These are some interview question and answer asked during my recent interview. Oracle interview questions are very important during any programming job interview. Interviewer always want to check how comfortable we are with any database either we go for Java developer position or C, C++ programmer position .So here I have discussed some basic question related with oracle database. Apart from these questions which is very specific to Oracle database you may find some general questions related to database fundamentals and SQL e.g. Difference between correlated and noncorrelated subquery in database or truncate vs delete in SQL etc.
Sunday, December 31, 2017
Top 10 Oracle Interview Question and Answer - Database and SQL
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Saturday, December 30, 2017
Step By Step guide to Read XML file in Java Using SAX Parser Example
Reading XML file in java using SAX Parser is little different than reading xml file in Java with DOM parser which we had discussed in last article of this series. This tutorial is can be useful for those who are new to the java world and got the requirement for read an xml file in java in their project or assignment, key feature of java is it provides built in class and object to handle everything which makes our task very easy. Basically this process of handling XML file is known as parsing means break down the whole string into small pieces using the special tokens.
Parsing can be done using two ways:
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core java
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Java xml tutorial
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xml
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java.lang.UnsupportedClassVersionError: Bad version number in .class files Cause and Solution
How to fix Bad version number in .class file
"java.lang.UnsupportedClassVersionError: Bad version number in .class file" is a common error in Java programming language which comes when you try to run a Java class file. In our last article, we discussed that how to resolve Java.lang.UnSupportedClassVersionError and found that it comes when a major and minor version of the class is not supported by Java virtual machine or JRE running the program. Though "java.lang.UnsupportedClassVersionError: Bad version number in .class file" is little different than that of its manifestation and Cause.
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core java
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error and exception
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Difference between DOM and SAX Parsers in Java
A difference between SAX and DOM Parser is very popular Java interview and often asked when interviewed on Java and XML. Both DOM and SAX parser are extensively used to read and parse XML file in java and have their own set of advantage and disadvantage which we will cover in this article. Though there is another way of reading XML file using XPath in Java which is the more selective approach like SQL statements people tend to stick with XML parsers. DOM Parser vs SAX parsers is also often viewed in terms of speed, memory consumption and their ability to process large XML files.
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core java
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core java interview question
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Java xml tutorial
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How to read and write Images in java using ImageIO Utility
Writing an Image file in Java is very common scenario and in this article we will see a new way to write images into file in Java. javax.imageio.ImageIO is a utility class which provides lots of utility method related to images processing in Java. Most common of them is reading form image file and writing images to file in java. You can write any of .jpg, .png, .bmp or .gif images to file in Java. Just like writing, reading is also seamless with ImageIO and you can read BufferedImage directly from URL.
How to Convert a Map to a List in Java Example
Map and List are two common data structures available in Java and in this article we will see how can we convert Map values or Map keys into List in Java. The primary difference between Map (HashMap, ConcurrentHashMap or TreeMap) and List is that Map holds two objects key and value while List just holds one object which itself is a value. Key in hashmap is just an addon to find values, so you can just pick the values from Map and create a List out of it. The map in Java allows duplicate value which is fine with List which also allows duplicates but Map doesn't allow duplicate key.
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core java
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java collection tutorial
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How to Compare Arrays in Java – Equals vs deepEquals Example
java.util.Arrays class provides equals() and deepEquals() method to compare two Arrays in Java. Both of these are overloaded method to compare primitive arrays e.g. int, long, float, double and Object arrays e.g. Arrays.equals(Object[] , Object[]). Arrays.equals() returns true if both Arrays which it is comparing are null If both arrays pointing to same Array Object or they must be of the same length and contains the same element in each index. In all other cases, it returns false. Arrays.equals() calls equals() method of each Object while comparing Object arrays.
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Friday, December 29, 2017
How to append text into File in Java – FileWriter Example
Some times we need to append text into File in Java instead of creating
new File. Thankfully Java File API is very rich and it provides several ways to
append text into File in Java. Previously we have seen how
to create file and directory in Java and how
to read and write to text file in Java and in this Java IO tutorial we will
see how to append text into file in Java. We are going to use standard FileWriter and BufferedWriter approach
to append text to File. One of the key point to remember while using FileWriter in Java is
to initialize FileWriter to append text i.e. writing bytes
at the end of File rather than writing on beginning of the File.
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core java
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java IO tutorial
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programming
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4 example to Iterate over HashMap, Hashtable or any Map in Java
There are multiple ways to iterate, traverse or loop through Map, HashMap or TreeMap in Java and we all familiar of either all of those or some of those. But to my surprise, one of my friends was asked in his interview (he has more than 6 years of experience in Java programming) to write code for getting values from hashmap or TreeMap in Java with at least 4 ways. Just like me he also surprised on this question but written it. I don't know why exactly someone asks this kind of java interview question to a relatively senior java programmer. Though my closest guess is to verify that whether he is still hands on with coding in java. Anyway, that gives me an idea to write this Java tutorial and here are multiple ways to traverse, iterate or loop on a Map in Java, so remember this because you may also ask this question J.
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core java
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HashMap
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java collection tutorial
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Difference between equals method and "==" operator in Java - Interview Question
Both equals() and "==" operator in Java is used to compare objects to check equality but the main difference between equals method and the == operator is that former is a method and later is an operator. Since Java doesn’t support operator overloading, == behaves identical for every object but equals() is method, which can be overridden in Java and logic to compare objects can be changed based upon business rules. Another notable difference between == and equals method is that former is used to compare both primitive and objects while later is only used for objects comparison.
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core java
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core java interview question
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programming
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What is final in Java? Final variable , Method and Class Example
Final in Java is very important keyword and can be applied to class, method, and variables in Java. In this java final tutorial we will see what is a final keyword in Java, what does it mean by making final variable, final method and final class in java and what are primary benefits of using final keywords in Java and finally some examples of final in Java. Final is often used along with static keyword in Java to make static final constant and you will see how final in Java can increase the performance of Java application.
