What is Log4j 2 RCE issue CVE-2021-44228? How to solve Log injection? [Tactical and Permanent Fix]

Hello guys, since the last couple of days, there is a lot of chaos going into the Java world due to the Log4j2 issue which allows Remote code execution (RCE), the CVE-2021-44228, which is designated a zero-day vulnerability. Everyone is busy whether their Java application is impacted and given the popularity of Log4j it's a good chance that your application will be impacted.  Even if you are not using Log4j2 directly, they might be used by the framework or library you use like Spring Boot, Hadoop, Elastic Serach, or Struts. This is kind of a serious issue becuase RCE Vulnarabilyt means it allows hackers to execute code in your servers, and this has been used in past on many breaches like the 2017 Equifax data breach but its not time to lose calm and understand the impact and whether your app is affected or not and what you can do in short term to prevent it. 

Top 5 Course to Crack Google's Associate Cloud Engineer Certification Exam in 2025 - Best of Lot

Hello guys, If you are looking to pursue a career as a Google Cloud Engineer or merely just want to acquire a cloud certificate to add to your colorful resume, then taking the Google Cloud Engineer exam might be just the right thing for you. Google Cloud Platform or GCP is one of the top 3 public cloud providers along with AWS and Microsoft Azure and the demand for certified Google cloud professionals is growing exponentaitonal because of increased adoption of the Google Cloud Platform. If you already have a fair amount of experience, then you may want to go for the Professional Cloud exam. But if you are a newbie, or looking to add more certifications to add your CV then the Associate Cloud Engineer exam is the way to go.

Pluralsight Free Weekend - 7500+ Pluralsight Courses FREE for 3 Days

Hello folks,  I have exciting news to share with you that Pluralsight is running their Free weekend from 19th to 21st November, which means all of their 7500+ courses are free this weekend. This is an excellent opportunity to try and see the high-quality courses from Pluralsight. If you don't know, Pluralsight is one of the most popular online learning platforms for programmers and developers. Whether you want to learn Java, Python, JavaScript, Web Development, or Data Science, Pluralsight has courses for them. The best thing about Pluralsight is that its creators are reputed and authoritative. For example, there are many Java champions like Richard Warburton and Jose Paumard who have created excellent Java courses. 

10 Tips to create Maintainable Java Applications

Hello all, if you are in software development then you know that creating an application is easy but creating a maintainable application that can pass the test of time in production is rather difficult and that's the main reason experienced Sofware developers are paid higher salaries compared to many other jobs. In this article, I am going to share with you some tips on creating maintainable Java applications which will help you not just in the new year, but also in all the coming years in your software development career.  One aspect of development, which is often overlooked by developers is to create applications that are both easy to maintain and support. Since software spends 90% of its lifetime in maintenance mode, it's very important that your application is easy to configure, support, and maintain. 

How to HashMap in Java? Example Tutorial

Hello friends, we are here today again on our journey to Java. I hope everyone is fine and ready to board our train of knowledge. Today we are gonna learn something very interesting and very exciting, yes I am talking about the HashMap class in Java which is the implementation of hash table data structure. In the past, I have shared my thoughts on How HashMap works in Java as well as frequently asked HashMap interview questions but I have never shared an example of how to use HashMap in Java, or when to use HashMap. Today's topic will definitely be very useful in coding and programming. This topic would surely decrease your time complexity if any task very significantly :p 

So what's the wait? Let's start!

How to Check/Uncheck CheckBoxes in a Page using jQuery? Example Tutorial

In the last couple of articles, I have shared a couple of useful jQuery tips like reloading web pages and working with tag selectors. Today, I'll show you how to check or uncheck a particular checkbox using jQuery, one of the most popular JavaScript frameworks. jQuery provides CSS like selectors which can make this kind of task trivial. If you remember, in HTML a checkbox is checked if the "checked" attribute is present and its value is not false, otherwise, it's unchecked. By using jQuery function prop() you can dynamically add this attribute or if present we can change its value i.e. checked=true to make the checkbox checked and checked=false to mark the checkbox unchecked.

