Top 21 Maven Interview Questions Answers for Java Developers

Hello guys, for a Java developer, Maven in one of the essential tool and its used to build your Java application. Since most of the Java projects used Maven for building, it is expected from a Java developer that he knows Maven and knows it well. That's why Maven questions are quite common on Java developer interviews but I have seen many Java programmers coming to these interview unprepared and not able to answer most of the questions on tools like Maven, Gradle or even git. When I asked one candidate why don't you prepare for Maven before your Java interviews, he said, I wasn't able to find any list of Maven questions. 

How to enable or disable form elements using jQuery? Examples

In last couple of tutorials you have learned how to get all selected checkbox and radio buttons, and in this tutorial, you will learn how to enable/disable form elements using jQuery. A form element e.g. a textfield, radio buttons and checkbox, all represented using input tag can be enabled or disabled by adding an attribute called "disabled". It's similar to "checked" attribute we have seen for checkbox and radio buttons. If this attribute is not present then element is enable, but if this attribute is present then you can use disabled=true to disable the form element and disabled=false to enable the form elements as shown in our example. Like previous example of checking/unchecking checkbox, you can use prop() jQuery function to enable/disable form element if you are running on jQuery 1.6 or higher version and attr() function if you are running on jQuery 1.5 or lower version. 

How to shuffle a List in Java? Collections.shuffle() Example

Hello guys, if you have a List of numbers and you want to shuff it but don't know how then you have come to the right place. Shuffling is an important technique which is used quite a lot on coding games like number guessing games and card games., The java.util.Collections class provides shuffle() method which can be used to randomize objects stored in a List in Java. Since List is an ordered collection and maintains the order on which objects are inserted into it, you may need to randomize elements if you need them in a different order. Collections.shuffle() method uses default randomness to randomize elements but you also have an overloaded version of shuffle() to provide an instance of the java.util.Random object, which can be used to randomize elements.

How to Compare Two Dates in Java? Check If They Are Equal, Later or Earlier - Examples

There are multiple ways to compare two dates in Java, it also depends on what exactly comparison means. If you are looking to compare two dates to find out whether they are equal or not, then you can simply use the equals() method of java.util.Date class. This method will return true if both dates are equal, precisely both have the same millisecond value. If you are looking to find out whether a date comes before or after another date then you have 3 choices, you can use the compareTo() method of java.util.Date class, or you can use before() and after() method of Date class, or you can use before() and after() method of Calendar class. I suggest leveraging the before() and after() method of the Date class, they are more readable and easy to use.

What is transient variable in Java? Serialization Example

What is a transient variable in Java?
transient variable in Java is a variable whose value is not serialized during Serialization and which is initialized by its default value during deserialization, for example for object transient variable it would be null. This behavior can be customized by using a custom Serialized form or by using the Externalizable interface. A transient variable is used to prevent any object from being serialized and you can make any variable transient by using the transient keyword. You cannot make a local variable transient through and it's only the member variables which can be transient. 

Difference between HashSet and HashMap in Java? Answered

HashSet and HashMap in Java
Hello friends, if you have given Java developer interview then there is good chance that you may have come across questions like Difference between HashSet vs HashMap or HashSet vs TreeSet etc. In this article, we are going to discuss differnece between HashMap and HashSet, two of the popular Collection classes from JDK. The HashSet vs HashMap is a classical Java Collection interview question that focuses on What are differences between HashSet and HashMap in terms of features, usage, and performance. If you are in Java programming even for a year or so, you are likely to be familiar with What is HashSet in Java and What is HashMap in Java, these two are the most popular collection classes. 

What is PATH and CLASSPATH in Java? Path vs ClassPath Example

What is PATH and CLASSPATH in Java
The PATH and CLASSPATH are the two most important environment variables of the Java environment which are used to find the JDK binaries used to compile and run Java in windows and Linux and class files which are compiled Java bytecodes. From my personal experience I can say that PATH and CLASSPATH are the two most problematic things for beginners in Java programming language due to two reasons; first because in most Java courses nobody tells details of what is a PATH and CLASSPATH, What do PATH and CLASSPATH do, What is meaning of setting PATH and CLASSPATH, What happens if we do not set them, Difference between PATH vs CLASSPATH in Java or simply How Classpath works in Java, etc. 

Why is main method public, static, and void in Java? Answer

What is the main method in Java?
The main() method in Java is a special method that is used by JVM to start the execution of any Java program. The main method is also referred to as the entry point of Java application which is true in the case of core Java applications because execution starts from the main() method, but in the case of container-managed environments like Servlet, EJB, or MIDlet this is not true as these Java programs have their own life-cycle methods like init(), service() or destroy() for Servlet's which is used by the container. The main method in Java is run by the main thread which is a non-daemon thread and the Java program runs until the main method finishes or any other user thread is running. 

How to convert JSON String to Java Object using Gson? JSON Deserialization Example

Hello Java Programmers, In the last article, you have learned how to convert a Java object to JSON String and in today's article, you will learn the opposite, i.e. converting a JSON String to a Java object. The first example was known as JSON serialization example and this one is known as JSON deserialization because we are creating a Java object from a String. The idea is very similar to classical Serialization in Java where you convert a Java object to another binary format that can be transported over the network or can be saved in the disk for further usage.

Difference between var, val, and def in Scala? Examples

Hello guys, if you are new to Scala or preparing for Scala interview then you may have come across the question, what is difference between var, val, and def keywords in Scala? This is one of the frequently asked questions from Scala interviews. Even though both var and val keyword is used to declare variables in Scala there is a subtle difference between them. A var is a variable. It’s a mutable reference to a value. Since it’s mutable, its value may change throughout the program's lifetime. On the other hand, the val keyword represents a value. It’s an immutable reference, meaning that its value never changes. Once assigned it will always keep the same value.