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final modifier
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How to add, subtract days, months, years, hours from Date and Time in Java
Adding days, hours, month or years to dates is a common task in Java. java.util.Calendar can be
used to perform Date and Time arithmetic in Java. Calendar class not only
provides date manipulation but it also support time manipulation i.e. you can
add, subtract hours, minutes and seconds from current time. Calendar class
automatically handles date transition or month transition for example if you
ask date after 30 days it will return you date based on whether current month
is 30 or 31 days long. Same is true in case of adding and subtracting years,
Calendar takes care whether current or following year is a leap
year or not.
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core java
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date and time tutorial
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programming
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Difference between Primary key vs Foreign key in table – SQL database tutorial
The main difference between Primary key and Foreign key in a table is that it’s the same column which behaves as primary key in the parent table and as a foreign key in a child table. For example in Customer and Order relationship, customer_id is the primary key in Customer table but a foreign key in Order table. By the way, what is a foreign key in a table and difference between Primary and Foreign key are some of the popular SQL interview questions, much like truncate vs delete in SQL or difference between correlated and noncorrelated subquery?
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database
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database interview questions
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mysql
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SQL
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SQL Interview Questions
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Sybase and SQL Server
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Thursday, December 28, 2017
How to fix java.lang.classcastexception cannot be cast to in Java - cause and solution
As name suggests ClassCastException in Java
comes when we try to type cast an object and object is not of the type we are
trying to cast into. In fact ClassCastException in Java is
one of most common exception in Java along with java.lang.OutOfMemoryError
and ClassNotFoundException
in Java before Generics was introduced in Java 5 to avoid frequent
instances of java.lang.classcastexception cannot be cast to while
working with Collection classes like ArrayList
and HashMap,
which were not type-safe before Java 5. Though we can minimize and avoid java.lang.ClassCastException in Java by
using Generics and writing type-safe
parameterized classes and method, its good to know real cause of ClassCastException and How to
solve it.
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core java
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error and exception
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programming
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Difference between Class and Object in Java and OOPS with Example
Class and Object are two most important concept of Object oriented
programming language (OOPS) e.g. Java. Main
difference between a Class and an Object in Java is that class
is a blueprint to create different objects of same type. This may looks
simple to many of you but if you are beginner or just heard term Object
Oriented Programming language it might not be that simple. I have met many
students, beginners and programmers who don’t know difference between class and
object and often used them interchangeably. Also Java API having classes like java.lang.Object and java.lang.Class also adds more
confusion in beginners' mind. Both of them are totally different things, class
and object in OOPS are concepts and applicable to all Object-oriented
programming language e.g. C++ or Scala.
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object oriented programming
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The real difference between Process and Thread in Java
One of the common questions from programming interviews is, what is the difference between a Thread and a Process? Well, the main difference between them is that a Process is a program that is executing some code and a thread is an independent path of execution in the process. A process can have more than one thread for doing independent task e.g. a thread for reading data from disk, a thread for processing that data, and another thread for sending that data over the network. This technique to improve throughput and better utilize CPU power is also known as multi-threading.
How to Attach Source Code in Eclipse to JAR Files for Debugging and Navigation With JDK Example
Attaching the source of any Jar in Eclipse e.g. JDK or open-source libraries like Spring framework is a good idea because it helps during debugging and code development. As a Java programmer at least you should attach the source of JDK in Eclipse IDE to find out more about JDK classes. Though Eclipse IDE is pretty good on code assist, sometimes You want to know what's going inside a library or a JDK method, rather than just reading the documentation. Interview questions like How HashMap works in Java or How substring cause memory leak can only be answered if you are familiar with the source code of these classes.
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Eclipse
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How to Parse or Read XML File in Java >> XML Tutorial Example
How to parse xml file in Java or how to read xml file in java is one of common need of a Java Developer working with enterprise Java application which uses XML for data representation, messaging and data transfer. Java has good support to handle XML files and XML Documents and you can read XML File in Java, create or write to XML file in Java by using various XML parsers available. Reading XML file is little bit different than reading text or binary file in Java but it uses same concept of File class.
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core java
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Java xml tutorial
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xml
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Wednesday, December 27, 2017
Recursion in Java With Example – Programming Techniques Tutorial
Recursion is one of the tough programming techniques to master. Many programmers working on both Java and other programming languages like C or C++ struggles to think recursively and figure out the recursive pattern in the problem statement, which makes it is one of the favorite topics of any programming interview. If you are new in Java or just started learning Java programming language and you are looking for some exercise to learn the concept of recursion than this tutorial is for you. In this programming tutorial, we will see a couple of examples of recursion in Java programs and some programming exercise which will help you to write recursive code in Java-like calculating Factorial, reversing String and printing Fibonacci series using recursion technique.
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coding
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core java
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data structure and algorithm
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programming
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What is Referential Integrity in Database or SQL - MySQL Example Tutorial
Referential Integrity is set of constraints applied to foreign key which
prevents entering a row in child table (where you have foreign key) for which
you don't have any corresponding row in parent table i.e. entering NULL or
invalid foreign keys. Referential
Integrity prevents your table from having
incorrect or incomplete relationship e.g. If you have two tables Order and Customer where Customer is parent
table with primary
key customer_id and Order is child
table with foreign key customer_id. Since as per business rules you
can not have an Order without a Customer and this
business rule can be implemented using referential
integrity in SQL on relational database.
