How to use Map.compute(), computeIfPresent() and ComputeIfAbsent in Java? HashMap and ConcurrentHashMap 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 becomes 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.

How to use LinkedList in Java? Singly LinkedList and Doubly LinkedList Example Tutorial

Hello friends, we meet again on our journey to Java. I hope you guys are enjoying Java and are trying hands-on too. Today we are gonna discuss a very easy topic (yeah, I mean it :p). But, do not get carried away just by "easy", this is the hottest topic asked in various interviews, exams, and development purposes too. So, what's the wait? Let's start!  As usual, let's start with a scenario. Let's say you want a data structure that stores data in a sequential manner, like an array. But, you don't know the size yet while initializing the data structure. Arrays don't support that, they need a size beforehand. So, what should we do? Do not worry, as Java is here to help us again. Let's explore it then!

How to get First and Last Element of LinkedList in Java [Example]

Hello guys, if you are wondering how to get the first and last element from Java LinkedList then you have come to the right place. Earlier, I have shared the best Data structure and algorithms courses and in today's post, I will teach you how to get the first and last element of a linked list in Java. This is one of the common coding problems but we will see it from different angles. In Java, you don't need to write and create your own LinkedList, there is a built-in class called java.util.LinkedIn and you can use that class whenever you need a linked list data structure. 

Difference between Thread.yield and Thread.sleep in Java? Answer

Sleep vs yield in Java

Sleep and yield are two methods that are used to get CPU back from Thread to Thread Scheduler in java but they are completely different than each other. The major difference between Sleep vs yield is that sleep is more reliable than yield and it's advised to use sleep(1) instead of yield to relinquish CPU in multi-threaded Java applications to give an opportunity to other threads to execute. In this Java tutorial, we will what are the differences between yield and sleep in Java. But before seeing the difference between sleep and Yield let's see some similarities between yield and sleep in Java

[Solved] java.lang.ClassNotFoundException: org.Springframework.Web.Context.ContextLoaderListener in Java and Spring

Problem : You are getting java.lang.ClassNotFoundException : org.Springframework.Web.
Context.ContextLoaderListener in your Spring-based Java Web application.
Cause: This error comes when you are using the Spring MVC framework in your Java Web application and configured org.springframework.web.context.ContextLoaderListener as a listener in your deployment descriptor also known as web.xml, but the JAR which contains this class is not available in the web application's CLASSPATH.

How to fix org.springframework.beans.factory.BeanCreationException: Error creating bean with name X [Java Spring]

If you are using the Spring framework in your Java application and getting this error during startup it means Spring is not able to initialize the bean X and add it into its application context, Why? There could be multiple reasons like a typo on the spring bean name. Let's take a closer look at the stack trace to find out the real reason:

BeanInstantiationException: Could not instantiate bean class [X]: No default constructor found; nested exception is java.lang.NoSuchMethodException: X.()

Here X is the class, which is declared as Spring bean. The error clearly says that the default constructor is not present in class X.

Difference between Serializable vs Externalizable in Java - Interview Question

What is the difference between Serializable and Externalizable in Java is famous core Java interview questions and for some of them its one of those difficult Java question, which no one wants to see in Java interview. I was in that category until I read Effective Java and explored How Serialization works in Java and find out more about the Serialization process. What makes Serialization questions tricky is, Serialization as a persistence mechanism is not very popular. Many programmers prefer databases, memory-mapped files, or simple text files over Serialization. But Serialization has a distinguished advantage over these mechanisms.

What is the use of DispatcherServlet in Spring MVC? Interview Question Example

Hello guys, In today's article we are going to discuss one interesting and the important Spring MVC concept, which is also a popular Spring Interview question. How DispatcherServlet works internally in Spring MVC or What is the role of DispatcherServlet in Spring MVC are some of the frequently asked Spring MVC Interview Questions. You might have seen them already during your previous Java web development interviews but if you have not, it's a good question to know. In this article, I'll answer these questions by explaining What is DispatcherServlet and its importance in Spring MVC. The DispatcherServlet is one of the important components of the Spring MVC web framework and acts as a Front Controller.

What is @Bean Annotation in Spring Framework? Example Tutorial

Hello Java programmers, if you are wondering what is @Bean annotation in Spring Framework, what is the purpose, and how to use it then you have come to the right place. Earlier, I have shared the best free Spring core and spring MVC courses and In this tutorial, you will learn the most frequently used Spring annotations @Bean, which are used to define different types of beans. Beans are the fundamentals of Spring framework, they represent the POJO class which is created and managed by Spring Framework. Whole Spring framework is about beans and their relationships. 

How to delete multiple elements from a LinkedList in Java? SubList() Example

Hello guys, if you are looking for an easy way to remove a sub set of elements from a LinkedList in Java then you have come to the right place. In the past, I have shown you how to sort a LinkedList in Java and how to create your own linked list implementation in Java and in this article, I am going to introduce you with an interesting method which can be used to delete a portion of LinkedList in Java in shot. Yes, there is a method exists  but not many Java developer knows about it. The method is called subList() and you can use this method with clear method in Java to delete a portion of linked list in one shot.