3 ways to convert String to JSON object in Java? Examples

It's very common nowadays to receive JSON String from a Java web service instead of XML, but unfortunately, JDK doesn't yet support conversion between JSON String to JSON object. Keeping JSON as String always is not a good option because you cannot operate on it easily, you need to convert it into a JSON object before you do anything else e.g. retrieve any field or set different values. Fortunately, there are many open-source libraries which allows you to create JSON object from JSON formatted String like Gson from Google, Jackson, and json-simple. In this tutorial, you will learn how to use these 3 main libraries to do this conversion with step-by-step examples.

Difference between Correlated and Non-Correlated Subquery in SQL? Examples

Hello guys, the difference between correlated and non-correlated subquery is one of the popular SQL interview question and an important concept for any programmer to learn. The correlated subquery is one of the tricky concepts of SQL. It's similar to recursion in programming which many programmers struggle to understand, but like recursion, it also offers the unique capability to solve many SQL query-based problems like the second-highest salary problem where you need to compare one row of the table to another row. It gives you a different kind of power. The main difference between a regular, non-correlated, and correlated subquery in SQL is in their working, a regular subquery just runs once and returns a value or a set of values that is used by the outer query.

How to sort ArrayList in Java? Examples

Hello Java programmers, sorting ArrayList in Java is not difficult; there are multiple ways to sort a given ArrayList in Java. For example you can use  the Collections.sort() method to  sort ArrayList in ascending and descending order in Java. The  Collections.sort() the method optionally accepts a Comparator. If provided, it uses Comparators' compare() method to compare Objects stored in Collection to compare with each other; in case of no explicit Comparator, Comparable interfaces' compareTo() method is used to compare objects from each other. If objects stored in ArrayList don't implement Comparable, they can not be sorted using the Collections.sort() the method in Java.

What is final modifier in Java? fina class, method, and variable example

Hello Java Programmers, the final variable is a very important concept in Java. It's a modifier that you can apply on variables, methods, and classes and when you apply the final modifier it can make variables immutable, prevent the method from overriding in subclasses, means no polymorphism, and when you make a class final in Java it cannot be extended anymore, taking out Inheritance from the picture. There are both pros and cons of using the final modifier in Java and that's why it's very very important for a Java developer to have an in-depth knowledge of the final modifier in Java and that's what you will learn in this article. 

Best way to Convert Integer to String in Java with Example

Integer to String conversion in Java
There are many ways to convert an Integer to String in Java e.g. by using Integer.toString(int) or by using String.valueOf(int), or by using new Integer(int).toString(), or by using String.format() method, or by using DecimalFormat, String concatenation, or by using StringBuilder and StringBuffer, etc but which one is the best? Some of them we have already seen on my earlier posts e.g. how to convert int to String and converting double to String.  Well, we are going to find the best way to convert Integer to String in Java in this post. 

How to create a ZIP File in Java? ZipEntry and ZipOutputStream Compression Example

Since compressing and archiving old log files is an essential housekeeping job in any Java application environment, a Java programmer should know how to compress files in .zip format and then how to read them programmatically if required. The JDK provides full support to create and read ZIP files in Java. There is a separate package java.util.zip to hold all classes related to zipping and unzipping files and streams. In this series of articles, you will learn how to use those classes like ZipFile, ZipEntry, ZipInputStream, and ZipOutputStream, etc. 

How to add JAR files in Eclipse Project's Build path? Example

In this Java Eclipse tutorial, I will show you two ways to add external JAR files in Eclipse Java projects. Many times we need to use external JAR files in our Java application for different needs like for general purposes you may use Google Guava or Apache Commons. If you are using Spring or Hibernate framework then you need their JAR files as well. In order to use any third-party library or framework, we have to add their JAR files in the classpath, to compile and run our Java programs. Since Eclipse is the most popular IDE for developing Java applications, it's important to know how you can add external JARs into your Java project's build path. 

5 Tips to Fix Exception in thread "main" java.lang.NoClassDefFoundError in Java, Examples

NoClassDefFoundError in Java
The Exception in thread "main" java.lang.NoClassDefFoundError is a common error in Java that occurs if a ClassLoader cannot find a particular class in the classpath while trying to load it. The Exception in thread "main" suggests that this error has occurred in the main thread, the thread which is responsible for running the Java application. This error can occur to any thread, but if it happens in the main thread, then your program will crash because Java program runs only until main() thread is running or any other non-daemon thread is running. As per Javadoc, NoClassDefFoundError can be thrown during the linking or loading of the class file

14 Enum Interview Questions and Answers for 1 to 2 Years Experienced Java Programmers

Hello Java developers, Java Enum is one of the best features of Java Programming language which was first added on the JDK 1.5 Tiger release along with Generics, Autoboxing, and varargs. While the concept of Enum was also present in C Programming language, in Java its much more powerful. Enum in Java represents a fixed number of well-known things like the number of days in a week, the number of months in the calendar year, etc. Unlike C and C++ Enum in Java are much powerful and they are not an integer constant, Instead, Enum is a Type in Java like class or interface which provides compile-time type safety. In this Java Enum tutorial, we will see a couple of important points about Java Enum which help to understand Enum better and get the most out of it. 

How to convert String to char in Java? Example Tutorial

Hello Java Programmers, if you are wondering how to convert a String to char value in Java then you have come to the right place. Earlier, we have seen how to convert a character to String in Java and today we'll learn opposite i.e. converting String object to a character value. You know the difference right? String is an Object while char is a primitive value. So here we are also going to convert a Java object into a primitive value. By the way, this conversion only make sense if String is a single character. For example, you have a String with value "s", how do you convert that to a char 's' in Java (FYI, string literal are quoted inside double quotes in Java, like "c" and character literals are quoted inside single quotes e.g. 'c' in J)? Well, if you know, Java String is made of a character array and java.lang.String class provides a method toCharArray() to retrieve that character array.