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database
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database interview questions
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mysql
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SQL
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SQL Interview Questions
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How to create thread safe Singleton in Java - Java Singleton Example
Thread safe Singleton means a Singleton class which returns exactly same instance even if exposed to multiple threads. Singleton in Java has been a classical design pattern like Factory method pattern or Decorator design pattern and has been used a lot even inside JDK like java.lang.Runtime is an example of Singleton class. Singleton pattern ensures that exactly one instance of class will remain in Java program at any time. In our last post 10 Interview questions on Singleton in Java we have discussed many different questions asked on Singleton pattern, One of them was writing Thread safe singleton in Java.
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How to convert milliseconds to Date in Java - tutorial example
Do you want to convert milliseconds to Date in Java ? Actually java.util.Date is internally
specified in milliseconds from epoch. So any date is number of millisecond
passed since January 1, 1970, 00:00:00 GMT and Date provides constructor
which can be used to create Date from
milliseconds. Knowing the fact that Date is internally maintained in
milliseconds allows you to store date in form of millisecond in Server or in
your Class
because that can be effectively expressed with a long
value.
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core java
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date and time tutorial
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programming
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3 Examples to Print Array Elements/Values in Java - toString and deepToString from Arrays
Printing array values in Java or values of an array element in Java would
have been much easier if arrays are
allowed to directly prints its values whenever used inside System.out.println() or format
and printf method, Similar to various classes in Java do this by overriding
toString() method. Despite being an object, array in Java doesn't print any
meaningful representation of its content when passed to System.out.println() or any
other print methods. If you are using array in method argument or any other a prominent place in code and actually interested in values of an array then you
don't have much choice than for loop until Java 1.4.
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java 5 tutorial
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Tuesday, December 26, 2017
How to check if a number is a palindrome or not in Java - Example
How to check if a number is a palindrome or not is a variant of popular String
interview question how to check if a String is a palindrome or not. A number
is said to be a palindrome if the number itself is equal to reverse of number e.g.
313 is a palindrome because the reverse of this number is also 313. On the other
hand 123 is not a palindrome because the reverse of 123 is 321 which is not equal
to 123, i.e. original number. In order to check if a number is a palindrome or
not we can reuse the logic of How
to reverse a number in Java.
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Inner class and nested Static Class in Java with Example
Inner class and nested static class in Java both are classes declared inside another class, known as top level class in Java. In Java terminology, If you declare a nested class static, it will called nested static class in Java while non static nested class are simply referred as Inner Class. Inner classes are also a popular topic in Java interviews. One of the popular questions is the difference between inner class and nested static class , some time also refereed as difference between static and non static nested class in Java. One of the most important question related to nested classes are Where should you use nested class in Java?
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core java interview question
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How to Add, Modify and Drop Column With Default Value, NOT NULL Constraint – MySQL Database Example
How to add column in existing table with default value is another popular
SQL
interview question asked for Junior level programming
job interviews. Though syntax of SQL query to add column with default value
varies little bit from database to database, it always been performed using
ALTER keyword of ANSI SQL. Adding column in existing table in MySQL database
is rather easy and straight forward and we will see example of SQL query for MySQL database which adds a column with default value. You can also provide
constraints like NULL or NOT NULL while
adding new column in table.
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database
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database interview questions
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mysql
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SQL
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SQL Interview Questions
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Sybase and SQL Server
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Checked vs Unchecked Exception in Java Example
Checked and Unchecked Exception is two types of Exception exist in Java. Though there is no difference in functionality and you can very achieve same thing with either checked Exception or Unchecked Exception, there is some difference on exception handling part. In this Java tutorial we will see what is checked and Unchecked Exception in Java, Examples of Checked and Unchecked Exception and most importantly we will learn when to use Checked Exception and when to use Unchecked Exception in Java and lastly we will see difference between checked and unchecked exception to understand things better. By the way this article is second in my post on Exception along with difference between throw and throws in Java and improved Exception handling in Java 7 with Automatic resource management ARM and multi-catch block in JDK 7.
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core java interview question
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error and exception
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What is Type Casting in Java - Casting one Class to other class or interface Example
Type casting in Java is to cast one type, a class or interface, into another type i.e. another class or interface. Since Java is an Object oriented programming language and supports both Inheritance and Polymorphism, It’s easy that Super class reference variable is pointing to SubClass object but the catch here is that there is no way for Java compiler to know that a Superclass variable is pointing to SubClass object. Which means you can not call a method which is declared in the subclass. In order to do that, you first need to cast the Object back into its original type. This is called type casting in Java. You can type cast both primitive and reference type in Java. The concept of casting will be clearer when you will see an example of type casting in next section.
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coding
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core java
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object oriented programming
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Monday, December 25, 2017
How to Create Auto Incremented Identity Column in SQL Server, MySQL, Sybase and Oracle?
Automatic incremented ID, Sequence or Identity columns are those columns
in any table whose value is automatically incremented by database based upon
predefined rule. Almost all databases e.g. Microsoft
SQL Server, MySQL,
Oracle
or Sybase supports auto-incremented identity columns but in different ways like
Oracle provides a SEQUENCE object which can be used to
generate automatic numbers, Microsoft SQL Server up to 2008 version provides IDENTITY() functions
for a similar purpose. Sybase also has IDENTITY function
but little different than SQL Server and MySQL uses auto_incremented keyword to
make any numeric column auto-incremented.
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database
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database interview questions
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mysql
,
SQL
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SQL Interview Questions
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Sybase and SQL Server
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Observer design Pattern in Java with Real world code Example
Observer design pattern in Java is a fundamental core Java pattern where Observe watch for any change in state or property of Subject. For Example Company updates all its shareholders for any decision they make here Company is Subject and Shareholders are Observers, any change in policy of company and Company notifies all its Shareholders or Observer. This was simple real world explanation of Observer pattern. In this article we will in detail what is Observer Design pattern, what is benefit of Observer design Pattern, Example or Observer pattern in Java and few other points. Just like Decorator design Pattern and Factory Pattern in Java, Observer pattern is also used in JDK.
