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How to parse String to LocalDate in Java 8 - DateTimeFormatter Example

From Java 8 onward, you are no longer dependent on the buggy and bulky SimpleDateFormat class to parse and format date Strings into real Date object in Java e.g. java.util.Date. You can use the DateTimeFormatter class from java.time package for all your formatting and parsing need. You are also no longer required to use another buggy class java.util.Date if you are doing fresh development, but if you have to support legacy code then you can also easily convert LocalDate and LocalTime to java.util.Date or java.sql.Date. In this tutorial, we will learn about both parsing String to date in Java and formatting Date into String.

10 Free Java 8 Certification Sample Questions - OCAJP8 and OCPJP8 - 1Z0-808 and 1Z09 dumps

If you are preparing for Oracle Java SE 8 Certifications e.g. OCAJP8 and OCJP8, also known as exam 1Z0-808 and 1Z0-809 and looking for some free practice tests then you have come to the right place. In this article, I am going to share some of the best OCAJP 8 and OCPJP 8 mock tests available for free of cost online, so that you can check your speed and accuracy before the real exam. These tests are not just useful for Oracle's Java OCA and OCP certification but also for upgrade exams like OCJP 8 upgrade exams with code 1Z0-810 and 1Z0-813, upgrade to Java SE 8 from Java 6 and prior version. Many of these practice tests are like web simulator where you need to solve a relatively small number of questions within 45 to 60 minutes. The web simulator also includes timer so that you can finish these free mock tests on time.

How to convert Integer to String in Java - Example

This is the second part of String to Integer data type conversion tutorial in Java, in the first part you have learned how to convert String to Integer and in this article, you will learn the opposite i.e. convert from Integer to String. Actually, you can apply all the tricks, which I had told you before about converting long to String, and autoboxing will take care of converting int to Integer in Java. But, if you care for performance and believe in not using auto-boxing when not needed then there are still a couple of ways which directly converts an Integer object to String e.g. Integer.toString() method, which returns a String object and doesn't have any auto-boxing overhead. Let's see a couple of more ways to convert an Integer to String in Java.

10 Books Java Developers Should Read in 2019 - Best Of Lot

Hello guys, If you are Java developer and wondering what to read in 2019 then you have come to the right place. In this article, I am going to share 10 books on Java, Spring, and related technology a Java developer can read. I have included books for both experienced Java developer who is more inclined to learn about architecture stuff,  developing for Cloud, MicroService, Java 9, and Spring 5 features and thinking of learning Kotlin to improve their productivity, but I have not forgotten to junior and less experienced Java developers or some who are thinking to start their journey into Java world in 2019.

5 Things You can Gift to Programmers,Software Developers and Tech Geeks

So, its that time of the year again when you start thinking about gifts for your programmer boyfriend, husband, colleagues or your near dear ones. Even if selecting gifts were not tough, if your friend happened to be a programmer, it becomes slightly tougher. You might have heard that Programmers are aloof, nerd and tech freaks, well, you heard it right. Programmers  prefers to be alone in their own world but they also like gifts and you got it right, they are a nerd so they like books, gadgets, music and something which help them to learn something e.g. a PluralSight membership.

In 2017, gadgets like Apple Watch and Samsung Gear is rocking but that's what everyone is buying so if you want to be a little bit different, chose the one from this list.

5 Free Linux Courses for Programmers and IT Professionals to Learn Online

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 runs on Windows as service. If you take out standalone apps like IDEs or tools, most of the real world Java applications run on Linux e.g. payment gateways, trading systems, and other financial applications. That's why it's very important for any programmer, IT professional, or a developer to learn and understand Linux, both operating system, as well as command line.

3 Books to learn Java Programming from Scratch in 2019 - Best of Lot Must Read

I receive half a dozen emails every day asking about which is the best to learn Java from scratch? Which book should I read in 2019 to learn Java? or Which is the best Java for beginners? When I receive such email, before giving my recommendation I ask two questions, first do you have any programming experience? e.g. Are you coming from C, C++ or Python background? Or you are a fresher with no experience in programming, just a couple of classes on data structure and algorithm and operating system on college. If the guy some prior experience I recommend him the book like Core Java for the Impatient which teaches basics of Java programming language and API and also how to use Java in right way.

Top 5 Amazing Gifts for Programmers, Coders, and Software Developers

If you are planning for a surprise gift to your programmer boyfriend and husband on this holiday season e.g. Black Friday, on Christmas, or New Year or maybe on his next birthday, but not sure what to gift, then you have come to the right place. In this article, I am going to share some of the best gifts every programmer wish for. To be honest with you, buying a gift is easy but finding the right gift is very tough. I have spent countless hours on the internet to find a perfect gift for one of my colleague's husband and this article is a result of that research. The general perception of programmers is that they are a nerd, they love books, gadgets, cool stuff, music, but the perfect gift is something which not only provides the enjoyment but also the value.

Java 8 compute() and computeIfPresent() Example

The JDK 8 has added several useful methods in existing interfaces e.g. java.util.Map, java.util.Collection, and java.util.concurrent.ConcurrentMap. Thanks to default methods, the much-needed evolution of existing interfaces become possible. Out of many useful methods, one method which stands out to me is the compute() method, which allows you to update a value in ConcurrentHashMap atomically. As per Java documentation, The compute() function tries to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping). The entire function is performed atomically.