How to get current TimeStamp value in Java? Example

Do you know that Java developer Google (now ask ChatGPT) for even the simplest of things? Yes, that's true and I can say it because even I do that :-). Finding the current timestamp value is one of them. In UNIX you can just use the date command to get the current date and time but how do you get that in your Java program? Well, you can get the current timestamp in Java by using the Date and Timestamp class of JDK. Note, there is "s" instead of "S" in Timestamp. Since Date in Java contains both date and time, it can be used as a Timestamp value as well but when you print Date, it shows time in the local timezone

5 Difference between String, StringBuffer, and StringBuilder in Java

Difference between String, StringBuffer, and StringBuilder is probably one of the oldest yet most popular interview question in the history of Java developer interviews. I have personally asked this question almost 4 to 5 times. You will find this question on any list of Java interview questions. I have also included this in my earlier list of core Java questions and Java String questions. If you are preparing for Java interviews, those are handy resources. Now coming back to the answer, although all three classes StringBuffer, StringBuilder, and String are used for representing text data in Java there are some significant differences between them. One of the most notable differences between StringBuilder, StringBuffer, and String in Java is that both StringBuffer and StringBuilder are Mutable classes but String is Immutable in Java. What this means is, you can add, remove or replace characters from StringBuffer and StringBuilder object but any change on the String object like converting uppercase to lowercase or appending a new character using String concatenation will always result in a new String object. 

Difference between include() and forward() methods of RequestDispatcher in Servlert

What is the difference between include and forward methods of RequestDispatcher interface is one of the frequently asked Servlet questions from Java EE interviews and we'll see how you can answer this question on your interview. You get the RequestDispatcher reference either from ServletContext or ServletRequest interface and even though both include() and forward() method allow a Servlet to interact with another servlet, the main difference between include() and forward is that the include() method is used to load the contents of the specified resource (could be a Servlet, JSP, or static resource like HTML files) directly into the Servlet's response, as if it is part of the calling Servlet. 

Base64 Encoding and Decoding Examples in Java 8 and Before

Though, there are a couple of ways to Base64 encode a String in Java e.g. by using Java 6's javax.xml.bind.DatatypeConverter#printBase64Binary(byte[]) or by using Apache Commons Codec's Base64.encodeBase64(byte[) and Base64.decodeBase64(byte[])as shown here, or the infamous Sun's internal base64 encoder and decoder, sun.misc.BASE64Encoder().encode() and sun.misc.BASE64Decoder().decode(), there was no standard way in JDK API itself. That was one of the few missing item (another one is about joining string) which is addressed in Java 8.

How Java achieves platform independence? Answer

Java is a platform-independent language How?
Java a programming language provides platform independence, what does it mean? It means the same Java program can be run on any platform or operating system like Windows, Linux or Solaris without any change. This is a great benefit for someone coming from a platform-dependent programming language like C or C++ whose code needs to be ported for every single platform because they use native libraries, which differ in every platform. Now the question comes how Java achieves platform independence, what makes Java programs running on every platform without any change

10 Difference between Struts 1.x and Struts 2.x framework in Java

What is the difference between Struts 1 and Struts 2 is one of the popular Struts interview questions from Java JEE interviews? If you have mentioned Struts in your CV then you can expect this question on the telephonic or face-to-face round of interviews. Struts 1.x was a very popular MVC framework for Java web applications in the last decade, but when Spring MVC comes it lost a lot of its sheen. Spring framework's dependency injection and inversion of control feature, along with several other template-based features makes it the de-facto framework for developing Java applications. 

When You should Not use Microservice Architecture? (Answer)

 Hello guys, recently while giving interview in one of the big US based Investment bank I was asked about, what are the scenarios when you shouldn't be using Microservices architecture? When I hear this question I was big surprised not because I didn't know the answer but because most of the people ask about using Microservice architecture and this was the first time I am hearing otherwise. To be honest, it's a good question because most of the candidate will prepare about benefirst about Microservice architecture and they may not know when it's not appropriate to use it. Since I have worked in low latency high frequency application, I knew that multiple process means more latency so clearly a Microservices is a big no if you are working on a high frequency low latency application. In those cases you want to do all your calculations inside a single thread or process without even swapping memory to avoid delay. Hence the first answer to this question was, you shouldn't be using Microservice in a low latency application. 

10 Examples of Comparator, Comparable, and Sorting in Java 8

The Comparator class is used to provide code or logic for comparing objects in Java, while sorting a list of objects or a collection of objects. It's close cousin of Comparable which provides natural order sorting e.g. ascending and descending orders for numbers like int, short, long or float, and lexicographic order for String i.e. the order on which words are arranged in dictionaries. The Comparators are used while sorting arrays, lists and collections. You pass logic to compare objects and sorting methods like Collections.sort() use that logic to compare elements until they are arranged in sorted order. 

Difference between static and instance member variables in Java? Answer Example

Hello Java Programmers, In the last article, I had explained some key differences between static and nonstatic methods in Java, and in this part, I'll explain the difference between static and nonstatic member variables in Java. The concept of static remains the same, that doesn't change with method or member variables but there are still some subtle details, which every Java programmer should know and understand. As with static methods, a static member variable belongs to a class and a non-static member variable belongs to an instance. 

23 Java Static Class, Methods and Variables Interview Questions with Answers

The static keyword is one of the essential keyword in Java which represent the concept of static in programming. When you make something static, it is averse to change i.e. it is not dynamic and that is true for static variable, methods and class in Java. When you make a member variable static in Java, JVM assumes that the value of that variable will not change between instance and remain same for all objects of that class, hence it is also referred as class variable. Same is true for static methods, which is bonded during compile time because JVM assumes that their definition will not change because they are static and not virtual.