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design patterns
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object oriented programming
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How to Parse or Convert String to long in Java - 4 Examples
How to convert a string to long in Java is one of those frequently asked questions by a beginner who has started learning Java programming language and not aware of how to convert from one data type to another. Converting String to long is similar to converting String to Integer in Java, in-fact if you know how to convert String to Integer than you can convert String to Long by following the same procedure. Though you need to remember few things while dealing with long and String first of all long is the primitive type which is wrapped by Long wrapper class and String is an Object in Java backed by character array.
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Coding Interview Question
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core java
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programming
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How to fix java.io.NotSerializableException: org.apache.log4j.Logger Error in Java
java.io.NotSerializableException:
org.apache.log4j.Logger error says that an instance of org.apache.lo4j.Logger is not
Serializable. This error comes when we use log4j for logging
in Java and create Logger in a Serializable class e.g. any domain class or
POJO which we want to store in HttpSession or want to
serialize it. As we know from 10
Java Serialization interview question that, if you have a non serializable
class as member in a Serializable class, it will throw java.io.NotSerializableException Exception.
Look at the below code :
public class Customer implements Serializable{
private Logger logger = Logger.getLogger(Customer.class)
......
}
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debugging
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error and exception
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How to redirect a page or URL using JavaScript and JQuery
Redirecting a web page means, taking the user to a new location. Many website uses redirects for many different reasons, e.g. Some websites redirect users from the old domain to new domain, some redirect from one page to another e.g. a more relevant page. If you are a Java programmer and worked previously with Servlet and JSP, then you might be familiar with SendRedirect and Forward methods, which are used to redirect users in web applications. Actually, there are two kinds of redirect, Server side redirect, and client-side redirect. In Server side redirect, server initiates redirection, while in a client-side redirect, client code does the redirection. Redirecting a web page using JavaScript and JQuery is a client-side redirection.
How to change Tomcat default port 8080
Tomcat default port is 8080 but many times other Java application also uses 8080 like any other web-server Resin or Jetty and starting tomcat may result in java.net.BindException:Address already in use: JVM_Bind 8080. In order to avoid this exception you can change default port of tomcat from 8080 to some other port e.g. 8081 or 8082. Though don't change to tomcat port which is likely to be used by tomcat itself e.g. 8443 is used by tomcat https port. Use port which is most likely to be free. In this tomcat tutorial we will see how to change default port 8080 for http protocol in tomcat and port 8443 port for https protocol in tomcat.
How to Create and Evaluate XPath Expression in Java - Tutorial and Example
You can use XPathExpression from javax.xml.xpath package to create and
execute XPATH expression in Java. Java
API provides javax.xml.xpath package, which contains classes like Xpath, XpathFactory to work
with XPATH and XML documents. By the way this is third article on Xpath, In
last couple of tutorials e.g. XPATH examples to select values using
attributes and my XPATH notes for Java programmer,
we have seen basics of Xpath expression from XML and Java point of view. Anyone who has work with XML technologies in
Java knows importance of XPATH, it is one the most useful technology to
retrieve selected data from XML files.
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Java xml tutorial
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programming
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xml
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Sunday, December 24, 2017
VirtualBox - /sbin/mount.vboxsf: mounting failed with the error: Protocol error [Solution]
I use Oracle's virtual machine, Virtualbox to run the Linux operating system from my Windows machine. It's the most simple way to have two operating system in your laptop or PC. Since I run most of Java program in Linux, VirtualBox gives me a nice interface to run UNIX commands right from Windows box. This blog post is about the mounting of shared folder failed error in Oracle's Virtualbox VM. It was working fine day before yesterday and now, after I restarted my virtual box and tried to mount my shared folder, I was greeted by this error: "/sbin/mount.vboxsf: mounting failed with the error: Protocol error". I was using the following command to mount my shared folder on VirtualBox:
I was running Oracle's VirtualBox 4.1 version with the guest operating system as RedHat Linux and host OS as Windows 8.
$ mount -t vboxsf mountfolder /home/devInHost/mountfolder
I was running Oracle's VirtualBox 4.1 version with the guest operating system as RedHat Linux and host OS as Windows 8.
How to Split String in SQL Server and Sybase
Sometimes we need to split a long comma-separated String in Stored
procedure e.g. Sybase or SQL Server
stored procedures. It's quite common to pass comma
delimited or delimiter separated String as an input parameter to Stored
procedure and then later split comma separated String into multiple values
inside stored proc. This is not just the case of the input parameter but you can also
have a comma-separated string in any table data. Unfortunately, there is no split() function
in Sybase or SQL Server 2005 or 2008 which can directly split a string based on
delimiter just like in Java
string split method. Fortunately, Sybase Adaptive Server and Microsoft SQL
server has functions like CHARINDEX and PATINDEX which can
be used to split comma separated String.
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database
,
database interview questions
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SQL
,
SQL Interview Questions
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Sybase and SQL Server
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How to get current date, month, year and day of week in Java program
Here is quick Java tip to get the current date, month, year, and day of week
from Java program. Java provides a rich Date and Time API though having thread-safety
issue but its rich in function and if used locally can give you all the
date and time information which you need for your enterprise Java application. In
last Java tutorial on Date and Time API we have seen how
to get current date and time from different timezone using DateFormat and SimpleDateFormat classes
and in this post, we will get some more details like a current month, year, day of the week, etc by using java.util.Calendar class. Just keep in mind that the Calendar instance should
not be shared between multiple threads.