10 ways to learn a New Technology, Programming language, Frameworks, or Libraries in 2019

One of the main challenges of being a programmer or software engineer is the constant learning. Yes, that's true. As a programmer or developer, we always need to learn new things, sometimes every year. Thanks to C, Java, Linux, and SQL, we still have some ground but the way these technologies are used changes every year. For example, we have a new JDK 9 release in 2017, even though many Java developers are still learning Java 8. We also have a Spring Framework 5.0 release in 2017, combined with Spring Security 5.0 and Spring Boot 2.0 release, which many of us need to learn in 2018.

10 Examples of Collectors and Stream in Java 8

As the name suggests, Collectors class is used to collect elements of a Stream into Collection. It acts as a bridge between Stream and Collection and you can use it to convert a Stream into different types of Collections e.g. List, Set, Map. Btw, it not just limited to that, it even provides functionalities to join String, group by, partition by and several other reduction operators to return a meaningful result. It's often used along with collect() method of Stream class which accepts a Collectors. In this article, we'll learn Collectors by following some hands-on examples.

How to Send HTTP Request from Java Program - Example Tutorial

If you are thinking is it possible to send an HTTP request from a Java program and if yes, how to send a simple HTTP GET request in Java, then you have come to the right place. In this article, I'll show you how you can use the HttpURLConnection class from java.net package to send a simple HTTP request in Java. But, first let me answer your first question, is it possible to send HTTP request in Java? Yes, it's possible and you can send any kind of HTTP request e.g. GET, POST, PUT, DELETE, HEAD, or PATCH. The java.net package provides a class called HttpURLConnection, which can be used to send any kind of HTTP or HTTPS request from Java program.

How to Set Specific Java Version for Maven in Windows?

Maven is a great build tool and most of the Java developer uses Maven to build their projects, but like any other tool, there are some intricacies which you need to know while using it. One of them is that Maven uses Java version from the JAVA_HOME environment variable and not the PATH environment variable. If you have multiple JDK installed on your machine and getting an Unsupported major.minor version 51.0 or Unsupported major.minor version 52.0 error while building your project but have right Java version in PATH then you may need to check the JAVA_HOME and update it. If you don't have access to do it then you can still change JAVA_HOME using set command in your local shell and run the Maven's mvn command to build the project

5 Difference between BufferedReader and Scanner class in Java - File Tutorial Example

Hello guys, welcome to my blog. Today, we'll discuss another interesting Java interview questions, BufferedReader vs Scanner. It's not only important from interview point of view but also to work efficiently with Java. Even though both BufferedReader and Scanner can read a file or user input from the command prompt in Java, there some significant differences between them. One of the main difference between BufferedReader and Scanner class is that former class is meant to just read String or text data while Scanner class is meant to both read and parse text data into Java primitive types like int, short, float, double, and long.

Difference between final vs finally and finalize in Java? Answer

The final, finally, and finalize are one of the three confusing keywords, modifiers and methods in Java. They sound similar but they are for different purpose. For example, the final keyword is a modifier in Java. When you use the final keyword with a class it becomes a final class and no one can extend this e.g. String is final in Java. When you use the final modifier with method than it cannot be overridden in a subclass, and when you use the final keyword with a variable, it becomes a constant i.e. its value cannot be changed once assigned. On the other hand, finally is a keyword related to exception handling in Java. It's often used with try block and it's part of try, catch and finally trio.

How to add/remove new elements to an array in Java?

Java beginners often ask how to add new elements to an array? or how to remove elements from an array in Java? is that possible in Java? Well, no, it's not possible in Java because arrays length cannot be changed once created. Which means neither you can add new elements nor you can remove an old one. All you can do is that reassign values to the different bucket. For example, if you have a String array of length 3 e.g. {"java", "is", "great"} then you can just replace the individual index to make it like {"Python", "is", "great"} by replace "java" with "Python" at first index, but you cannot add or remove elements.

How to Print all leaf Nodes of a Binary tree in Java - Coding Interview Questions

This is another interesting coding problem which is based on a binary tree and mostly asked beginner programmers. If you have some experience in solving binary tree based problems then it's rather easy to solve because, like many other binary tree algorithms, you can use recursion to print all leaf nodes of a binary tree in Java. Since the tree is a recursive data structure, you can apply the same algorithm to both the left and right subtree. In order to solve this problem, the first thing you should know is what is a leaf node because if you don't know that then you won't be able to solve the problem. Well, a leaf node is the one who's left and right child nodes are null.

How to Reverse a String in place in Java - Example

One of the common Java coding interview questions is to write a program to reverse a String in place in Java, without using additional memory. You cannot use any library classes or methods like e.g. StringBuilder to solve this problem. This restriction is placed because StringBuilder and StringBuffer class define a reverse() method which can easily reverse the given String. Since the main objective of this question is to test the programming skill and coding logic of candidate, there is no point giving him the option to use the library method which can make this question trivial. Now, how do you solve this problem? If you are familiar with array data structure then it would be easy for you. Since String is backed by a character array, you can use the same in place algorithm we have used to reverse an array in place.

How to use ConcurrentHashSet from ConcurrentHashMap in Java 8 - Example Tutorial

There is no ConcurrentHashSet in JDK 8 but you can still create one for yourself by using the ConcurrentHashMap class of java.util.concurrent package. There is a new method added into ConcurrentHashMap in JDK 8, newKeySet(), which allows you to create a concurrent hash set backed by a concurrent hash map. If you remember whenever you get keys from the map they are returned in a Set e.g. for the old keySet() method because map only has unique keys. Since map doesn't allow duplicate keys, it can be used as a set, as long as you only care for keys or just one element. That's why Java designers are added newKeySet() method to convert a map to set. This is also a static method, which means you don't need a ConcurrentHashMap object to create a concurrent hash set.

