opened by a SessionFactory and then are closed when all work is complete. Session is the primary interface for the persistence service. A session obtains a database connection lazily (i.e. only when required). To avoid creating too many sessions ThreadLocal class can be used as shown below to get the current session no matter how many times you make call to the currentSession() method.
&
public class HibernateUtil {
&
public static final ThreadLocal local = new ThreadLocal();
public static Session currentSession() throws HibernateException {
Session session = (Session) local.get();
//open a new session if this thread has no session
if(session == null) {
session = sessionFactory.openSession();
local.set(session);
}
return session;
}
}
It is also vital that you close your session after your unit of work completes. Note: Keep your Hibernate Session API handy.
45) What are the benefits of detached objects?
Answer:
Detached objects can be passed across layers all the way up to the presentation layer without having to use any DTOs (Data Transfer Objects). You can later on re-attach the detached objects to another session.
46) What are the pros and cons of detached objects?
Answer:
Pros:
" When long transactions are required due to user think-time, it is the best practice to break the long transaction up into two or more transactions. You can use detached objects from the first transaction to carry data all the way up to the presentation layer. These detached objects get modified outside a transaction and later on re-attached to a new transaction via another session.
Cons:
" In general, working with detached objects is quite cumbersome, and better to not clutter up the session with them if possible. It is better to discard them and re-fetch them on subsequent requests. This approach is not only more portable but also more efficient because - the objects hang around in Hibernate's cache anyway.
" Also from pure rich domain driven design perspective it is recommended to use DTOs (DataTransferObjects) and DOs (DomainObjects) to maintain the separation between Service and UI tiers.
47) How does Hibernate distinguish between transient (i.e. newly instantiated) and detached objects?
Answer:
" Hibernate uses the version property, if there is one.
" If not uses the identifier value. No identifier value means a new object. This does work only for Hibernate managed surrogate keys. Does not work for natural keys and assigned (i.e. not managed by Hibernate) surrogate keys.
" Write your own strategy with Interceptor.isUnsaved().
48) What is the difference between the session.update() method and the session.lock() method?
Both of these methods and saveOrUpdate() method are intended for reattaching a detached object. The session.lock() method simply reattaches the object to the session without checking or updating the database on the assumption that the database in sync with the detached object. It is the best practice to use either session.update(..) or session.saveOrUpdate(). Use session.lock() only if you are absolutely sure that the detached object is in sync with your detached object or if it does not matter because you will be overwriting all the columns that would have changed later on within the same transaction.
Note: When you reattach detached objects you need to make sure that the dependent objects are reatched as well.
49) How would you reatach detached objects to a session when the same object has already been loaded into the session?
You can use the session.merge() method call.
50) What are the general considerations or best practices for defining your Hibernate persistent classes?
1.You must have a default no-argument constructor for your persistent classes and there should be getXXX() (i.e accessor/getter) and setXXX( i.e. mutator/setter) methods for all your persistable instance variables.
2.You should implement the equals() and hashCode() methods based on your business key and it is important not to use the id field in your equals() and hashCode() definition if the id field is a surrogate key (i.e. Hibernate managed identifier). This is because the Hibernate only generates and sets the field when saving the object.
3. It is recommended to implement the Serializable interface. This is potentially useful if you want to migrate around a multi-processor cluster.
4.The persistent class should not be final because if it is final then lazy loading cannot be used by creating proxy objects.
5.Use XDoclet tags for generating your *.hbm.xml files or Annotations (JDK 1.5 onwards), which are less verbose than *.hbm.xml files.
51) What are Collection types in Hibernate?
? ArrayType,
Constructor: ArrayType(String role, String propertyRef, Class elementClass, boolean isEmbeddedInXML)
? BagType,
Constructor: BagType(String role, String propertyRef, boolean isEmbeddedInXML)
? CustomCollectionType, A custom type for mapping user-written classes that implement PersistentCollection
Constructor: CustomCollectionType(Class userTypeClass, String role, String foreignKeyPropertyName, boolean isEmbeddedInXML)
? IdentifierBagType,
Constructor: IdentifierBagType(String role, String propertyRef, boolean isEmbeddedInXML)
? ListType,
Constructor: ListType(String role, String propertyRef, boolean isEmbeddedInXML)
? MapType,
Constructor: MapType(String role, String propertyRef, boolean isEmbeddedInXML)
? SetType
Constructor: SetType(String role, String propertyRef, boolean isEmbeddedInXML)
Reference Books:
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