How to use Java Enum in Switch Case Statement - Exampel Tutorial

Java Enum in Switch Case Statement
Yesterday, some one ask me Can we use Java Enum in Switch case ? Obviously, he was learning Enum and not aware that How powerful Enum in Java is. Yes, You can use Enum in Switch case statement in Java like int primitive. If you are familiar with enum int pattern, where integers represent enum values prior to Java 5 then you already knows how to  use Switch case with Enum. Using Java Enum in Switch case is pretty straightforward, Just use Enum reference variable in Switch and Enum constants or instances in CASE statement. In this Java tutorial we will see one example of How to use Enum in Switch statement in Java. By the way Enum is feature rich in Java, Enum can implement interface in Java, Enum can override method in Java, Enum can have constructor in Java and Enum is full functional Type like class or interface. Programmers use Enum with different ways. One of the best example of Enum in Java is replace enum int pattern and enum String pattern. You can also use Enum to write Thread-safe Singleton in Java.

Java program to add two numbers - Example code how to

How to add two numbers in Java
In this Java program tutorial, we will add two numbers provided from the user on the command line. Write a Java program to add two numbers in Java is a common programming exercise for programmers and mostly asked in college exams , school homework, and Java courses as well. There are a different variant as well where you need to ask that write a method to add two numbers e.g. sum(int a, int b) and may ask you to get numbers as input from the user. Taking user input is a little bit tricky for Java programmers but once you know how to do that, it's rather simple.

NullPointerException in Java - A nemesis of Programmer - Tips to fix and prevent

NullPointerException in Java is a unchecked Exception defined in java.lang package and comes when a member of a an object either field or method is called on a object which is null. null is a keyword in Java which means nothing and calling method on Object whose value is null will result in NullPointerException. Since default value of Object is null, if you call any method or access any field on an Object which is not initialized will throw NullPointerException. Some programmer get confused with name as well, Since Java does not support pointers, How can you have NullPointerException in Java? Well java.lang.NullPointerException doesn't have anything to do with pointers, it just an Exception in Java. If you look at it more deeply, NullPointerException is an unchecked Exception and it's not mandatory to provide Exception handling code for it using try, catch and finally. In fact most of NullPointerException comes because of programming errors. See most common cause of NullPointerException to find out most common scenario where NullPointerException comes in Java. In this Java article we will not only see What is NullPointerException but also How to avoid NullPointerException and How to fix java.lang.NullPointerException in Java.

ArrayList vs Vector in Java - Interview Question

ArrayList vs Vector in Java
ArrayList and Vector is two most widely used Collection class in Java and used to store object in ordered fashion. Every Java programmer which is introduced to Java Collection Framework either started with Vector or ArrayList. For beginners Difference between Vector and ArrayList in Java  and LinkedList vs ArrayList are two most  popular Java Interview question. ArrayList vs Vector is not only important on interview perspective but also on effective use of Java Collection API. After reading this article you will know when to use Vector in Java, When to use ArrayList in Java and would be able to compare ArrayList vs Vector over several important parameters e.g. Speed, Synchronization, Code quality etc. Before seeing difference on Vector vs ArrayList, let's What is common between the.

Java String Matches Example - Regular Expression Tutorial

String Matching Example in Java
String matches method in Java can be used to test String against regular expression in Java. String matches() method is one of the most convenient way of checking if String matches to a regular expression in Java or not. Quite often we need to write code which needs to check if String is numeric, Does String contains alphabets e.g. A to Z or a to Z, How to check if String contains a particular digit 6 times etc. There are so many cases in Java programming where we need regular expression. If you are familiar with Java's regular expression API than you must know about java.util.regex.Pattern and java.util.regex.Matcher class, these class provides regular expression capability to Java API. matches method of String class actually delegate request to these classes. Anyway regular expression can be best learn by seeing few examples and this is what we are going to do in this Java String matches example tutorial.

Java program to get SubList from ArrayList - Example

Sometimes we need subList from ArrayList in Java. For example, we have an ArrayList of 10 objects and we only need 5 objects or we need an object from index 2 to 6, these are called subList in Java. Java collection API provides a method to get SubList from ArrayList. In this Java tutorial, we will see an example of getting SubList from ArrayList in Java. In this program, we have an ArrayList which contains 4 String objects. Later we call ArrayList.subList() method to get part of that List.

DOM vs SAX Parser in Java - XML Parsing in Java

DOM vs SAX parser in Java
DOM and SAX parser are two most popular parser used in Java programming language to parse XML documents. DOM and SAX concept are originally XML concept and Java programming language just provide an API to implement these parser. Despite both DOM and SAX are used in XML parsing, they are completely different to each other. In fact difference between DOM and SAX parser is a popular Java interview question asked during Java and XML interviews. DOM and SAX parser has different way of working, which makes Java programmer to understand difference between DOM and SAX parser even more important. Careless use of DOM parser may result in java.lang.OutOfMemoryError if you try to parse a huge XML file and with small heap size while careless use of SAX parser may result in poor performance while parsing small and medium sized XML files with good enough heap space in Java. In this Java article we will compare DOM and SAX parser and learn difference between them.