3 Examples to Generate Random Integers on a Range in Java

Manytimes you need to generate random numbers, particular integers in a range but unfortunately, JDK doesn't provide a simple method like nextIntegerBetween(int minInclusive, int maxExclusive), because of that many Java progarmmers, particularly beginners struggle to generate random numbers between a range e.g. random integers between 1 to 6 if you are creating a game of dice, or random number between 1 to 52 if you are creating a game of playing cards and you need to choose a random card, or most commonly random numbers between 1 to 10 and 1 to 100. Then, the question comes, how to solve this problem? How to generate random int values between a range? Well, you need to do a little bit of work.

How to Convert a List into Map in Java 8 - Example Tutorial

One of the common tasks in Java programming is to convert a list to map and I have written about this in past and today we'll see how Java 8 makes this task easier. Btw, be it Java 7 or Java 8, you need to keep something in mind while converting a list to map because they are two different data structure. For example, the list allows duplicate elements but keys in a map must be unique, the value can be duplicated but a duplicate key may cause a problem in Java 8. Similarly, another concern is order. A list is an ordered collection but the map doesn't guarantee any order unless you decide to use LinkedHashMap, which keeps insertion order or TreeMap which keeps mapping in the sorted order of keys. This is one of the important details which many Java beginners forget and then spend hours to chase subtle bugs.

Top 10 Java 8 Tutorials and Courses - Best of Lot, Must Read

It's almost six months since Java 8 was released and there are so many Java 8 tutorials are written by Oracle, bloggers, and other peoples, but which should you read? Which tutorials are worth of your time? Actually, this question is asked to me by one of my reader called John, he was asking me about some good Java 8 tutorials, which he can read to start with. This encouraged me to take a look at some of the Java 8 tutorials available on the internet and form a list of best. I have just used three criterion, content, language and length. Because tutorials complement books, they should not be like the book. They should be small enough to complete in few hours and complete enough to give useful information. I also like tutorials, which discusses practical problems and examples.

How to Convert a LinkedList to an Array in Java? Example

You can convert a LinkedList to an array in Java by using the toArray() method of the java.util.LinkedList class. The toArray() method accepts an array of relevant type to store contents of LinkedList. It stores the elements in the array in the same order they are currently inside the LinkedList. By using the toArray() method you can convert any type of LinkedList e.g. Integer, String or Float to any type of Array, only catch is this you cannot convert a LinkedList to an array of primitives i.e. a LinkedList of Integer cannot be converted into an array of ints by using toArray() method, but you can convert it to array of Integer objects, that's perfectly Ok.

5 ways to Compare String Objects in Java - Example Tutorial

here are many ways to compare String in Java e.g. you can use equals() and equalsIgnoreCase() for equality check and compare() and compareTo() for ordering comparison. You can even use the equality operator == to perform reference based comparison e.g. to check both the String reference variable points to the same object. In general, equals() is used to check whether the value of given String is same i.e. they contain same characters in the same sequence or not e.g. "Groovy".equals("Groovy") will be true if you compare them using equals() method. You can also use equalsIgnoreCase() to check if they are equal irrespective of case e.g. "Apple" and "apple" will be same if you compare them using equalsIgnoreCase() method.

How to Count number of 1s (Set Bits) in Given Bit Sequence in Java

Good morning folks, In today's article, we are going to discuss one of the frequently asked bit manipulation based interview question, how do you count the number of set bits in given bit sequence?  Bit Manipulation is an important topic on programming interview and a good programmer should have sufficient knowledge and skill to work with binary numbers. This kind of questions tests that skill of the programmer. Sometimes, it is also asked as for how to count the number of 1s (ones) in given number? Both are the same question because 1 is also known as set bit.  For example, if given input is 1000110010 than your program should return 4, as three are only four set bits in this bit sequence.

Can you Make a Class Static in Java? Interview Question

This is one of the tricky questions in Java because there is no straight forward Yes and No answer here. You cannot make a top level class static in Java but Yes, you can make a nested class static in Java. In fact, it is even advised (see Effective Java) to prefer a nested static class in Java than normal inner classes. Now, the question comes what is a top level class and what is a nested class in Java? Well, you can declare multiple classes in a single Java source file. A class is said to be top level if it is not inside any other class and a class which is inside another class is known as nested class. You can create nested class inside another top level or another nested class in Java. This is the class which can be static in Java.

Top 20 Hibernate Interview Questions for Java J2EE Programmers

Hibernate is one of the most popular persistent frameworks in Java world. Hibernate offers object to relational (ORM) solution which frees Java developers from writing tedious, hard to read and cluttered JDBC code converting SQL columns into Object properties. Apart from freeing Java developer from writing JDBC and database interaction code, Hibernate also offers the out-of-box solution on caching, proxying and lazy loading which drastically improves the performance of your Java Web application. Given it's important in Java Web application development field Hibernate has become of one of the most sought-after skill and goes hand in hand with Spring framework. That's why Spring and Hibernate interview questions are also very popular in Java interviews, particularly for web development positions.

JDBC - Difference between PreparedStatement and Statement in Java

If you have worked with database interfacing with Java using JDBC API then you may know that the JDBC API provides three types of Statement for wrapping an SQL query and sending for execution to the database, they are aptly named as Statement, PreparedStatement, and CallableStatement. First one, Statement is used to execute normal SQL queries e.g. select count(*) from Courses. You can also use it to execute DDL, DML and DCL SQL statements. The second one, PreparedStatement is specialized to execute parameterized queries e.g. select * from Courses where courseId=?, you can execute this SQL multiple times by just changing the course parameters. They are compiled and cached at database end, hence quite fast for repeated execution.