Top 20 Abstract Class and Method Interview Questions and Answers in Java

Both abstract class and abstract methods are very important concepts in core Java and every Java developer should have good understanding of what they are, when to use them and how to use them. They are also very popular on core Java job interviews as well as on Oracle Java certifications e.g. OCAJP or OCPJP. You will often find a lot of code based questions testing essential core Java concepts based upon abstract class and methods in the real exam. All good mock exam simulators e.g. Whizlabs and Enthuware contains a lot of questions testing and explaining these key concepts. In this article, I have collated some of the frequently asked questions about abstract class and abstract methods in Java. You can review these questions before going for Java interview, both telephonic and face-to-face round. They are also very useful if you are preparing for Oracle Java certification e.g. OCAJP.

Top 6 books to learn Java Virtual Machine, Garbage Collection, and Performance [UPDATED]

In the last couple of years, I have seen a trend of many Java developers wants to learn more and more about JVM internals and how Java Virtual Machine and its different component works. This trend was not so strong in the last decade, but with more and more focus on concurrency, performance, and scalability, Java developer is exploring JVM internals, Garbage collection, and Performance tuning in more detail. Unfortunately, there are not many good books to learn about JVM internals and their different components, but fortunately, we have an excellent Java Virtual Machine specification to learn fundamentals. It is also the most up-to-date reference because Java and JVM are kept changing, especially after Java 10.

Top 5 Design Patterns Books for Java Developers - Best of Lot

Design patterns are an essential topic for object-oriented programmers, like Java and C++ developers. It becomes even more important as your experience grows because everybody starts expecting a lot more from you in terms of writing quality code. I often receive emails from intermediate and senior Java developers about progressing to the next level, like how to become Tech Lead, Team Lead, or software architect; knowledge of design patterns plays an important role in taking more technical responsibility. While the GoF book is the bible for object-oriented design patterns, in my opinion, it is a bit too dry and academic.

Top 5 Books to learn SQL and Database Design in 2024 - Best of Lot

SQL (Structured Query Language) is one of the most essential skills of a programmer. I would rate this skill similar to UNIX if you are a professional programmer because it doesn't matter whether you are Java, C++, or a .NET developer, you are bound to write SQL queries. Since a database is an integral part of any modern Java or Web application, the Interviewer always preferred candidates with excellent SQL skills. Now, the big question comes, how a programmer can learn SQL? Does just knowing how to query a table is enough? If you remember, insert, update, delete, and select, then are you a competent SQL programmer?

Top 10 Free Python Programming Books - Download PDF or Read Online

Every Programmer loves free eBook and free courses, even more, if it comes from renowned technical book publishers like Oreilly and Manning. In the last article, I have shared some of the best free Java programming books, and today I am going to share some of the equally best free Python Programming books. These books are not illegal copies that are uploaded into the internet, but they are legal books, made free by their authors and publishers, much like free Udemy courses, which their instructor made free for educational and promotional reasons. Though these are not full-fledged books but concise eBooks, they are very informative and comprehensive enough to learn things like Data Science and Functional programming in Python.

Top 6 Django Python Courses for Beginners to Learn Online in 2024 [UPDATED]

Hello guys, if you want to become a Python web developer and looking for the best online courses to learn Django, Flask, and Python web development, then you have come to the right place. In the past, I have shared the best Python courses and the best Flask courses, and today, I will share the best course to learn everything about Python web development. You may know that Python is a multi-purpose programming language meaning that you can use it in different fields such as GUI application, artificial intelligence, web application, and much more, just to name a few.

Top 7 Free Maven and Jenkins Online Courses for Java Programmers in 2024 [ UPDATED]

Hello Java programmers,  if you want to learn Maven and Jenkins and look for free resources like free online courses, you have come to the right place. Earlier, I have shared the best Maven courses and best Jenkins courses, and in this article, I will share the best free Jenkins and Maven courses for Java programmers. If you have been doing professional Java development, you know that Maven and Jenkins are two of the most popular tools in the Java world. Maven helps organize your project and provide support to build and deploy Java projects, while Jenkins can provide continuous integration and delivery by completely automating build and deploy projects.

Top 5 Books to Learn Hibernate for Java Developers in 2024 - Best of Lot

Hello guys, if you want to learn Hibernate and looking for the best Hibernate books to start with then you have come to the right place. In the past, I have shared the best Hibernate courses and Spring online courses, and today, I am going to share the best books to learn Hibernate for beginners. These books have been created by Hibernate experts like Gavin King, creator of Hibernate himself and it will help you to master this essential Java framework for full-stack developers. Hibernate is the leading ORM (Object to relational) framework in the Java world used to implement the persistence layer of enterprise Java applications.

Top 5 Books to Improve Coding and Programming Skills - Must Read, Best of Lot

Learning a Programming language, like Java, Python, or C++ is easy, but learning to write good code is not. Writing good code is more Art than Science and also an important differentiating factor between an average programmer vs. a good programmer. Since most of the programmers often look for inspiration and resources to improve their coding skill, I decided to share some of the good books which can help them to improve their coding.  Since many universities, colleges, and training courses only teach programming languages but not the art of coding, it still remains one of the self-learned skills which many programmers acquired either in Job or working on real-world projects.

Top 5 Free AWS Developer Associate Certification DVA-C02 Courses in 2024 - Best of Lot

Hello guys, if you are preparing for the AWS Certified Developer Associate exam and looking for free online courses, then you have come to the right place. In the past, I have shared the free online courses to prepare for AWS Cloud Practitioner and SysOps Administrator certifications. Today, I will share free online training courses to prepare for the prestigious AWS Developer Associate exam. The Exam requires hands-on experience with AWS, but that's not enough, you also need to prepare all the exam topics, and that's where these online courses can help you. These are the best and completely free courses from websites like Udemy, Coursera, freeCodeCamp, and Youtube, and you can use them to prepare for this prestigious AWS cloud certification. 