Difference between Stable and Unstable Sorting Algorithm - MergeSort vs QuickSort

Recently in one interview, after some initial questions about sorting algorithms e.g. how do you write QuickSort or the difference between QuickSort and MergeSort, the interviewer asked about do you understand the difference between stable and unstable sorting algorithms? This question was new to my reader, so he says, Sorry, never heard about that. The story ended there, and Interviewer moved on to the next question but like many of us, my reader went on to find more unanswered questions and ultimately he asks me what is the meaning of a stable and unstable sorting algorithm? Some of you might be heard about it and many of you might not know about this distinction, I'll try to answer this question in this article.

How to solve java.lang.classnotfoundexception sun.jdbc.odbc.jdbcodbcdriver in Java 8

java.lang.classnotfoundexception sun.jdbc.odbc.jdbcodbcdriver exception comes in Java 8 because it has removed the JDBC ODBC bridge driver class "sun.jdbc.odbc.jdbcodbcdriver" from JDK and JRE. This class is required to connect any database using Object database connectivity driver e.g. Microsoft Access, but unfortunately, you cannot use it from JDK 8 onward. In order to solve this error, just use the Jackcess library or a commercial driver like HXTT. Normally, in pre-Java 8 world, java.lang.classnotfoundexception sun.jdbc.odbc.jdbcodbcdriver error comes when you try to connect to the Microsoft Access database from Java using JDBC and JDBC ODBC bridge driver is not available in the classpath.

Does Standard Column Width of 80 On Coding Make Sense in Modern Era of Big Monitors?

One of the oldest coding practices is to keep line width 80, and many of us follow it blindly but have you ever thought about why we have this practice in the first place? I believe it was to make your code more readable in the age of small monitors so that the whole content can fit on the screen, or it might have originated from the age of punch cards, which was used to be 80 columns wide. This sounds reasonable when we think about those old days but do you think this rule makes sense now? We are now living in the age where most of the developers have got large monitors, which can show up to 180 characters, doesn't this is wastage of precious monitor space? It also makes your code unnecessary long, than it actually is.

How to Split String in SQL Server and Sybase? Example Tutorial

Sometimes we need to split a long comma-separated String in a Stored procedure e.g. Sybase or SQL Server stored procedures. It's quite common to pass comma delimited or delimiter separated String as an input parameter to Stored procedure and then later split comma separated String into multiple values inside stored proc. This is not just the case of the input parameter but you can also have a comma-separated string in any table data. Unfortunately, there is no split() function in Sybase or SQL Server 2005 or 2008 which can directly split a string based on delimiter just like in the Java string split method. 

How to Count Number of Leaf Nodes in a Binary Tree in Java ? [ Iterative and Recursive Solution]

Hello guys, today I am going to talk about an interesting binary tree-based coding problem from Programming Job interviews. If you have attended a couple of technical interviews then there is a good chance that you already have seen this question about counting the number of leaf nodes in a binary tree. If you know how to solve this problem then it's well and good but if you haven't don't worry, you will learn in this article. If you follow this blog then you might know that I have discussed a lot of data structure and algorithms problems here, including array, linked list, hash table, binary tree, and binary search tree. 

How to Load Resources from Classpath in Java with Example

Classpath in Java is not only used to load .class files, but also can be used to load resources e.g. properties files, images, icons, thumbnails, or any binary content. Java provides API to read these resources as InputStream or URL. Suppose, you have a properties file inside the config folder of your project, and you want to load that properties file, how do you do that? Similarly, you have icons and thumbnails for your web applications on the icons directory of your project, how do you load them? The answer is by using java.lang.Class' getResource() and getResourceAsStream() method. These methods accept the path of resource as String and return URL and InputStream respectively.

6 ways to declare and initialize a two-dimensional (2D) String and Integer Array in Java - Example Tutorial

Declaring a two-dimensional array is very interesting in Java as the Java programming language provides many ways to declare a 2D array and each one of them has some special things to learn about. For example, It's possible to create a two-dimensional array in Java without specifying the second dimension, sounds crazy right? but it's possible because a two-dimensional array in Java is nothing but an array of array. You can even create a two-dimensional array where each subarray has a different length or different type, also known as a heterogeneous array in Java. This means it's possible to create a two-dimensional array with variable column length in Java.