Difference between ISNULL and COALESCE T-SQL Function in Microsoft SQL Server - Interview Questions

Even though both ISNULL() and COALESCE() function provides alternate values to NULL in T-SQL and Microsoft SQL Server e.g. replacing NULL values with empty String, there are some key differences between them, which is often the topic of SQL Server interview. In this article, you will not only learn the answer to this question but also learn how to use COALESCE and ISNULL function properly. One the main difference between them is that  COALESCE() is a standard SQL function but ISNULL() is a Microsoft SQL Server specific, which means it's not guaranteed to be supported by other database vendors like Oracle, MySQL or PostgreSQL.

How to Convert a Comma Separated String to an ArrayList in Java - Example Tutorial

Suppose you have a comma-separated list of String e.g. "Samsung, Apple, Sony, Google, Microsoft, Amazon" and you want to convert it into an ArrayList containing all String elements e.g. Samsung, Apple, Google etc. How do you do that? Well, Java doesn't provide any such constructor or factory method to create ArrayList from delimited String, but you can use String.split() method and Arrays.asList() method together to create an ArrayList from any delimited String, not just comma separated one. All you need to do is first split the given String on delimiter e.g. comma using the split() method, this will give you an array of String. Now, you can pass that array to Arrays.asList() method to create a List, but remember this would be fixed length list and not truly an ArrayList.

Java Enum With Constructor Example

Java Enum with Constructor
Many Java developers don't know that Java Enum can have a constructor to pass data while creating Enum constants. This feature allows you to associate related data together. One example of passing arguments to enum Constructor is our TrafficLight Enum where we pass action to each Enum instance e.g. GREEN is associate with go, RED is associated with stop and ORANGE is associated with the slow down. This is really useful because it provides more context and meaning to your code. If you want, you can also provide one or more constructor to your Enum as it also supports constructor overloading like normal Java classes. This is very different from enum you have seen in C or C++, which is just a collection of fixed thing without any OOP power.

How to Implement a Power Function in Java - Coding Interview Problems

Even though the Java library has a power function, Math.pow() to calculate the power of a given number in Java, it's a common programming exercise for Java programmer to implement a power function. If you have used the Math class then you know that the java.lang.Math.pow(double a, double b) returns the value of the first number raised to the power of the second number and you need to do the same. In other words, you need to write a Java function to calculate the power of integer numbers for simplicity. The original method accepts a double value but you are allowed to use just integer but beware that power function may overflow.

Effective Java 3rd Edition by Joshua Bloch – A Must Read Book for Java Developers

Hello guys, you might have heard about it that Effective Java 3rd Edition is finally available. After 10 years of the long wait by Java programmers from all over the world, finally, an updated version of, probably the most popular Java book on the planet is released now. This new version covers the features and paradigm introduced in JDK 7, 8, and 9.  Joshua Bloch has done a great job in also updating most of the items to keep it relevant to the newer version. Apart from that, there is a whole new chapter added to explain best practices around Java 8 features. I know you don't need any reason to read this book, given its huge popularity and acceptance. Many startups which use Java,  particularly in India, are also distributing copies of this book as a New Year Gift.

Java 8 Default Methods FAQ - Frequently asked Questions and Answers

In last a couple of articles, I have to talk about default methods introduced in JDK 8. First, we have learned what is default method and why it is introduced in Java. Then we have seen the example of how you can use default methods to evolve your interface. After that we have analyzed does Java really support multiple inheritances now in JDK 8 (see here) and how will Java handle the diamond problem that will arise due to default methods. For example, what will happen if a class extend a class and implement an interface and both contain a concrete method with same method signature? Will a diamond problem arise? How will Java handle that and how you can solve it, and the difference between abstract class and interface in Java 8?  Once you went through those articles, you would have a good knowledge of default methods in Java 8.

Difference between wait() and join method in Java thread

Though both wait() and join() methods are used to pause the current thread and have a lot of similarities they have different purposes. One of the most obvious differences between the wait() and join() method is that former is declared in java.lang.Object class while join() is declared in java.lang.Thread class. This means that wait() is related to the monitor lock which is held by each instance of an object and join method is related to Thread itself. The wait() method is used in conjunction with notify() and notifyAll() method for inter-thread communication, but join() is used in Java multi-threading to wait until one thread finishes its execution.

A Beginners Guide to Package in Java

If you are learning Java then you might have come across package concept and if you are wondering what is package and why should we use it then you have come to the right place. In this article, I will explain what is package in Java and other stuff around the package, including some best practices which using the package in Java. In the simplest form, a package is a way to organize related functionality or code in single place in Java. If you look from File System perspective then a package in Java just represent a directory where Java source file is stored in compilation and class files are stored after compilation. For example, if you create a class HelloWorld in a package called com.java67.welcome; then it will reside under directory com/java67/welcome in the source tree and you can view that in your IDE like Eclipse or Netbeans or even by navigating to file system.

Java CountDownLatch Example - Multithreading and Concurrency Tutorial

The CountDownLatch is an important concurrency utility class which was added in JDK 1.5 but unfortunately, many Java developers still struggle to understand and use this powerful tool. You can use CountDownLatch if you are spawning multiple threads to do different jobs and want to know when exactly all tasks are finished so that you can move to next stage. In other words, you can block a thread until other threads complete their task. One of the good examples where you can use CountDownLatch is an application which downloads data from a database or another application. For example, we are creating a Java program to download all Udemy courses. Since Udemy has thousands of courses, you create different threads to download different categories e.g. technology, development etc.