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coding
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core java
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date and time tutorial
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programming
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How to Create and Modify Properties File Form Java Program in Text and XML Format
Though most of the time we create and modify properties file using text
editor like notepad, word-pad or edit-plus, It’s also possible to create and edit
properties file from Java program. Log4j.properties, which is
used to configure Log4J based logging
in Java and jdbc.properties which is used to specify configuration
parameters for database
connectivity using JDBC are two most common example of property file in
Java. Though I have not found any real situation where I need to create
properties file using Java program but it’s always good to know about
facilities available in Java API. In last Java tutorial on Properties we have
seen how
to read values from properties file on both text and XML format and in this the article we will see how to create properties file on both text and XML format.
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coding
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core java
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Java xml tutorial
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programming
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How to Count Occurrences of a Character in String - Java Programming Exercise Example
Write a program to count the number of occurrences of a character in String is one of the common programming interview questions not just in Java but also in other programming languages like C or C++. As String in a very popular topic on programming interviews and there are a lot of good programming exercise on String like "count number of vowels or consonants in String", "count number of characters in String", How to reverse String in Java using recursion or without using StringBuffer, etc, it becomes extremely important to have a solid knowledge of String in Java or any other programming language. Though, this question is mostly used to test the candidate's coding ability i.e. whether he can convert logic to code or not.
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coding
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Coding Interview Question
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core java
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core java interview question
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How to read input from command line in Java using Scanner
Java 5 introduced a nice utility called java.util.Scanner is capable of reading input from the command line in Java. Using Scanner is a nice and clean way of retrieving user input from console or command line. The scanner can accept InputStream, Reader or simply path of the file from where to read input. In order to read from the command line, we can pass System.in into Scanner's constructor as a source of input. The scanner offers several benefits over the classical BufferedReader approach, here are some of the benefits of using java.util.Scanner for reading input from the command line in Java:
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core java
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homework
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programming
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Saturday, December 23, 2017
Difference between Method Overloading and Overriding in Java?
Method Overloading vs Method Overriding
Though the name of the method remains same in the case of both method overloading and overriding, main difference comes from the fact that method overloading is resolved during compile time, while method overriding is resolved at runtime. Also rules of overriding or overloading a method are different in Java. For example, a private, static and final method cannot be overriding in Java but you can still overload them. For overriding both name and signature of the method must remain same, but in for overloading method, the signature must be different. Last but not the least difference between them is that call to overloaded methods are resolved using static binding while the call to overridden method is resolved using dynamic binding in Java.
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How to remove duplicates elements from ArrayList in Java
You can remove duplicates or repeated elements from ArrayList in Java by converting
ArrayList into HashSet in Java. but before doing that just keep in mind that
Set doesn't preserver insertion order which is guaranteed by List,
in fact that’s the main difference
between List and Set in Java. So when you convert ArrayList to HashSet all
duplicates elements will be removed but insertion order will be lost.
Let’s see this in action by writing a Java program to remove duplicates from ArrayList
in Java. In this Java collection tutorial, we will see both approaches of deleting
duplicates from ArrayList e.g using Hashset
and LinkedHashSet and compare the order of elements in final ArrayList which
contains no duplicates.
Labels:
core java
,
java collection tutorial
,
programming
Location:
United States
Friday, December 22, 2017
How to find second highest or maximum salary of Employee in SQL - Interview question
How to find the second highest or second maximum salary of an Employee is one of the most frequently asked SQL interview questions similar to finding duplicate records in table and 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 the 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.
Labels:
database
,
database interview questions
,
interview questions
,
mysql
,
SQL
,
SQL Interview Questions
Location:
United States
10 points about instanceof operator in Java with example
The instanceof operator in Java is used to check if an object belongs to a particular type or not at runtime. It's also a built-in keyword in Java programming language and mostly used to avoid ClassCastException in Java. It is used as a safety-check before casting any object into a certain type. This operator has a form of object instanceof Type and returns true if the object satisfies IS-A relationship with the Type i.e. object is an instance of class Type or object is the instance of a class which extends Type or object is an instance of a class which implements interface Type.
How to print Floyd's Triangle in Java with Example
There are lots of programming exercises in Java, which involves printing a particular pattern in console, one of them is printing Floyd triangle in the console. In Floyd triangle, there are n integers in the nth row and a total of (n(n+1))/2 integers in n rows. This is one of the most simple patterns to print but helpful in learning how to create other more complex patterns. The key to develop patterns is using nested loops and methods like System.out.print() and println() appropriately. Actually, pattern-based programming tasks are originally designed to master loops in programming.
XPath Tutorial - How to select elements in XPATH based on attribute and element value example
In this XPATH tutorial we will see example of selecting elements based
upon its value or attribute value. We will see how to select between two
elements based upon value of its child elements or based upon value of its
attribute. XPATH is an important concept to understand if you are working with
XML files. Most of Back-office platform relies on XML
files for transporting data from one system to other and if you are working
on any back-office or middle office system in Java or .NET, its important to know
about XPATH and be able to use XPATH to select data from XML. Some time back I
have shared my XPATH
notes for Java programmer and this example shows true power of XPATH as how convenient its to made selective decision.
Labels:
core java
,
Java xml tutorial
,
xml
Location:
United States
Constructor Chaining in Java - Calling one constructor from another using this and super
Constructor Chaining in Java
In Java, you can call one constructor from another and it’s known as constructor chaining in Java. Don’t confuse between constructor overloading and constructor chaining, former is just a way to declare more than one constructor in Java. this and the super keyword is used to call one constructor from other in Java. this() can be used to call another constructor of the same class while super() can be used to call a constructor from superclass in Java. Just keep in mind that this() in reality calls the no-argument constructor of the same class while this(2) calls another constructor of the same class which accepts one integer parameter.