How to Calculate Difference between two Dates in Java (In Days) - Example Tutorial

If you are not running on Java 8, then there are two ways to calculate the difference between two dates in Java in days, either by using standard JDK classes e.g. java.util.Date and java.util.Calendar or by using the joda-time library. Unfortunately, Java's old Date and Calendar API is buggy and not intuitive, so many of us by default use Joda for all date and time arithmetic. In this example, you will learn how to find the number of days between today and any date entered by a user using Joda, as well as without using any third-party library. When I first time face this problem, I thought what's a big deal about finding the difference between dates? If you can convert Date to milliseconds then finding a number of days, months or years are just a matter of simple arithmetic, but I was WRONG. I was not thinking about the real-world date and time nuisance like leap seconds, leap years, and daylight saving time.

How to implement Bucket Sort in Java? [Solved] - Example Tutorial

In recent years, one of the questions I have increasingly seen in programming job interviews is about constant time sorting algorithms like do you know any O(n) sorting algorithm? how do they work? When I first encountered this question, I had no idea whether we can sort in constant time because even some of the fastest sorting algorithms like QuickSort or MergeSort take O(N log N) time for sorting on their average case. After some research, mainly by going through the classic CLRS book and this DS and Algorithms course by Tim Buchalka and Goran Lochert on Udemy, I come to know that there indeed are some constant time or linear time sorting algorithms like bucket sort, counting sort, and radix sort, which can sort an array in O(n) time but they work with only a special set of input.

2 Best Open source Java Libraries to Create PDF documents - iText vs Apache FOP

PDF format is a popular format for sending receipts, email confirmation, and other documentation and we often have a requirement to create PDF documents using Java, mostly in JSP pages. Since most of the official documentation uses PDF format nowadays, it becomes imperative to support PDF files. Recently I received a couple of questions regarding the suggestion of open-source Java PDF libraries, like which is the best open source PDF library in Java or should I use iText or Apache FOP in my Java application for PDF processing. These questions motivates me to write this post. In this article, I will share a couple of Java based open source PDF libraries, both FREE and with some licensing fees, which you can use to generate PDF documents in Java projects.

What is difference between ArrayList and ArrayList<?> in Java?- Raw Type vs Wildcard Example Tutorial

One of my readers asked me about the difference between ArrayList vs ArrayList< in Java?>, which was actually asked to him in a recent Java development interview. The key difference between them is that ArrayList is not using Generics while ArrayList is a generic ArrayList but they look very similar. If a method accepts ArrayList or ArrayList<?> as a parameter then it can accept any type of ArrayList like ArrayList of String, Integer, Date, or Object, but if you look closely you will find that one is raw type while the other is using an unbounded wildcard. What difference that could make? Well, that makes a significant difference because ArrayList with raw type is not type-safe but ArrayList<?> with the unbounded wildcard is type-safe.

Difference between Abstraction and Encapsulation in Java? OOP Question Answer

Both Abstraction and Encapsulation are two of the four basic OOP concepts which allow you to model real-world things into objects so that you can implement them in your program and code. Many beginners get confused between Abstraction and Encapsulation because they both look very similar. If you ask someone what is Abstraction, he will tell that it's an OOP concept which focuses on relevant information by hiding unnecessary detail, and when you ask about Encapsulation, many will tell that it's another OOP concept which hides data from the outside world. The definitions are not wrong as both Abstraction and Encapsulation do hide something, but the key difference is on intent.

Recursive Binary Search Algorithm in Java - Example Tutorial

The binary search algorithm is one of the most famous search algorithms in computer science. It allows you to search a value in logarithmic time i.e. O(logN), which makes it ideal to search a number on a huge list. For example, in order to search a number in a list of 1 million numbers will take around 210 comparisons compared to 1 million comparisons required by the linear search algorithm. The only thing is that the list must be sorted before you can use a binary search algorithm and it must support index-based search. That's why binary search is often implemented using an array because doing a binary search with a linked list will not be fast because it doesn't provide index-based access i.e. O(1) access. You have to traverse to that element to read its value in the linked list which is O(n), effectively reducing the performance of binary search to a sequential search algorithm.

3 Ways to Prevent Method Overriding in Java - Private, Static and Final Method Example Tutorial

Every Java programmer knows that final modifier can be used to prevent method overriding in Java because there is no way someone can override final methods; but, apart from final modifier, is there any other way to prevent method overriding in Java? This was the exact question, asked to one of my friend in a recent Java interview at one of the leading Investment bank. I guess, he was lucky to get this question because he already knows those tricks and was able to answer it quickly. When he told me about his experience,  I didn't understand why someone ask this question? What is the purpose? What they were trying to find out? I can understand if they have asked what's the best way to prevent method overriding in Java, or what is the risk of overriding? 