What is TreeMap in Java? HashMap vs TreeMap Example Tutorial

Hello guys, I hope you all are doing well and having lots of fun reading and learning Java Collections together. Today we are here a meet again on our journey of Java. I hope you all have seatbelts buckled up as today it's gonna be an adventurous ride while learning something that is most used in many production applications, coding, and whatnot. Today's topic, TreeMap in Java is very important because it holds a very significant feature Java development kit provides. This is also one class which many Java developer doesn't pay attention but it is really used for many use cases. Most Java developer just keep their attention to ArrayList, HashSet, and HashMap and thus missing out on many cool Java collection classes like TreeMap, WeakHashMap, and LinkedHashMap which saw earlier.

How ThreadLocal variables works in Java? Explained

Hello guys, ThreadLocal variable is an interesting concept and class from Java API. Not many developer knows about it and very few know how to use it correctly. A couple of years ago it was also a popular Java interview questions for experienced developer but over the years, it lost the popularity as more and more people are now asking about Phaser, CompletableFuture, ForkJoinPool, and other newly added concurrency utilities. ThreadLocal variables, as name suggests is local to thread, which means every thread has there own copy. This means they don't need to look at the main memory when they want to use that variable and best thing is that the variable is not even shared between threads so no locking or synchronization is needed. 

Difference between JIT and JVM in Java? Answered

The main difference between JIT and JVM is that JIT is part of JVM itself and its main function is to improve the performance of JVM by directly compiling some hot code (code that executes above a certain threshold) into native instruction. JIT stands for Just In time compilation and JVM stands for Java Virtual Machine. JVM is a virtual machine used in Java programming platforms to execute or run Java programs. The main advantage of JVM is that JVM  makes Java platform-independent by executing bytecodes. Java source code is compiled into class files, which contain bytecode.

Visitor Design Patterns In Java Examples Tutorial

Hello guys, if you want to learn Visitor design pattern in Java then you have come to the right place. Earlier, I have covered many design patterns like Decorator, Strategy, State, Composite, Adapter, Command, Template, Factory, Observer and even few Microservice patterns like SAGA and Database per service and in this article, I will talk about Visitor Design Pattern and how to implement in Java. You will learn things like what is Visitor design pattern, what problem it solves, what are pros and cons of Visitor design pattern, when to use Visitor pattern as well as any alternatives of Visitor Pattern in Java. I will also show you a real world example of Visitor design pattern, but, before we get to the 5 best examples that will teach you all about design patterns in Java, let me tell you a little bit more about what it really is.

Difference between 32-bit vs 64-bit JVM in Java?

Hello Java Programmers, if you want to learn Java virtual Machine in-depth and wondering what is the difference between a 32-bit and 64-bit JVM and which one should you use and why? then you have come to the right place. Earlier, I have shared the best JVM books and online JVM courses and in this article, I am going to talk about 32-bit vs 64-bit JVM and their pros and cons. This is also a common Java interview question for beginners and intermediate Java programmers. I have tried to answer this question to the point that's why this article is a short but informative one. You will find out what they are, how they are different, how much heap size, and the pros and cons of each of them. 

10 Examples Of Mockito + JUnit in Java for Unit Testing

Hello guys, if you are writing unit test in Java then you know how difficult it is to write especially if you are testing a class which is dependent upon other class like HttpClient and you cannot connect to actual server. At those time, a mocking library like Mockito comes to rescue. Given the increased focus on unit testing and code coverage, I have find myself using Mockito more and more along with JUnit in last a couple of years but I haven't written many articles on Mockito yet but that is chaging now. In this article, I am going to share 10 essential Mockito examples which I belive every Java programmer should know. But, before we get to the 10 best examples that will teach you everything there is to know about Mockito in Java, let me tell you a little bit more about what it really is.

How to convert Java 8 Stream to Array and ArrayList in Java? Example Tutorial

It's relatively easy to convert a Stream to an array in Java 8 by using the toArray() method of java.util.Stream class. By using this method you can convert any type of Stream to a corresponding array like a Stream of Strings can be converted into an array of String, or a Stream of integers can be converted into an array of Integers. The Stream.toArray() method is also overloaded, the one which doesn't take any parameter returns an Object[] which might not be very useful, particularly if you want to convert Stream of T to an array of T.

Array length vs ArrayList Size in Java [Example]

One of the confusing parts in learning Java for a beginner to understand how to find the length of array and ArrayList in Java? The main reason for the confusion is an inconsistent way of calculating the length between two. Calling size() method on arrays and length, or even length() on ArrayList is a common programming error made by beginners. The main reason for the confusion is the special handling of an array in Java.  Java native arrays have built-in length attribute but no size() method while the Java library containers, known as Collection classes like ArrayList<>, Vector<>, etc,  all have a size() method. 

How to create an ArrayList from Array in Java? Arrays.asList() Example Tutorial

One of the common problems faced by junior and less experienced Java developers is converting an array to ArrayList e.g. they are getting an array from somewhere in their code and then want to create an ArrayList out of that so that they can add more elements and use other library methods which operate with ArrayList or List. The simplest way to convert an array to ArrayList is by using the Arrays.asList() method, which acts as a bridge between Collection classes and array data structure. This method returns a List that contains elements from an array. 

Is it Possible to add static or private methods in Java interface?

Can you add a static or private method in an interface in Java? or is it possible to add a private or static method in Java interface? or can you add a non-abstract method on an interface in Java? are a couple of popular Java interview questions which often pop up during telephonic interviews. Well, prior to Java 8, it wasn't possible to add non-abstract methods in Java but nowadays you can add non-abstract static, default, and private methods in the Java interface. The static and default methods were supported as part of interface evolution in Java 8 and you can add private methods on an interface from Java 9 onwards.