3 Best Books to Learn Java Programming for Beginners

Hello guys, if you want to learn Java from scratch and looking for the best Java books then you have come to the right place. Earlier, I have shared the free Java courses for beginners, and today, I am going to share the best books to learn Java from scratch. There is no doubt that the best book to learn Java for beginners is indeed Head First Java, 3rd Edition. It's interesting, informative, and yet easy to read, which is what a beginner wants. The only drawback of this book was that there is was 3rd Edition available until a couple of months ago but now that drawback has also gone as the 3rd Edition of Head First Java is now available and it covers Java SE 17, the latest version of Java. 

10 Free Courses to Learn Data Structure and Algorithms in Java, Python, and C++ in 2024 [UPDATED]

Algorithms and Data Structure are two of the most fundamental and essential topics in Computer Science, which is used everywhere in software development. I firmly believe that a good knowledge of these two topics is also crucial to becoming a better programmer because a person who has a good understanding of algorithms and data structures can make thoughtful choices and write programs that can handle changes better and perform well. They are also essential to crack coding interviews at top tech companies like Google, Microsoft, Amazon, Facebook, and Apple, which emphasizes candidates' ability to use existing data structures and algorithms to solve complex problems they have never seen before.

Top 10 Books Every Programmer Should Read

There is a saying that if you learn from your mistakes, you will only going to learn few things, but if you learn from other's mistakes, you can learn a lot of things in a short time, and what could be a better way to learn from someone's experience then reading books. Programming as a career is about constant learning and updating yourself, but unfortunately, there is no right way to begin. Schools and Colleges are far behind when it comes to real-world programming, and every Computer Science graduate is not lucky to work in a company that is great in training. The other viable option is to read books, join online courses, and follow advice from the great programmer and authors who are gone on that path, and learning from the book is the most tried and trusted way of all of them.

Top 5 Books to learn React.js for Beginners in 2024 - Best of Lot

Hello guys, if you want to learn React.js and looking for the best resources like books, online courses, and tutorials then you have come to the right place. Earlier, I have shared the best React courses, websites, roadmap, and projects you can build to learn React.js, and in this article, I am going to share the best books to learn React.js in 2024. From my experience of learning so many techs and programming language, I can say that books are the most complete way to learn. For a better learning experience you can combine those with online courses and projects. For example, you can combine these React books with these best React courses and React projects to become a React Developer in 2024. 

Top 5 Spring Framework Books for Java developers (Includes Spring Security and Spring Boot) - Best of lot

Spring framework is one of the most famous structures in the Java world, which used to develop Java applications, both core Java and web application. It is also one of the most job-oriented skills for Java developers; hence many beginners and intermediate Java programmers try to learn the Spring framework on their own. Though there are some excellent Spring training courses available online, books are still the most popular and preferred way to learn Spring frameworks like Spring core, Spring Boot, Spring MVC, Spring Batch, or Spring Security.  I often receive queries for Spring book recommendations e.g., which Spring book is suitable for beginners, or which Spring book is good for intermediate and advanced developers, which book should I read to learn Spring boot, Spring Cloud, Spring Batch, or Spring security, etc.?

Top 10 Algorithms books Every Programmer Should Read

Algorithms are language agnostic, and any programmer worth their salt should be able to convert them to code in their programming language of choice. Unfortunately, I have come across several programmers who are REALLY good at programming languages like Java or Python, like know minor details of API and language intricacies but have very poor knowledge of the fundamentals of Algorithms and Data Structure. Just ask them to implement any popular sorting algorithms like quicksort or merge sort, and they will fall apart. If you expect them to know more advanced and sophisticated algorithms like String processing algorithms, graph algorithms, tree traversal, or greedy algorithms, be ready to check on Interviews; otherwise, you might end up with some surprises.

Top 10 Java Online Courses and Tutorials for Beginners in 2024 [UPDATED]

Hello everyone! if you want to learn Java Programming and become a Java Programmer in 2024 and looking for the best resources like books, online courses, tutorials, projects, and websites, you have come to the right place. Earlier, I have shared the best Java books for beginners, best Java websites, best Java tutorials, and free Java courses. Today, we will go through some of the best online courses for learning the Java Programming language. These Java online courses are curated from top websites and learning platforms like Coursera, Udemy, Educative, CodeCademy, Javaespecialist, etc. 

Top 5 Free Database and SQL Query Courses for Beginners to Learn Online in 2024 - Best of Lot

Hello guys, I have been sharing some free programming resources e.g. books and courses in this blog for quite some time. Earlier I have shared free courses on Java, Maven, Spring, and Data Structure and Algorithms and today I'll share some of the free online training courses to learn SQL and Database. Why you should learn SQL? Well, it's one of the must-have skills for programmers, application developers, and IT professionals. Like Linux, this is one skill that is going to serve you longer than any other programming language, framework, or library. 

Top 6 Free Courses to Learn TypeScript in 2024 - Best of Lot

If you are interested in learning TypeScript or Angular, one of the popular JavaScript frameworks for developing front-end, which uses TypeScript, and looking for some resources like books, tutorials, and courses, then you have come to the right place. In this article, I am going to share some of the best, free TypeScript online courses you can use to learn this powerful programming language. For those who don't know TypeScript, it's a new dynamically typed programming language from Microsoft that augments JavaScript's programming syntax by adding some new features which help in object-oriented application development, particularly the introduction of Types.

8 Free Linux Courses for Programmers and IT Professionals to Learn Online [2024]

Linux is one of the most popular operating systems to run server-side applications. I have seen almost all Java applications running on Linux, barring a couple of them, which run on Windows as a service. If you take out standalone apps like IDEs or tools, most of the real-world Java applications run on Linux, like payment gateways, trading systems, and other financial applications. That's why it's essential for any programmer, IT professional, or developer to learn and understand Linux, both the operating system, as well as the command line.