Java 8 Date Time - 20 Examples of LocalDate, LocalTime, LocalDateTime

Along with lambda expressions, streams, and several minor goodies, Java 8 has also introduced brand new Date and Time API, and in this tutorial, we will learn how to use Java 8 Date Time API with simple how-to-do task examples. Java's handling of Date, Calendar, and Time is long been criticized by the community, which is not helped by Java's decision of making java.util.Date mutable and SimpleDateFormat not thread-safe. It seems, Java has realized a need for better Date and time support, which is good for a community which already used to of Joda Date and Time API.

Difference between Stack and Queue Data Structure in Java? Example

Stack and Queue are two of the important data structures in the programming world and have a variety of usage. As opposed to the array and linked list, which are considered primary data structures, they are secondary data structures that can build using an array or linked list. You can use Stack to solve recursive problems and Queue can be used for ordered processing. The difference between Stack and Queue Data structure is also one of the common questions not only in Java interviews but also in C, C++, and other programming job interviews.

10 Examples of Converting a List to Map in Java 8

Hello guys, suppose you have a list of objects, List and you want to convert that to a Map, where a key is obtained from the object and value is the object itself, how do you do it by using Java 8 stream and lambda expression? Prior to Java 8, you can do this by iterating through the List and populating the map by keys and values. Since it's an iterative approach and if you are looking for a functional solution then you need to use the stream and lambda expression, along with some utility classes like Collectors, which provides several useful methods to convert Stream to List, Set, or Map.

How to Remove all Unused imports in a Java file - Eclipse Shortcut Example

How to remove all unused imports in Eclipse

Eclipse IDE gives a warning "The import XXX is never used" whenever it detects unused import in a Java source file and shows a yellow underline. Though unused import in Java file does not create any harm, it's unnecessary to increase the length and size of Java source file and if you have too many unused imports in your Java source file, those yellow underline and Eclipse warning affect readability and working. In my last post on Eclipse, we have seen some Java debugging tips on Eclipse and in this post, we will see Eclipse shortcut to remove all unused imports in Eclipse. 

How to get just DATE or TIME from GETDATE() in SQL Sever - Example Tutorial

The GETDATE is one of the most popular built-in methods of  Microsoft SQL Server, but unlike its name suggests, it doesn't return just date, instead, it returns date with time information e.g. 2015-07-31 15:42:54.470, quite similar to our own java.util.Date from Java world. If you want just a date like 2015-07-31, or just a time like 15:42:54.470 then you need to either CAST or CONVERT output of GETDATE function into DATE or TIME data type. From SQL Server 2008 onward, apart from DATETIME, which is used to store both date and time, You also have a DATE data type to store data without time e.g. 2015-07-31, and a TIME data type to store time without any date information like 15:42:54.470.

5 ways to Convert Java 8 Stream to List - Example, Tutorial

One of the common problems while working with Stream API in Java 8 is how to convert a Stream to List in Java because there is no toList() method present in the Stream class. When you are processing a List using Stream's map and filter method, you ideally want your result in some collection so that you can pass it to other parts of the program. Though java.util.stream.Stream class has toArray() method to convert Stream to Array, but there is no similar method to convert Stream to List or Set. Java has a design philosophy of providing conversion methods between new and old API classes e.g. when they introduced Path class in JDK 7, which is similar to java.io.File, they provided a toPath() method to File class.

How to distinguish logging per Client or Request in Java? Use MDC or Mapped Diagnostic Context in Log4j Example

The MDC or Mapped Diagnostic Context is a concept or feature of the Log4j logging library which can be used to group related log messages together. For example, by using MDC you can stamp a unique identification String like clientId or orderId on each log message, and then by using grep command in Linux, you can extract all log messages for a particular client or order to understand exactly what happened to a particular order. This is especially very useful in multi-threaded, concurrent Java applications where multiple threads are simultaneously processing multiple orders from multiple clients.  In such applications, searching for relevant log messages in a big log file where log messages for multiple orders or clients are overlapping is a big task.

How to find all Checked checkboxes in jQuery? Example Tutorial

Hello guys, suppose you have multiple checkboxes in your HTML page and you want to retrieve all checkboxes which are checked? How will you do that in jQuery? Well, you can use the pseudo selector like :checked to get all checked checkboxes. This selector checks for the checked property of the checkbox and returns only those checkboxes which have this property. For example, the following jQuery selector will return all the checkboxes which are checked:

$('input[type=checkbox]:checked')

In this, we are first selecting all input elements where type is a checkbox and then adding: checked to filter only those which are checked.