Java Program to convert String ArrayList to String Array

Converting String ArrayList into String array is very common programming task in Java. you often need to convert Array to Array List in Java  and vice-versa. In this Java program, we will How to convert String ArrayList to String array. This is also a common programming exercise which is asked too many Java programmers in various Java related courses. It’s also worth noting that ArrayList in Java is internally backed by array and Array in Java are objects much like String which is also an Object in Java. In this Java program, we first create an ArrayList which stores name of months as String e.g. Jan, Feb, and Mar. Later we use ArrayList  toArray() method to convert ArrayList into an array.

What is difference between Overloading and Overriding in Java

Overloading vs Overriding in Java
In last couple of articles we have seen What is method overloading and What is method overriding in Java and now we will see What is difference between overloading and overriding in Java. Overloading vs overriding is one of those frequently asked Java interview question which can not be ignored. Overloading vs Overriding has appeared in almost every Java interview, mostly at beginner and intermediate level e.g. 2 to 4 years experience. In fact most of those tricky Java interview Question came from Overloading and Overriding. It's one of the tricky fundamental to understand. In this article we will some important difference between Overloading and Overriding which not only help to understand concept better but also serves as good recap for Java interviews.

Top 10 Java Web Service Interview question answers

Java Web Services Questions and Answers
Web Services interview questions are part of J2EE interviews for jobs which are looking some experience in Java web services Space. Most of the Web services questions come from two different way of implementing Web Services e.g. SOAP and REST. SOAP is an standard and mature way of calling Web Services which uses XML while REST is a new way of implementing Web Services which is based on HTTP protocol. In fact REST Web Service interview questions are getting more and more popular on web services interviews in Java, So if you are going for any Java J2EE interview which require some web service experience, be prepare with both SOAP and REST Web services questions. Following is list of Java web services interview questions which I have prepared for practice. Answers of these web services questions can be easily found in many places on Internet and I will update this list whenever I have new web services interview question. If you guys find any interesting tricky or tough Java web service question asked in Interviews then please share with us :

keytool command examples Java - add view ssl certificate in keyStore trustStore

keytool command in Java is a tool for managing certificates into keyStore and trustStore which is used to store certificate and requires during SSL handshake process. By using keytool command you can do many things but some of the most common operation is viewing certificate stored in keystore, importing new certificates into keyStore, delete any certificate from keystore etc. For those who are not familiar keyStore, trustStore and SSL Setup for Java application , Here is a brief overview on What is a trustStore and keyStore in Java. Both trustStore and keyStrore is used to store certificate signed by signer authority or CA (Certificate authority), with keyStore additionally storing personal certificate for client which is used during client authentication on SSL handshake process if its enable. In this article we will see some basic example of keytool command in Java to find how many certificates we have in keyStore , viewing those certificates, adding new certificates and deleting old certificates from keyStore or trustStore in Java.

10 Linux and UNIX Interview Questions and Answers asked in Wipro TCS Capegemini

UNIX and Linux Interview Questions and Answers
Questions from various UNIX operating systems e.g. Solaris, Linux, IBM AIX or any other UNIX operating system is asked on different support and programming interviews. I have always seen few interview questions from Linux and UNIX along with SQL in almost every Java programming interviews. You just can not afford not to prepare questions from UNIX and Linux until your Job absolutely doesn't require any work in UNIX operating system. I have collected many UNIX command interview questions and already shared them but I found that except system admin jobs, many programming job interviews only focus on general UNIX commands e.g. chmod, find or grep and fundamentals like finding files and directories, managing file space, networking commands, checking process status and managing file permissions.

Difference between ServletConfig and ServletContext in JSP Servlet J2EE

Difference between ServletConfig and ServletContext
ServletContext and ServletConfig these two are important interface of Servlet API which is used by Java J2EE programmer during web application development. Correct understanding of What is ServletContext and ServletConfig is very important for any J2EE application developer. Apart from that Difference between ServletContext and ServletConfig are a popular Servlet JSP interview questions and mostly asked on both fresher and experienced Java programmer during J2EE interviews. Both ServletContext and ServletConfig are basically configuration objects which are used by servlet container to initialize various parameter of web application. But they have some difference in terms of scope and availability so first we see what is ServletContext and ServletConfig objects are and then we will see difference between ServletConfig and ServletContext in Java J2EE.