Top 5 Free R Programming Courses for Beginners in 2024 - Best of Lot

More and more people are learning the R programming language to become Data scientists, one of the hottest and high-paying technical jobs on the planet. Though I am from Python camp when it comes to choosing between Python and R for Data Science, Machine Learning, and Artificial Intelligence, mainly because of the excellent libraries Python offers, I had tried R for a short time. If you are also in the same boat and want to try or learn R programming for Data Science and machine learning purposes and looking for some excellent free courses to start your journey, then you can take some ideas from this article.

How to replace an element of ArrayList in Java? Example

You can use the set() method of java.util.ArrayList class to replace an existing element of ArrayList in Java. The set(int index, E element) method takes two parameters, the first is the index of an element you want to replace, and the second is the new value you want to insert. You can use this method as long as your ArrayList is not immutable, I mean,  not created using the Collections.unmodifiableList(), in such case the set() method throws java.lang.UnsupportedOperationExcepiton

3 Difference between Web Server vs Application Server vs Servlet Containers - Apache vs JBoss vs Tomcat

In the Java EE, or J2EE or JEE world, there is a lot of confusion between terminology, which is quite evident that now we have three words (J2EE, Java EE, and JEE) to describe the same technology platform. You will see Java developers using the terms like Web Server, Application Server, and Web containers interchangeably but they are not exactly the same. The main difference between a Web server and an application server is that a web server is meant to serve static pages like HTML and CSS, while an Application Server is responsible for generating dynamic content by executing server-side code like JSP, Servlet, or EJB.

What is the difference between byte and char data types in Java? Example

The byte and char are two numeric data types in Java and both can represent integral numbers in a range but there are very different from each other. The main difference between a byte and char data type is that byte is used to store raw binary data while other is used to store characters or text data. You can store character literals into a char variable e.g. char a = 'a'; A character literal is enclosed in single quotes. In terms of range, a byte variable can hold any value from -128 to 127 but a char variable can hold any value between 0 and 255. 

Difference between ArrayList and HashSet in Java? Answer with Example

ArrayList vs HashSet Java
The main difference between ArrayList and HashSet is that one is a List implementation while the other is a Set implementation. It means all the differences between a List data structure and a Set data structure also apply to this pair. For example, List implementations are ordered, it stores the element in the order they were added, while Set implementation doesn't provide such a guarantee. Similarly, since List provides Random access, you can access any element directly if you know the index, but Set doesn't provide such a facility. 

4 ways of Session management in Servlets, JSP, and Java Web Applications

Session tracking or Session management is an important feature of modern web applications which allows the server to remember its clients. By keeping a session for each user, the Server can serve the client better. It also helps in safety, security, and personalization and must for certain kinds of web applications like e-commerce sites like Amazon or e-bay which stores items selected by the user for purchase in a shopping cart, even after the user is logged out. 

String to Enum in Java - Example

Creating Enum from String
You can create Enum from String by using Enum.valueOf() method. valueOf() is a static method that is added on every Enum class during compile-time and it's implicitly available to all Enum along with values(), name(), and cardinal() methods. In order to create Enum from String, String must be the same as declared Enum otherwise, the code will throw "java.lang.IllegalArgumentException: No enum const class". the same technique can be used to convert String into Enum instance as well. 

9 difference between static vs non-static method in Java - Answer

One of the key differences between a static and a non-static method is that the static method belongs to a class while the non-static method belongs to the instance. This means you can call a static method without creating an instance of the class by just using the name of the class like the  Math.random() for creating random numbers in Java. Often utility methods that don't use the member variables of the class are declared static. On the other hand, you need an instance of the class to call a non-static method in Java. You cannot call it without creating an object because they are dependent upon the member variables which have different values for different instances.

How to Add Elements of two Arrays in Java - Example

One of the common programming exercises on various Java courses is the addition and multiplication of two arrays. How do you add two integer arrays in Java? Can you add two String arrays? how about other data types etc? These are some of the interesting questions because Java doesn't support operator overloading. You cannot use the plus operator to add two arrays in Java e.g. if you have two int arrays  a1 and a2, doing a3 = a1 + a2 will give a compile-time error. The only way to add two arrays in Java is to iterate over them and add individual elements and store them into a new array. 

How to read a text file into ArrayList in Java? Examples

Prior to Java 7, reading a text file into an ArrayList involves a lot of boilerplate coding, as you need to read the file line by line and insert each line into an ArrayList, but from Java 7 onward, you can use the utility method Files.readAllLines() to read all lines of a text file into a List. This method returns a List of String that contains all lines of files. Later you can convert this List to ArrayList, LinkedList, or whatever list you want to. Btw, this the fourth article in the series of reading a text file in Java. 

6 Difference between forward() and sendRedirect() in Servlet - Answer

Servlet in JEE platform provides two methods forward() and sendRedirect() to route an HTTP request to another Servlet for processing. Though both are used for forwarding HTTP requests for further processing there are many differences between the forward() and sendRedirect() method e.g. forward is performed internally by Servlet, but the redirection is a two-step process, where Servlet instructs the web browser (client) to go and fetch another URL, which is different from the original. That's why forward() is also known as a server-side redirect and sendRedirect() is known as the client-side redirect. 

java.lang.IllegalStateException: getOutputStream() has already been called for this response

This error comes when you call to include() or forward() method after calling the getOutputStream() from ServletResponse object and writing into it.  This error is similar to java.lang.IllegalStateException: getWriter() has already been called for this response error, which we have seen in the earlier article.

This is the exception:
org.apache.jasper.JasperException: java.lang.IllegalStateException: getOutputStream() has already been called for this response
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:502)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:424)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
HelloServlet.doGet(HelloServlet.java:25)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)

and here is the root cause :

3 ways to Copy a File From One Directory to Another in Java, Examples

Even though Java is considered one of the best feature-rich programming languages, until Java 7, It didn't have any method to copy a file from one directory to another directory. It did have the java.io.File class, which provides a method to check if a file exists or not and methods for several other file operations but it lacks support for copying files from one folder to another. It was easy to write your own routine to copy a file using FileInputStream or FileChannel, most developers prefer to use Apache Commons IO library; which is not a bad idea at all. 