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core java
,
core java interview question
Location:
United States
Thursday, December 21, 2017
How to Escape String Literal in Java Using Eclipse IDE
Whenever you paste String in Eclipse which contains escape characters, to store in a String variable or just as
String literal it will ask to manually escape special
characters like single quotes, double quotes, forward slash, etc. This
problem is more prominent when you are pasting a large chunk of data which
contains escape characters like a whole HTML or XML
file, which contains lots of single quotes
e.g. ‘’ and double quotes “” along with forwarding slash on closing tags. It’s
very hard to manually escape all those characters and it's pretty annoying as well.
While writing JUnit
test for XML documents, parsing, and processing I prefer to have the whole XML
file as String in the Unit test, which pointed me to look for that feature in
Eclipse.
Location:
United States
Invalid initial and maximum heap size in JVM - How to fix
I was getting "Invalid initial heap size: -Xms=1024M" while starting JVM and even after changing maximum heap size from 1024 to 512M it keeps crashing by telling "Invalid initial heap size: -Xms=512m , Could not create the Java virtual machine". I check almost everything starting from checking how much physical memory my machine has to any typo in JVM parameters, only to find out that instead of M, I had put MB there. Java accepts both small case and the capital case for Kilo, Mega, and Gigs. you can use m or M, g or G, etc but never used MB, GB, or KB. Similar problem can occur with maximum heap size specified by -Xmx. Also from Java 6 update 18, there is a change in default heap size in JVM.
Labels:
core java
,
debugging
,
error and exception
,
JVM Internals
Location:
United States
Financial Information Exchange (FIX) Protocol Interview Questions Answers
Financial Information Exchange (FIX) Protocol Interview Questions and Answers
Some more Fix protocol interview question , I will put answer along when I'll get some time for now just questions :)
Now I have updated it with answer, Please let me know if you have any doubt, or you have other questions, you can also contribute by any question asked during any FINANCIAL INFORMATION EXCHANGE (FIX) protocol interview.
What do you mean by Warrant?
Warrant is a financial product which gives right to holder to Buy or Sell underlying financial security, its similar to option with some differences e.g. Warrants are normally issued by banks while options are primarily traded in exchange.
Some more Fix protocol interview question , I will put answer along when I'll get some time for now just questions :)
Now I have updated it with answer, Please let me know if you have any doubt, or you have other questions, you can also contribute by any question asked during any FINANCIAL INFORMATION EXCHANGE (FIX) protocol interview.
What do you mean by Warrant?
Warrant is a financial product which gives right to holder to Buy or Sell underlying financial security, its similar to option with some differences e.g. Warrants are normally issued by banks while options are primarily traded in exchange.
Location:
United States
Wednesday, December 20, 2017
Java.net.BindException: Address already in use: JVM_Bind:8080 Solution
java.net.BindException: Address already in use: JVM_Bind is a common exception in Java with application trying to connect on a particular port and some other processes either Java or non Java is already connected on that port. You can get "Address already in use: JVM_Bind" error while doing remote debugging in Java in Eclipse, when Eclipse trying to connect to remote Java application when you are starting tomcat and another instance of tomcat is listening on port 8080 you will get java.net.BindException: Address already in use: JVM_Bind:8080.
Labels:
core java
,
error and exception
Location:
United States
SQL query to copy, duplicate or backup table in MySQL, Oracle and PostgreSQL database
Many times we need to create backup or copy of tables in databases like
MySQL, Oracle, or PostgreSQL while modifying table schema like adding new
columns, modifying columns, or dropping columns. Since its always best to have a
backup of a table that can be used in any event. I was looking for an easy way
to create an exact copy or duplicate tables which must be the same in schema as well
as in data, similar to creating a copy of the folder. Luckily there is an easy SQL
query "CREATE table table_name AS" which allows you to create exact
copy of table by executing just one SQL query. Yes, you read it
correctly, no tool is required to create backup of table you just need to
execute an SQL query.
Labels:
database
,
mysql
,
programming
,
SQL
,
SQL Interview Questions
Location:
United States
Tuesday, December 19, 2017
Why main method is public static in Java
Main method in Java is the first programming method a Java programmer knows when he starts learning Java programming language.have you ever thought about why main method in Java is public, static and void, of-course Yes, since most of us first learn C and C++ than we move to Java in our programming path we familiar with main method but in Java main method is slightly different it doesn't return any value like in C it returns int, main method is public static and void Why? In this post we will try to find answer to these questions and have an idea of one of the most popular questions in Java why main method is declared Static.
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core java
,
core java interview question
Location:
United States
How to sort HashMap by key and value in Java - Hashtable, Map Example Tutorial
Sorting HashMap in Java is not as easy as it sounds because unfortunately Java API doesn't provide any utility method to sort HashMap based on keys and values. Sorting HashMap is not like sorting ArrayList or sorting Arrays in Java. If you are wondering why we can not use Collections.sort() method than for your information it only accepts List<E>, which leaves us to write our own utility methods to sort Map in Java. This is true for all types of Map like Hashtable, HashMap, and LinkedHashMap. TreeMap is an already a sorted Map so we don't need to sort it again. Why we need to sort HashMap in Java, Why can't we use TreeMap in place of HashMap is the question appears in most Java programmer's mind when they asked to sort HashMap in Java.
Labels:
coding
,
core java
,
java collection tutorial
,
programming
Location:
United States
Monday, December 18, 2017
Does Java Pass by Value or Pass by Reference - Interview Question
Does Java is pass by value or pass by reference is one of the tricky Java question mostly asked on fresher level interviews. Before debating
whether Java is pass by value or pass by reference lets first clear what is
pass by value and what is pass by reference. This question has its origin on C
and C++ where you can pass function parameter either value or memory address,
where value is stored (pointer). As per Java specification everything in Java
is pass by value whether its primitive value or objects and it does make sense
because Java doesn't support pointers or pointer arithmetic, Similarly multiple inheritance and operator
overloading is also not supported in Java.