How to work with Files and Directories in Java

The File API is one of the important parts of any programming language or API and even though Java's file API both new and old, are powerful, they are not intuitive enough compared to other languages e.g. Python. Apart from knowing the essential classes and abstractions e.g. File, InputStream, OutputStream, Reader, Writer, Channel etc, you also need to know and remember some nitty gritty detail to avoid subtle issues. There are many articles out there on the internet which can teach you how to read and write data from the file but there are very few which will tell you to do it in right way.

How to implement Radix Sort in Java - Algorithm Example

The radix sort, like counting sort and bucket sort, is an integer based algorithm (i.e. the values of the input array are assumed to be integers). Hence radix sort is among the fastest sorting algorithms around, in theory. It is also one of the few O(n) sorting algorithm along with a bucket and counting sort. The particular distinction for radix sort is that it creates a bucket for each cipher (i.e. digit); as such, similar to bucket sort, each bucket in radix sort must be a growable list that may admit different keys.

How to convert primitive int value to a Long object in Java?

Suppose you have an int variable but the part of the application is expecting a Long object, how do you convert a primitive int to a Long object in Java? It shouldn't be a problem, right? after all long is a bigger data type than int, so all int values are acceptable as long, but we also need a Long object, not just the long primitive value. Now, the problem is reduced to converting a long primitive to Long object, which is not really a problem if you are running on JRE version higher than Java 5. But, sometimes autoboxing is not efficient e.g. when you have to convert multiple long values into the Long object in a loop. A better way to convert your long primitive to the Long object is by using static factory methods like Long.valueOf(long l), which was originally meant to convert long primitive values to a Long object, prior to Java 5, but, also works fine with int primitive.

Difference between OCAJP7 and OCAJP8 Certification - 1Z0-803 vs 1Z0-809

One of the frequently asked questions asked by most of the OCAJP certification candidates is, what are the differences between OCAJP 8 and OCAJP 7? And,  Which one Java developers should go for in 2018? OCAJP7 or OCAJP8? The obvious answer to this question is the latest Java version of the exam i.e. OCAJP 8. Since it's already more than 5 months since Java 9 is out but there is no OCAJP 9 certification, the OCAJP 8 should be the exam, Java developer should pursue in 2018. The question is more for those who are looking to become certified Java developer in quick time and doesn't know Java 8 yet e.g. experienced Java developers who have extensively worked in Java SE 6 and prior version but don't have any Java certification yet.

Java 8 Stream findFirst() and filter() Example

Suppose, you have a list of prime numbers and you need to find the first prime number which is greater than a given number? How do you find it? Don't tell that you will loop through the list and check each element and return the first element which is greater than the given number. Well, that's right but that's not what you should do in Java 8. That's good for Java 7 or earlier version but Java 8 offers you many better alternatives and one of them is Stream. You can use the Stream class along with filter() and findFirst() methods to find out an element based upon a Predicate, a functional interface for defining a condition which returns a boolean.

Top 15 Spring Boot Interview Questions with Answers for Java/JEE Programmers

Hello guys, if you are preparing for your next Java interview and Job description mentioned about Spring framework, then you should also prepare some Spring Boot interview questions to avoid disappointment. The Spring Boot is now the standard way to use Spring framework for Java development and almost all the companies are moving from the traditional way of using Spring Framework to more modern Spring Boot way. Gone are the days, where questions like have you used Spring Boot was asked to the developer. Nowadays interview expects more knowledge of Spring Boot from candidates and there are reasons for it, which we'll explore in this article.

Top 20 Essential Java Interview Questions with Answers for Freshers with 1 to 2 years Experienced

If you are grad looking for an internship position in a company which uses Java, or a fresher, just out from college and looking out for Java development position, then this post is for you. I have attended, taken and participated in a different level of Java interviews, and I can say there is a huge difference between them, which is not surprising because you obviously want to ask different level questions based upon whether the candidate is fresher or experienced. Similarly, the question at phone interview, written test, and face to face interviews, keeping this in mind, and give you always have a limited amount of time before going for an interview, It's important to prepare right set of questions.

Binary tree InOrder traversal in Java using Recursion

The InOrder traversal is one of the three popular ways to traverse a binary tree data structure, other two being the preOrder and postOrder. During the in order traversal algorithm, left subtree is explored first, followed by root, and finally nodes on right subtree. You start traversal from root then goes to left node, then again goes to left node until you reach a leaf node. At that point in time, you print the value of the node or mark it visited and moves to right subtree. Continuing the same algorithm until all nodes of the binary tree are visited. The InOrder traversal is also known as left-node-right or left-root-right traversal or LNR traversal algorithm.

Top 35 Java String Interview Questions with Answers

The  String class and concept is a very important class in Java. There is not a single Java program out there which is not using String objects and that's why it's very important from interview point of view as well. In this article, I am going to share 35 String based questions from different Java interviews. It includes questions on java.lang.String class as well as string as data structure e.g. some coding questions something like I have shared in my earlier article about 75 Coding questions to Crack any Programming Job interviews.  You can use this list to refresh your knowledge about String in Java as well as to prepare for your next Java interview. If you have any good String questions which are not on this list, feel free to drop a note and I'll include in this list.

Top 5 Books to Learn Grails Framework for Java and Groovy Developers.