How to read a text file as String in Java? Example

There was no easy way to read a text file as String in Java until JDK 7, which released NIO 2. This API now provides a couple of utility methods that you can use to read the entire file as String e.g. Files.readAllBytes() returns a byte array of the entire text file. You can convert that byte array to String to have a whole text file as String inside your Java program. If you need all lines of files as a List of String e.g. into an ArrayList, you can use Files.readAllLines() method. This returns a List of String, where each String represents a single line of the file. 

How to convert Enum to String in Java with Example

Enum to String Conversion Example in Java
There are two ways to convert an Enum to String in Java, first by using the name() method of Enum which is an implicit method and available to all Enum, and second by using toString() method. name() method of Enum returns the exact same String which is used to declare a particular Enum instance like in WeekDays Enum if we have MONDAY as one Enum instance then the name() will return String "MONDAY". This method of conversion from Enum to String is useful if the String representation of Enum is the same as its String name but if you have different String representation then you can use toString() method. 

How to Increase Heap Size of Java Program running in Eclipse [Example]

It is possible to increase the heap size allocated by the JVM by using command-line options Here we have 3 options

-Xms<size>        to set the initial Java heap size
-Xmx<size>        to set the maximum Java heap size
-Xss<size>          to set the java thread stack size

$ java -Xms1G -Xmx2G MainClass

In the above line, we have set the minimum heap size to 1GB and the maximum heap size to 2GB.

How to fix java.lang.IllegalStateException: getWriter() has already been called for this response [Solution]

This error comes when a Servlet calls the getOutputStream() method on the response object for writing something after calling the include() method. Suppose a Servlet calls the include() method to load the response of a JSP. Since JSP has already written the response on it hence again opening OutputStream on the response object is illegal, you get the java.lang.IllegalStateException: getWriter() has already been called for this response error. This error also comes when you try to include the response of another Servlet and then tries to write something on the output stream again. In short, your Servlet should never write anything on the response object after calling the include() method. 

Difference between jsp:include and jsp:forward action- Example

JSP provides standard actions to do things without using Java inside the scriptlet. Two of such standard actions, which help JSP to interact with other server resources e.g. another JSP, Servlet, or HTML files are, include and forward actions. The <jsp:forward> action enables you to forward an HTTP request to a static HTML file, a servlet, or another JSP. It has an attribute called page, which accepts the URL of another resource as shown below:
<jsp:forward page="URL" /> 

How to get Current Date and Time in Java with Example

You can get today's date or current date and time in Java by creating a new Date() object. A java.util.Date object represents the current date and time instance in Java. Now, if you want to date in DDMMYYYY format or any other date format, you can easily convert the Date object to String by using SimpleDateFormat class. Since the Date instance contains both date and time, if you only need a date then you can further convert the java.util.Date to java.sql.Date. Similarly, if you need just time then you can convert the java.util.Date to java.sql.Time, they represent the date and time part of java.util.Date object in Java. 

How to convert java.util.Date to java.sql.Timestamp in Java - JDBC Example

You can convert java.util.Date to java.sql.Timestamp by first taking the long millisecond value using the getTime() method of Date class and then pass that value to the constructor of Timestamp object. Yes, it's as simple as that. For better code reusability and maintenance, you can create a DateUtils or MappingUtils class to keep these kinds of utility or mapping functions. Now, the question comes, why do you need to convert java.util.Date to java.sql.Timestamp? 

Well, If you are storing date values to a database using JDBC, you need to convert a java.util.Date to its equivalent java.sql.Timestamp value. Even though both of them represent date + time value and can be stored in DATETIME SQL type in Microsoft SQL Server database or equivalent in other databases like Oracle or MySQL, there is no method in JDBC API which takes the java.util.Date object. Instead, you have got three separate methods to set DATE, TIME, and TIMESTAMP in the java.sql package.

How to Run a JAR file from Command Prompt - Windows and UNIX [Example]

So you got a JAR file that contains your favorite Java game and you are wondering how to run a Java program from a JAR  file? Or you may be simply trying your hand after running the Java program from the command prompt and Eclipse IDE. Anyway, it's good to know How to execute Java programs from the JAR file, as the JAR file is the most popular way of shipping Java programs. JAR file usually contains all sources and resources in the form of class files, images, sound files, etc. 

What is default Serialization in Java? Serializable and Externalizable Interface Explanation

What is Serialization in Java
Serialization in Java is a process to persist any Java Object's state into a File System or convert them into a byte stream to transfer over the network to another JVM or program. Serialization in Java is done by JVM by employing the default Serialization process which persists all of the Object's state except the transient variable and a static variable. How Serialization works in Java is another popular Java Serialization interview question, well It's easy to make any Java class Serializable, the class needs to implements java.io.Serializable interface, and JVM will automatically serialize its instance when passed over to java.io.ObjectOutputStream using writeObject()

How to use Enum in Java? Example

Enum is a useful feature of Java and the best way to represent a fixed number of things like the number of the planet in the solar system, the number of state orders can be, or simply a number of days in a week. Java Enum is different than its predecessor in other languages like C and C++, where the enum is just a wrapper around integer constant. Enum in Java is a full-blown type like class and interface, they can have a constructor (though only private constructors are permitted for Enum), they can override methods, they can have member variables, they can even declare methods, can implement interfaces, and have specialized high-performance Map and Set implementation in form of EnumMap and EnumSet.

Why you shouldn't use == with float and double in Java?