Labels:
core java
,
core java interview question
Location:
United States
Sunday, December 17, 2017
Common issue on financial information exchange (FIX) Connectivity
FIX Protocol Session Connectivity
Hi guys, in this post I would like to share my experience with financial information exchange (FIX) Connections which is essential to setup FIX connectivity for trading purposes. Financial information exchange (FIX) Connections used in both Client Connectivity and Exchange connectivity space (in case exchange supports financial information exchange (FIX) Protocol or you are connecting to any broker via FINANCIAL INFORMATION EXCHANGE (FIX) Protocol).
Hi guys, in this post I would like to share my experience with financial information exchange (FIX) Connections which is essential to setup FIX connectivity for trading purposes. Financial information exchange (FIX) Connections used in both Client Connectivity and Exchange connectivity space (in case exchange supports financial information exchange (FIX) Protocol or you are connecting to any broker via FINANCIAL INFORMATION EXCHANGE (FIX) Protocol).
Saturday, December 16, 2017
What is load-on-startup servlet element in web.xml with Example?
load-on-startup is an element that appears inside <servlet> tag in web.xml.4 years back load-on-startup was a very popular servlet interview question because not many Java J2EE developer was familiar with this element and how load-on-startup works inside a servlet container like tomcat or WebSphere. In this J2EE Tutorial, we will see what is a load on startup, how to use load-on-startup element, and what are different values we can configure for loadOnStartup inside web.xml.
Location:
United States
Friday, December 15, 2017
Inversion of Control and Dependency Injection design pattern with real world Example - Spring tutorial
Inversion of Control and Dependency Injection is a core design pattern of Spring framework. IOC and DI design pattern is also a popular design pattern interview question in Java. As the name suggest Inversion of control pattern Inverts responsibility of managing the life cycle of the object e.g. creating an object, setting their dependency etc from application to a framework, which makes writing Java application even more easy. The programmer often confused between IOC and DI, well both words used interchangeably in Java world but Inversion of Control is a more general concept and Dependency Injection is a concrete design pattern.
Labels:
design patterns
,
spring
,
spring interview questions
Location:
United States
Java Error : 'javac' is not recognized as an internal or external command
So you are trying to compile your Java source file and getting "'javac' is not recognized as an internal or external command". If this is your first Java program or HelloWorld than I suggest going through How to compile and run HelloWorld in Java because that explains what do you need before you compile and run any Java program. If you have crossed that level and knows about How to set PATH in Java then there is something wrong while setting PATH in Java. Anyway let's see when do you get this error and from where does 'javac' is not recognized as an internal or external command comes.
Labels:
core java
,
debugging
,
error and exception
,
programming
Location:
United States
Thursday, December 14, 2017
How to find duplicate records in a table on database - SQL tips
How to find duplicate records in table is a popular SQL interview
question which has been asked as many times as difference
between truncate and delete in SQL or finding second highest salary of
employee. Both of these SQL queries are must know for any one who is appearing
on any programming
interview where some questions on database and SQL are expected. In order
to find duplicate records in database
table you need to confirm definition of duplicates, for example in below contact table
which is suppose to store name and phone number of contact,
a record is considered to be duplicate if both name and phone number is same
but unique if either of them varies.
Labels:
database
,
database interview questions
,
mysql
,
programming
,
SQL
,
SQL Interview Questions
Location:
United States
5 Example of kill command in UNIX and Linux
Kill command in UNIX and Linux is normally used to kill a suspended or hanging process or process group. Though kill is mainly associated with kill operation its merely a signal transporter and can send specified signals to specified processes in UNIX or UNIX like systems e.g. Linux, Solaris, or FreeBSD. Like in windows when we see a particular process hung the system we go to the task manager find the process and kill it, similarly, in UNIX and Linux we first find the process ID (PID) of the offending process and then kill it.
Location:
United States
Wednesday, December 13, 2017
java.lang.ClassNotFoundException: oracle.jdbc.driver.OracleDriver - cause and solution
java.lang.ClassNotFoundException: oracle.jdbc.driver.OracleDriver Exception comes when you try to connect the Oracle database from Java program and Oracle driver is not available in Classpath. We have already seen How to connect Oracle database from Java program and found that, In order to connect to Oracle database, we load and register driver using Class.forName("oracle.jdbc.driver.OracleDriver") and this code loads a class at runtime using Reflection which throws ClassNotFoundException if the class in question e.g. "oracle.jdbc.driver.OracleDriver" is not found.
Labels:
core java
,
error and exception
,
JDBC
Location:
United States
Tuesday, December 12, 2017
How to configure Log4j in Java program without XML or Properties File
Sometime configuring Log4j using XML or properties file looks annoying, especially if your program not able to find them because of some classpath issues, wouldn't it be nice if you can configure and use Log4j without using any configuration file e.g. XML or properties. Well, Log4j people has thought about it and they provide a BasicConfigurator class to configure log4j programmatically, thought this is not as rich as there XML and properties file version is, but it's really handy for quickly incorporating Log4j in your Java program.
What is Constructor in Java with Example – Constructor Chaining and Overloading
What
is constructor in Java
Constructor in Java is block of code which is executed at the time of
Object creation. But other than getting called, Constructor is entirely
different than methods and has some specific properties like name of constructor
must be same as name of Class. Constructor also can not have any return type,
constructor’s are automatically chained by using this
keyword and super. Since Constructor is used to create object, object
initialization code is normally hosted in Constructor. Similar to method you
can also overload
constructor in Java. In this Java tutorial we will some important points
about constructor in Java which is worth remembering for any Java programmer.