Earlier, I have shared some of the must-read Groovy books and today, I'll share some of the best books to learn Grails for Java developers. Grails is a web application development framework completely written in Groovy. The Grails and Gradle framework are built using Groovy language. Grails is the framework to develop a web application using Groovy. The concepts within Grails, like interceptors, tag libs, and Groovy Server Pages (GSP) are very similar to what we have in Java. You'll be amazed at how quickly you can have a first-class web application up and running from ground zero. Grails includes everything you need in a single zip file on a web server (Jetty), a database (HSQLDB), Spring, Hibernate, even a Groovy version of Ant called GANT.

3 Ways to Convert String to Short in Java - Example Tutorial

In last a couple of examples, I have taught you how to convert String to Integer, Long, Double, Float, Boolean, and Byte in Java and today I will show you how to convert String to Short in Java, but before that let's revise what is short data type in Java. The short is an integral data type similar to the int but it only takes 2 bytes to store data as compared to 4 bytes required by an int variable. Since it takes only 2 bytes or 16 bits to store data, the range of short is also shorter than int. It ranges from -32,768 to 32767 (inclusive) or -2^15 to 2^15 -1. You might be wondering why upper bound is 255 and lower bound is -256 but that's because we have included zero in between.

Java - String charAt Example - How to get first and last characters

The charAt(int index) method of java.lang.String class can be used to retrieve a character from given index. The method returns a character, you can see its return type is char. The index starts from zero and ranges to length() - 1 where length() return the length of String. It's similar to an array where the first element is stored at zeroth index and the last element is stored at length -1 index because String is nothing but backed by a character array. If the value of the index is invalid i.e. it's lower than zero or negative or higher than length - 1 then this method throws an IndexOutOfBoundsException. In this article, I'll show you a couple of example of how to use the charAt() method to retrieve a character from String in Java.

2 Ways to Add Binary Numbers in Java - Coding

In the last article, I have shown you how to subtract binary numbers in Java and today, you will learn the opposite i.e. how to add binary numbers in Java. You can do binary addition in Java either by writing your own logic or by taking advantage of the Java API, which allows you to convert a binary String into a binary number. Though, if you want you can also use the logic I have shared in my earlier post about how to check binary numbers to verify input before converting it to a binary number. In this article, we'll take a look at both methods of adding two binary numbers in Java.

JDBC - How to get Row and Column Count From ResultSet in Java

One of the common problem in JDBC is that there is no way to get the total number of records returned by an SQL query. When you execute a Statement, PreparedStatement, or CallableStatement using execute()or executeQuery() they return ResultSet and it doesn't have any method to return the total number of records it is holding. The only way to find the total number of records is keeping the count while you are iterating over ResultSet while fetching the result. This way, you can print the total number of rows returned the SQL query but only after you have processed all records and not before, which may not be the right way and incur significant performance cost if the query returns a large number of rows.

How to change date format of String in Java 8

One of the common programming task in Java is to change the date format of a given Date or String. For example, you have something like "2017-01-18 20:10:00" and you want to convert it that date into "2017-01-18", or you want to convert from dd-MM-YY to MM-dd-YY or to any other format of your choice and need, but a valid date format as per Java specification. How will you do that? Well, it's not that difficult. It's just a two-step process. In the first step, you need to parse String to create an equivalent date using current format and then once you got the date, you need to again convert it back to String using the new format. The same process is repeated in both Java 8 and before, only corresponding API and classes changes.

Java - Convert String to Boolean Example

There are two ways to convert a String to boolean in Java, first, by using Boolean.parseBoolean() method and second, by using Boolean.valueOf() method.The parseBoolean() method returns an equivalent boolean value of given String, for example, if you pass "true" it will return the primitive boolean value true. Similarly, if you pass "false" it will return false. The good thing about this method is that it is case insensitive, which means if you pass "true", "TRUE", or "True" you will still get a true boolean value.

How to Subtract two Binary Numbers in Java - Solution

Binary subtraction is very similar to binary addition which we have learned in the last article. In this tutorial, you will learn how to subtract two binary numbers. Similar to the last article, we'll see two ways, first by converting binary String to a binary number and then doing subtraction. You can use the Java API Integer.toString(number, radix) for that. On second solution you will learn to develop the logic to perform binary subtraction in Java program by using rules you might have learned in your computer classes. Here is a little summary of how binary subtraction works.

Java String 101 - Everything You Want to Know about String in Java

someone might question that why do we need another article about string in Java, haven't we had enough about the string is already written? Yes, I agree there are a lot of articles related to Java string covering topics like how to use Java String, an example of Java string and almost everything you can do with string in Java. But, I wanted to document my experience of using String in Java and some nasty and little-known things I discovered about the Java String class, which may not be obvious to many Java developers. A string is available in almost every programming language and its probably the most used data structure or a data type, hence a good knowledge of String is very important for every Java developers.

Difference between OCAJP and OCPJP Certification Exams for Java Programmers

Earlier when Sun Microsystems was in charge of Java, the popular Java certifications were called "Sun Certified Java Programmer" or "SCJP" and that time there was just one exam, you need to pass to become a certified Java Developer, but when Oracle took over Sun Microsystems on 2010, the SCJP goes away and OCAJP and OCPJP born. Since Oracle already has his certifications for database administrations e.g. OCA which stands for Oracle certified associates and OCP, which stands for Oracle Certified Professional, it introduces new Java certifications to match their existing hierarchy and they are known as OCAJP and OCPJP in the Java world.

3 ways to convert String to byte array in Java - Example Tutorial

Today, I am going to discuss one of the common tasks for programmers, converting a String to a byte array. You need to do that for multiple reasons e.g. for saving content to a file, sending over a network or maybe some other reason. Suppose you have a String "abcd" and you want to convert it into a byte array, how will you do that in a Java program? Remember, String is made of the char array, so it involves character to byte conversion, which is subject to character encoding intricacies. Thankfully, Java provides a convenient getBytes() method to convert String to byte array in Java, but unfortunately, many developers don't use it correctly. Almost 70% of the code I have reviewed uses getBytes() without character encoding, leaving it on the chance that platform's default character encoding will be same as of the source String.