In this article, you are going to learn why you shouldn't use == with float and double in Java? Especially for checking loop termination conditions. Java programmers often make the mistake of using floating-point numbers in a loop and checking conditions with the == operator, in the worst case this could create an infinite loop, causing your Java application to hung.

For example, the following code will not work as you expect :

for(double balance = 10; balance!=0; balance-=0.1) {
   System.out.println(balance);
}

How to load data from CSV file in Java - Example

You can load data from a CSV file in a Java program by using BufferedReader class from the java.io package. You can read the file line by line and convert each line into an object representing that data. Actually, there are a couple of ways to read or parse CSV files in Java e.g. you can use a third-party library like Apache commons CSV or you can use Scanner class, but in this example, we will use the traditional way of loading CSV files using BufferedReader.

6 Difference between include directive and include action in JSP

Difference between include directive and include action
Even though both include directive and include action allows you to include the response of one JSP into another, they are quite different from each other e.g. include directive is processed at translation time and used to include the static resources e.g. HTML files, images, and CSS, etc, while the <jsp:include> action is processed at request time and used to include more dynamic resources e.g. JSP or Servlet. What is the difference between include directive and include action is also one of the most popular JSP interview questions, mostly asked either at telephonic round or first few round of Java web developer interviews?

Top 5 Free Courses to Learn C Programming for Beginners in 2024 - Best of Lot

Hello guys, if you want to learn the C Programming language and looking for a free online course then you have come to the right place. In the past, I have shared the best C programming courses and top C++ courses and today I am going to share the best free C programming courses for beginners.  C is one of the most extended programming languages in the world. It is used for creating operating systems and embedded applications. With the increasing popularity of object-oriented programming, C is being rapidly replaced as "the" programming language by C++, a superset of the C language that uses an entirely different set of programming concepts, but the base is the same in both.

Top 5 Python Books for Beginners to Learn Programming in 2024 - Best of Lot

Python is one of the most popular programming languages, and there is a vast demand for Programmers who knows Python, and the best part is its increasing every year. If you want to learn Python in 2024 then you have come to the right place because earlier I have shared some of the free courses to learn Python and today I am going to share some of the best books to learn Python in 2024. Even though I am a Java Programmer, I am learning Python. In the real world, you often find that a big project in a bank or insurance domain leveraging several technologies together, like Java, C++, Python, UNIX, SQL, and several others.

Thread-safe Singleton in Java using Double Checked Locking Idiom

Singleton Pattern is one of the famous design patterns from the Gang of Four. Even though nowadays it is considered as an anti-pattern, it has served us well in the past. In the Singleton pattern, a class has just one instance throughout its lifetime and that instance is shared between multiple clients. Singleton class has two responsibilities, first to ensure that only instance of the class gets created and second, to provide a method getInstance() so that everyone can get access to that single instance, I mean,  global access.

How to convert float to int in Java? Examples

Even though both float and int are 32-bit wide data types, the float has a higher range than the integer primitive value. Since a float is bigger than int, you can convert a float to an int by simply down-casting it e.g. (int) 4.0f will give you integer 4. By the way, you must remember that typecasting just get rid of anything after the decimal point, they don't perform any rounding or flooring operation on the value. So if your float value is 3.999, down casting to an integer will produce 3, not 4. If you need rounding then consider using the Math.round() method, which converts float to its nearest integer by adding +0.5 and then truncating it. 

How to use BigInteger class in Java? Large Factorial Example

In Java, the BigInteger class, part of the java.math package, provides a powerful and flexible solution for dealing with arbitrarily large integers that exceed the capacity of primitive data types like int or long. This class is particularly useful when precision and magnitude are crucial, such as in cryptographic applications, mathematical computations, or scenarios where large integers are involved. Unlike primitive data types, BigInteger can handle numbers of virtually unlimited size, making it an essential tool for developers facing challenges related to integer overflow or the need for extensive precision. In this guide, we will explore the fundamentals of using the BigInteger class, covering instantiation, basic arithmetic operations, conversion, and the practical scenarios where its usage becomes indispensable. You will also understand the capabilities of BigInteger empowers developers to tackle numerical challenges with confidence in Java applications. For example, we will use BigInteger to calculate factorial of large number.

How to set JAVA_HOME (PATH) in Mac OS? Example Tutorial

You can set JAVA_HOME in Mac OS X 10,10 or Yosemite by adding the following command in your ~/.bash_profile file, as shown below:

export JAVA_HOME=`/usr/libexec/java_home` (remember backticks)
or
echo export "JAVA_HOME=\$(/usr/libexec/java_home -v 1.7)" >> ~/.bash_profile

This will append export "JAVA_HOME=\$(/usr/libexec/java_home -v 1.7)" into your bash_profile file. If you have set JAVA_HOME in UNIX then it's exactly similar to that.

How to use final in Java? Final class, final method, and final variables Example

You can use the final keyword with variables, methods, and classes in Java. You can use the final modifier with variables to make them constant. A final variable is initialized only once in its lifetime, once initialized you cannot change its value. Though you can initialize the final variable at the time you declare them or you can initialize them at constructor if they are blank final variables. A static final variable, also known as a constant must be initialized in the same line. You can also use the final modifier with methods to prevent method overriding. In Java, you cannot override final methods. 

How to write to File in Java using BufferedWriter [Example]

You can use either OutputStream or Writer class in Java to write data to a file in Java. For example, you can use a combination of FileWriter and BufferedWriter to write text content into a text file in Java. If you want to write raw bytes consider using FileOutputStream class. Just remember that InputStream is used to read data and OutputStream is used to write data to file or socket. You can write anything to file e.g. String, integer, float values, etc. Java provides DataOutputStream to write different data types directly into a file like writeInt() to write integer values, writeFloat() to write floating-point values into a file, and writeUTF() to write String into File.  BufferedWriter, like its counterpart BufferedReader, allows you to perform buffered IO, which can drastically improve performance while reading large files.