What is blank final variable in Java - Example

What is blank final variable in Java
Blank final variable in Java is a final variable which is not initialized while declaration, instead they are initialized in a constructor. Java compiler will complain if a blank final variable is not initialized during construction. If you have more than one constructor or overloaded constructor in your class then blank final variable must be initialized in all of them, failing to do so is a compile time error in Java. Alternatively, you can use constructor chaining to call one constructor from other using this keyword, in order to delegate initialization of blank final variable in Java. In this Java tutorial, we will see What is blank final variable in Java and a code example on How to use a blank final variable.

Rules of Method Overloading and Overriding in Java

The overloading and overriding rule in JavaSince you can either overload or override methods in Java, its important to know what are the rules of overloading and overriding in Java. any overloaded method or overridden method must follow rules of method overloading and method overriding to avoid compile time error and logical runtime errors;  where you intend to override a method but method get overloaded. That is not uncommon and happen several times when Java programmer tries to override equals in Java or  overriding compareTo method in Java while implementing Comparable interface, which accepts Object type of argument. From Java 5 onwards which introduces @Override annotation along with Enum, Generics and varargs method you can completely avoid that problem.

Java program to find square root of number - Example Code

Java program for square root or a number in Java
How to write Java program to find square root of a number is common Java programming exercise which many institute use in there Java course along with Java program to print Fibonacci series and How  to find Armstrong numbers in Java, which we have seen earlier.  Java program for square root is also a popular question during college semester exams and  various programming tests. If you are familiar with Java API then writing a Java program which can find square root of number using java.lang.Math class is not difficult. You just need to pass a double value and it returns a double which is square root of number you passed.  In next section we will see complete code example of finding square root of a number from Java program. Another Java coding questions which is very popular and related to programming exercise is writing Java program to find prime numbers, if you are going to appear in Java interviews then its worth looking.

What is difference between interface and abstract class in Java

What is abstract class and interface in Java
The difference between abstract class and interface in Java is one of the tricky Java interview question and mostly appear in core Java interviews. It has become now even trickier after Java 8 introduced default methods and allowed interfaces to have both default and static methods. Even though both interface and abstract class is a way to achieve abstraction in Java, there are significant differences between them, which you will learn in this article. Some time interviewer also not just focus on key differences between abstract class and interface in Java but he is also interested in some practical experience e.g. when to use interface in Java and when to use abstract class is Java. This is actually the tricky part of this interview question and  you must have a good understanding of what is an interface and abstract class in Java and how to use them. Anyway in this Java article we will first see some syntactical difference between interface and abstract class in Java programming language and later we will see where to use abstract class and interface.

Autoboxing, Enum, Generics, Varargs methods - Java 5 Features Quick Overview

What is Autoboxing , Generics, Enum and Varargs method in Java 5
Java 5 introduces Autoboxing, Generics, varargs and Enum along with several other features and improvement. It's been few years when Java programming language was enhanced with these features but still Java programmer thing Autoboxing, Enum, Generics or Variable arguments as an advanced feature and afraid to learn them. They are very much part of Java fundamentals just like Abstraction, Inheritance, Encapsulation and Polymorphism are part of Object oriented programming concepts. It's important to understand what are these feature and How to use them, even if you don't use them in your code, you may have to work on someone else code which is written in Java 5 and uses Generics Collection, Autoboxing quite frequently. In this Java 5 tutorial, we will see the brief overview of Java 5 features like Generics, Enum, Autoboxing and unboxing and variable arguments methods along with examples and explanations.

What is Struts Action Class in Java J2EE - How to use

What is Action class in Struts
Struts in java is a framework, used to make web application its is based on Model View Controller or MVC design Pattern where Model represent the internal state and action used to change the state view represent presentation component and a controller is responsible for receiving the request from the client and decide which business logic should be called. Basically, Struts have different classes to represent this Model, View, and Controller we call them as Action, Action Form, and Action Servlet. So

Model – Action classes
View - Action form classes
Controller – Action Servlet classes

In this article, we are focusing on the Model layer of struts framework. Action class is used to provide an interface to application model layer.  What is Action class and how to use Action class is also a popular Struts interview Question asked in various J2EE interviews.

What is CopyOnWriteArrayList in Java - Example Tutorial

CopyOnWriteArrayList vs Array List in Java
CopyOnWriteArrayList is a concurrent Collection class introduced in Java 5 Concurrency API along with its popular cousin ConcurrentHashMap in Java. CopyOnWriteArrayList implements List interface like ArrayList, Vector and LinkedList but its a thread-safe collection and it achieves its thread-safety in a slightly different way than Vector or other thread-safe collection class. As name suggest CopyOnWriteArrayList creates copy of underlying ArrayList with every mutation operation e.g. add or set. Normally CopyOnWriteArrayList is very expensive because it involves costly Array copy with every write operation but its very efficient if you have a List where Iteration outnumber mutation e.g. you mostly need to iterate the ArrayList and don't modify it too often. Iterator of CopyOnWriteArrayList is fail-safe and doesn't throw ConcurrentModificationException even if underlying CopyOnWriteArrayList is modified once Iteration begins because Iterator is operating on separate copy of ArrayList. Consequently all the updates made on CopyOnWriteArrayList is not available to Iterator. In this Java Collection tutorial we will see What is CopyOnWriteArrayList in Java, Difference between ArrayList and CopyOnWriteArrayList in Java and One simple Java program example on How to use CopyOnWriteArrayList in Java.