Eclipse - Unsupported major.minor version 53.0, 52.00, 51.0 Error in Java

The UnsupportedClassVersionError is a big nightmare for Java developers, probably the next biggest after NoClassDefFoundError and ClassNotFoundException but its slightly easier to solve. The root cause of this error is that your code is compiled using higher JDK version and you are trying to run it on the lower version. For example, the Unsupported major.minor version 53.0 means your code is compiled in JDK 9 (the class version 52 corresponds to JDK 9) and you are trying to run it on any JRE lower than Java 9, probably JDK 8, 7, or 6.

What is difference between an int and Integer in Java?

The first and foremost difference between an int and Integer or a char and Character is that former is a primitive data type while later is a class, also known as wrapper class because they wrap primitive data type inside it. When you first start learning Java, you start with primitive data types e.g. int, long, char, byte, boolean, float, and double but slowly you learn about Object and sometime later you know about Integer, Long, Character, Byte, Boolean, Float, and Double. At this point in time, you may wonder, what is the real difference between an int and Integer? isn't both same? We can pass Integer where int is expected and vice-versa then why on the earth we have both int and Integer?

5 Best books to learn JDBC - Java Programming

The JDBC (Java Database connectivity) is one of the important API in Java programming language which allows a Java program to connect to any database e.g. Oracle, Microsoft SQL Server, MySQL, PostgreSQL or any other. It's very importnat API to learn and master for both core Java and Java EE professional given ubiquitous nature of Database in real world application. Despite its importance, many Java developer lack essential JDBC skills e.g. they are not familiar with Connection, Statement, connection pool, calling stored procedures and executing transaction in JDBC. One reason for that is very limited or coverage of JDBC essentials in front line Java books e.g. Head First Java 2nd Edition.

How to lock a File before writing in Java? Example

A file is one of the oldest ways to store data and share data but if you are working in a shared file i.e a file which can be read or write by multiple readers and writers, you need to make sure that the file is locked before you try to write on it. This is needed to ensure that someone doesn't overwrite the data you are writing. Fortunately, Java provides a mechanism to lock a file before writing using the FileLock interface. You can get the handle of FileLock by using FileChannel for writing to a file. The FileChannel class is generally used to write faster in the large file and one of the common way to write binary data in Java.

How to Create Random Alphabetic or AlphaNumeric String of given length in Java - Example

Suppose, you want to generate an alphabetic or alpha-numeric string of given length in Java? How do you do it? Well, if you are like me, you probably search a library e.g. Apache commons-lang for something which can do this task. It's a good thing. There is no point on re-inventing a wheel if a tried and tested solution already exists. In fact, Effective Java, the most respected book in Java world also suggest to know and use your library. In fact, Apache commons-lang does have a class called RandomStringUtils, which allows you to generate Random alphanumeric String in just one method call as shown below:

RandomStringUtils.randomAlphanumeric(20).toUpperCase();

This works great for many practical purposes but if you are generating security sensitive identifier then this is not 100% secure.

Top 5 Free Core Spring, Spring MVC, and Spring Boot Courses for Beginners to learn Online

I have been sharing a lot of resources e.g. books and courses recently and when I published my list of Top 5 courses to learn Spring and Hibernate, many of my readers asked about a similar list of free courses to learn Spring Framework e.g. Core Spring, Spring MVC, Spring Security, and Spring Boot. That request was always back of my mind but I couldn't get time to put together a list, which I can share with you guys, but today is the day. In this list, I have compiled some of the best online free courses to learn Spring Framework from scratch, online at your own pace. You can not only learn core Spring e.g. a framework which provides dependency injection, but also Spring MVC, the most important framework for a Java Web Developer, Spring Security, and Spring Boot to take your career to next level.

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

The java.util.Collections class provides shuffle() method which can be used to randomize object 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 element 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. Since this method except for fora List, you can also pass it to LinkedList, VectorCopyOnWriteArrayList, and others, which doesn't implement the RandomAccess method.

Java Enum Tutorial - 10 Things Java Devs Should Know about Using Enum

Apart from the Class and Interface, Enumeration type or Enum is another popular type in Java programming language. Enum allows you to represent a fixed number of well-known things in a type-safe manner e.g. days of the week, days of the month, planets in solar system, buttons on remote control, keys on keyboard and suits on playing cards. Before Enum was introduced, prior to Java 1.5, integer and string constants are used to represent the fixed number of things, known as enum int pattern and enum string pattern as described in classic Effective Java by none other than Joshua Bloch. Though they served the purpose, they had some major drawbacks which resulted in poor quality code.

Top 5 Free JavaScript Books for Beginners - Download PDF or Read Online

The internet is full of good things and one of them is free eBooks and PDF. Programmers can almost run anything by these free books. Earlier I have shared some of the free JavaScript tutorials and in this article, I am going to share 5 good books to learn JavaScript which are free to read online or allow you to download PDF for offline reading. JavaScript is probably another language I recommend someone who knows Java, Why? because it's really ubiquitous. There is almost no website which is not using JavaScript in one or other format. Some use JavaScript for client-side scripting and animation, while other use JavaScript on the server side with libraries like node.js, it forms the unique triangle with HTML and CSS.