Labels:
core java
,
object oriented programming
Location:
United States
Java TreeMap Tutorial: 15 Example of TreeMap in Java
TreeMap in Java is a SortedMap and it maintains Sorting order when you insert object on it. You can specify Sorting order while Creating TreeMap by providing an explicit Comparator to TreeMap. Basically you can create TreeMap in Java by different ways, a TreeMap with natural sorting order, and TreeMap with custom Sorting Order by providing Comparator, Copying Sorting order from other SortedMap etc. TreeMap has specific constructor for these conditions. We will see these in section of creating instance of TreeMap in Java.
Labels:
core java
,
java collection tutorial
,
TreeMap
Location:
United States
Monday, December 11, 2017
How to comment uncomment single line and block of code in Java - Eclipse Tips Tricks
Knowing Eclipse shortcut to comment and uncomment single line or block
of code can save you a lot of time while working in Eclipse. In fact I highly
recommend every Java programmer to go through these top
30 Eclipse shortcut and 10
java debugging tips in Eclipse for improved productivity. If you are Java
programmer, coding in Eclipse and want to comment and uncomment single line or
block of code quickly you can either use ctrl + / to comment
a single line and subsequently uncomment a commented line. If you want to
comment a block of code or a complete method, you have two option you can
either line comment (//) all those selected lines or block
comment (/* */) those lines.
Labels:
Eclipse
,
java
,
programming
Location:
United States
Sunday, December 10, 2017
9 Things about Null in Java
Java and null are uniquely bonded. There is hardly a Java programmer, who is not troubled by null pointer exception, it is the most infamous fact about. Even inventor of null concept has called it his billion dollar mistake, then why Java kept it? Null was there from long time and I believe Java designer knows that null creates more problem than it solves, but still they went with it. It surprise me even more because Java's design philosophy was to simplify things, that's why they didn't bothered with pointers, operator overloading and multiple inheritance of implementation, they why null. Well I really don't know the answer of that question, what I know is that, doesn't matter how much null is criticized by Java developers and open source community, we have to live with that.
How to split a comma separated String in Java? Regular Expression Example
You can use the String.split() function or StringTokenizer class to split a comma-separated String in Java. Since splitting a String is a very common functionality, Java designers have provided a couple of split() method on java.lang.String class itself. These split() function takes a regular expression and split the String accordingly. In order to parse a comma-delimited String, you can just provide a "," as a delimiter and it will return an array of String containing individual values. The split() function internally uses Java's regular expression API (java.util.regex) to do its job.
Labels:
core java
,
Java Regular Expression tutorials
,
Java String
Union and Intersection of two Set in Java - Google Guava Example
Google
Guava is an open source library which provides lots of useful utility to Java
programmer, one of them is easy way to find
intersection and union of two Set in Java. You might have used Google
Guava for other functionality e.g. for overriding
toString in easy way or Immutable Collection provided by Guava library.
Along with Apache commons and Spring, Google Guava is a library you definitely want
to include in your Project. Guava provides couple of static
method to operate on Set
in Java on package com.google.common.collect.Sets. There are
two methods called intersection() and union() which
provides intersection and union of two
Sets in Java. In this example we have used HashSet
as Set implementation but it will work with any Set implementation e.g. TreeSet
or LinkedHashSet.
Labels:
core java
,
java collection tutorial
,
programming
Location:
United States
Saturday, December 9, 2017
How to parse String to Enum in Java | Convert Enum to String with Example
Converting Enum into String and parsing String to Enum in Java is becoming a common task with growing use of Enum. Enum is very versatile in Java and preferred the choice to represent bounded data and since is almost used everywhere to carry literal value it's important to know how to convert Enum to String in Java. In this article, we will see both first converting Strings to Enum in Java and then Change an Enum to String in Java with Example. I thought about this Enum tutorial when I wrote 10 Examples of Enum in Java. I missed String to Enum conversion and one of reader pointed out that. So here we have now.
Location:
United States
Friday, December 8, 2017
How ClassLoader Works in Java
Java class loaders are used to load classes at runtime. ClassLoader in Java works on three principles: delegation, visibility, and uniqueness. Delegation principle forward request of class loading to parent class loader and only loads the class if the parent is not able to find or load the class. Visibility principle allows child class loader to see all the classes loaded by parent ClassLoader, but parent class loader can not see classes loaded by a child. Uniqueness principle allows one to load a class exactly once, which is basically achieved by delegation and ensures that child ClassLoader doesn't reload the class already loaded by a parent. Correct understanding of class loader is a must to resolve issues like NoClassDefFoundError in Java and java.lang.ClassNotFoundException, which are related to class loading.
Labels:
core java
,
core java interview question
,
JVM Internals
Location:
United States
Thursday, December 7, 2017
Top 5 FIX Protocol Data Dictionaries and Online FIX References
While you work on FIX Protocol you need a handy FIX Data dictionaries or what we called fixionary in order to refer for exact details related to the particular message type, particular fix tag and what does a particular value of tag means. Without FIX data dictionary or fix wiki it’s very hard to work especially when you are dealing with different fix protocol versions like FIX 4.0, FIX 4.1, FIX 4.2 and FIX 4.4. In this FIX Protocol article, we will explore some of the free available fixionaries or fix protocol reference guides. FIX data dictionary is a must have development tool for FIX protocol developers.
Top 10 JDBC Interview questions answers for Java programmer
JDBC
Interview Question and Answer
JDBC Questions are an integral part of any Java interview, I have not seen any Java Interview which is
completed without asking the single JDBC Interview question, there is always at least one or two questions from JDBC API. Some of the popular questions like Why
you should use PreparedStatement in Java,
Difference between PreparedStatement and CallableStatement in Java and
few questions is related to improving the performance of the JDBC layer by applying
some JDBC
performance tips. In this article, I have summarized a few frequently asked
questions in JDBC, they range from easy to difficult and beginner to advanced.
Labels:
core java
,
core java interview question
,
JDBC
Location:
United States
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