Java Collection interview Questions Answers | Java Collection FAQ

Java Collection Framework interview questions and answers contains questions from popular Java collection classes e.g. HashMap, ArrayList, HashSet, ConcurrentHashMap and legacy collection classes like Vector and Hashtable. Interview questions from Java Collection framework is one of the most asked concept on any Core Java interview or J2EE interview at both beginners, experienced and intermediate level e.g. 2 to 4 years experienced Java programmer. In order to answer interview questions from Java collection framework, You need a good knowledge of various Collection interfaces e.g. Map, List and Set and familiarities with there frequently used implementation e.g. HashMap, Hashtable, TreeMap  from Map, ArrayList, LinkedList and Vector for List interface and HashSet, TreeSet of Set interface. Questions related to Iterating collection , modifying Collection and thread-safety of Collection is also popular area from where Java collection interview Questions asked during interview. In this List of Java collection interview questions and answers, we will see questions from all above area. I have also included some questions from new Concurrent collection classes introduced in Java 5 e.g. ConcurrentHashMap and CopyOnWriteArrayList.

Top 10 tough core Java interview questions answers programming

tough core Java interviews questions and answers
What is tough core java interview question ? Why do people look for tough Java questions before going for an interview? well, I don't think I need to answer these tough questions because it's pretty natural to prepare for tough questions even if you are not expecting tough questions from core Java. If you are prepared for tough and tricky Java interview question than you feel more confident and answer other Java interview question with confidence. On the other hand, if you are not prepared for tough and tricky core Java questions than seeing them on Java interview or written test may surprise you. But the definition of tough core Java questions is not universal, same Java question which is easy for one programmer might be tough for other Java programmer. That's why it's best to prepare your own list of tough interview questions before appearing on any Java job interview. In this article, I am going to share you with my Top 10 tough core Java interview questions and answers, which may help you in Java interview.

What is new in Java 7 - Top 5 JDK 7 feature

What is new in Java or JDK 7
It's close to a year now JDK 7 or Java 7 has been released, still programmer asks What is new in Java 7 ? What is the best feature introduced in JDK7, where is the list of all Java 7 new feature etc? I thought to let's document Top 5 new features introduced in Java 7 for easy reference, this will not only answer What is new in Java 7 but also provide a quick overview of What are those features in Java 7.  Java 7 introduced many new features in Java programming language like try catch with a resource, String in Switch etc but it also makes a lot of change on Java Development API by introducing new File API in Java and several other minor changes. E.g. you can now find hidden files from Java program without applying any hack. anyway let's see my list of Top 5 Java 7 features :

Top 18 Java Design Pattern Interview Questions Answers for Experienced

Design pattern interview question in Java
design pattern interview question are integral part of any good list of core Java interview questions. Java is a popular Object oriented programming language and have lots of design pattern and design principles, contributed by many developers and open source framework. As a Java programmer its expected from you to know OOPS concept like Abstraction, Encapsulation and polymorphism, What is design pattern in Java, Some popular Java design pattern and most importantly when to use those design pattern in Java application. purpose of asking design pattern interview question in Java is to check whether Java programmer are familiar to those essential design patterns or not. Design patterns in Java interviews are as important as multi-threading, collection and programming questions. If you are senior or experienced Java programmer than expect more complex and tough design pattern in Java interview e.g. Chain of responsibility design pattern and solving real time software design questions.

Palindrome: Java program to check number is palindrome or not

How to find if number is palindrome in Java
Checking whether a number is palindrome or not is a classical Java homework exercise. When you start learning Java programming most institute which teach Java  programming provides these classical Java programs like How to find Armstrong number in Java or how to find Fibonacci number in Java using recursion etc. Write a Java program to check if number is palindrome comes from same category. For those who are not familiar with palindrome numbers, palindrome number is a number which is equal to reverse of itself. For example 121 is a palindrome because reverse of 121 is 121, while 123 is not a palindrome in Java because reverse of 123 is 321 and 121!=321. Finding palindrome number is easy in Java, you just need to develop logic to reverse a number in Java. Thankfully Java provides couple of arithmetic operators like remainder(%) operator also known as modules operator, which returns remainder in division operator and division operator(/) which returns quotient. By using remainder and division operator in Java we can create program to check if number is palindrome or not.