Top 75 Programming Interview Questions Answers to Crack Any Coding Job Interview

Hello guys, if you are preparing for your next Programming Job interview and looking for some frequently asked Coding or Programming questions to practice then you have come to the right place. In this article, I am going to share some of the most commonly asked Coding questions from Programming Job interviews. In order to do well on the Coding interview you need practice, you just can't go there and expect to solve the coding problems in limited time. Sometimes, the interviewer also asks little bit easier coding questions on telephonic interview e.g. revering array in place or reversing a string in place.

How to java.lang.NoClassDefFoundError: org/springframework/beans/factory/SmartInitializingSingleton in Spring Boot

Problem:
I was trying to run a HelloWorld program using Spring Boot when I got this error:

Exception in thread "main" java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration#propertySourcesPlaceholderConfigurer due to internal class not found. This can happen if you are @ComponentScanning a springframework package (e.g. if you put a @ComponentScan in the default package by mistake)
at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:52)
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:92)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForBeanMethod(ConfigurationClassBeanDefinitionReader.java:174)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForConfigurationClass(ConfigurationClassBeanDefinitionReader.java:136)

A Simple Example to Check if File is Empty in Java

One of the readers of my blog Javarevisited emailed me yesterday about how to check if a file is empty in Java and that's why I am writing this post to show that using an example. The common approach for checking if a file is empty or not is to first check if the file exists or not and then check if it contains any content, but Java has done that hard work for you. Well, it's pretty easy to check emptiness for a file in Java by using length() method of the java.io.File class. This method returns zero if the file is empty, but the good thing is it also returns zero if the file doesn't exist. Which means you don't need to check if the file exists or not.

Difference between a List and ArrayList Reference Variable in Java?

Someone who is just starting with Java programming language often has doubt about how we are storing an ArrayList object in List variable, what is the difference between List and ArrayList? or why not just store the ArrayList object in ArrayList variable just like we do for String, int, and other data types. Well, the main difference between List and ArrayList is that List is an interface while ArrayList is a class. Most importantly, it implements the List interface, which also means that ArrayList is a subtype of List interface. In Java or any object oriented language, super type of variable can store an object of subtype. This is known as Polymorphism because any virtual method will be executed from subclass only, even though they were called from super type. This is the beginning, now let's see those two questions as well.

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

There are multiple ways to compare two dates in Java, it also depends on upon 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 equals() method of java.util.Date class. This method will return true if both dates are equal, precisely both thave 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 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 before() and after() method of Date class, they are more readable and easy to use.

Java - InstanceOf KeyWord Example and Tutorial

The Java programming language and JVM are full of hidden gems and even though I am using Java for more than a decade I still get surprised of features which I didn't know for quite some time e.g. shutdown hook, covariant method overriding, and JVM option to refresh DNS cache.  The instanceof operator is also one of the rarely known features of Java, It is used to check if an object is the instance of a particular Class or not. It returns true if the object is an instance of the class, otherwise, returns false. You might have seen usages of instanceof operator in Java while overriding equals() method. Since for checking equality of two instances, the first step is to verify whether they are the instance of the same object or not, you can use the instanceof operator there.

Top 50 Basic Core Java Interview Questions with Answers

If you are preparing for your next Core Java interview and looking for some common question to practice or check your knowledge then you have come to the right place. In this article, I'll share 50 Core Java Interview Questions from various companies. I have already discussed the answers to these questions in this blog or Javarevisited, so I have just put the link. First, you should try to answer it yourself and if you cannot then go to the link and find the answer. You can also compare your answer with mine and learn a few things here and there. In most of my interview post, I have also shared some common techniques to drive interview towards your comfort zone and how to leave a long-lasting impression on the interviewer, you can use those techniques to do well on your Java interviews.

Is it possible to instantiate an Abstract class in Java?

Earlier I have shared one of the frequently asked questions in Java, can we make an abstract class final in Java and my readers really liked and asked for more such questions. So, today I am going to talk about whether we can create an instance of an Abstract class in Java or not? This is another interesting core Java question you will find on telephonic interviews or Oracle certified Java programmer certification. The answer to this question is simple, No, you cannot instantiate an abstract class in Java because it is abstract, it is not complete hence it cannot be used.  When you create an instance of a class, its's constructor is called and even though abstract class can have a constructor, the compiler will not allow you to create an instance of the class. It's a compile-time error to create an instance of an abstract class in Java.

How to use Queue in Java - Example Tutorial

The JDK provides implementation of several data structure in Java collection framework e.g. ArrayList is a dynamic array, LinkedList represents a linked list, HashMap represents hash table data structure, and Queue interface represent queue data structure. Btw, If you are not familiar with data structure itself then see Introduction to Data Structures & Algorithms in Java, a good course to start with the essential data structure in Java. The Queue data structure allows you to process elements in the first in first out order and that's why it is also known as FIFO data structure. In order to provide first in first out functionality, it allows you to insert data at one end and delete data from other ends, also known as consuming data. If you need to process objects in the FIFO order you can use a Queue to store them.

Top 4 Free Microsoft SQL Server Books - PDF Download or Online Read

Hello Guys, today, I am going to share some of the good database and SQL server books which are freely available on the internet for reading online or download as PDF. If you have been reading this blog then you know that I love books, I love to read books and I love to collect books that's why I have a big online and offline library. Many people question me do I really find to read all books which I share? Well, I don't read all books page by page, unless and until its something like Effective Java or Clean Code. I mostly skim through books and stopping on interesting and new things, which I don't know or probably have a misconception, but I do like to refer books many times. If I skim through a book, I know where can I find more information about a particular concept and then I explore it in more depth.