What is Default, Defender or Extension Method of Java 8 with Example

Java 8 now allows you to add non-abstract method implementations to interfaces by utilizing the default and static keywords. Methods with default keywords are known as default methods or defender methods in Java. Before Java 8, it was virtually impossible to change an interface once published. Any change like the addition of a new method would have broken all clients. That's why when Java 8 decided to switch to internal iterator implementation using the forEach() method, they face the daunting challenge of breaking all implementation of the Iterable interface. Since backward compatibility is a top priority for Java engineers, and it wasn't practical to break all clients, they came up with the idea of the default method.

How to convert float to long or int data type in Java? Example

Yesterday one of the new joiner Java Trainee Engineers from our team came to me and asked about how do you convert a float variable into a long or int data type? He was storing some values coming from another system in the database and only wanted to store values before the decimal point e.g. he was getting "3.144" and he wants to convert it to "3" to store into the database. The good thing was that API was returning a float primitive value and you don't need to convert a String to float etc. I asked him whether he needs routing or not, which he wasn't sure but it turns out that he didn't need that. I explained to him how to do that and that's what you will find in this article as well. In short, there are 3 ways to convert a float value into long or int in Java, but we will only focus on the long data type part.

How to Clone a Collection in Java? Deep copy of ArrayList and HashSet Example

Programmers often mistook copy constructors provided by various collection classes, as a means to clone Collection like List, Set, ArrayList, HashSet, or any other implementation. What is worth remembering is that the copy constructor of Collection in Java only provides a shallow copy and not a deep copy, which means objects stored in both original Lists and cloned List will be the same and point to the same memory location in the Java heap. One thing, which adds to this misconception is a shallow copy of Collections with Immutable Objects. Since Immutable objects can't be changed, It's Ok even if two collections are pointing to the same object. This is exactly the case of String contained in the pool, update on one will not affect the other.

How to use Stream with List and Collection in Java 8? filter + map Example Tutorial

Finally, Java 8 is here, after more than 2 years of JDK 7, we have a much expected Java 8 with lots of interesting features. Though Lambda expression is the most talked-about item of the coming Java 8 release, it wouldn't have been this much popular, if Collections were not improved and Stream API was not introduced. Java 8 is bringing on new Streams API java.util.stream package, which allows you to process elements of Java Collections in parallel. Java is inheritably sequential and there are no direct means to introduce parallel processing at the library level, stream API is going to fill that gap. By using Stream API in Java, you can filter elements of collection on a given criterion. For example,  if you have a list of orders, you can filter buy orders with sell orders, filter orders based upon their quantity and price, and so on.

How to fix java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver [Solution]

This error comes when you try to connect to the Microsoft SQL Server database from the Java program but the required JDBC driver is not available in Classpath or driver is available in CLASSPATH but the class loader is not able to find it due to classpath intricacies. Depending upon your situation, a solution could be as simple as downloading any of sqljdbc.jar, sqljdbc4.jar, or sqljdbc41.jar, based upon the Java version you are using and adding them into CLASSPATH as set CLASSPATH = %CLASSPATH%; (path to Microsoft JDBC driver) in Windows. BTW, in most of the cases "java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver" comes because of classpath intricacies.

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

The simplest way to convert an array to comma separated String is to create a StringBuilder, iterate through the array, and add each element of the array into StringBuilder after appending the comma. You just need Java 1.5 for that, even if you are not running on Java 5, you can use StringBuffer in place of StringBuilder. The joining of String has got even easier in JDK 8, where you have got the join() method right in the String class itself. The join() method takes a delimiter and a source, which can be an array or collection, and returns a String where each element is joined by a delimiter.

Overriding equals() and hashCode() method in Java and Hibernate

Override equals and hashCode in Java

Equals and hashCode in Java are two fundamental methods that are declared in Object class and part of the core Java library. equals() method is used to compare Objects for equality while hashCode is used to generate an integer code corresponding to that object. equals and hashCode have been used extensively in Java core library like they are used while inserting and retrieving Object in HashMap, see how to get method of HashMap works in Java for the full story, equals method is also used to avoid duplicates on HashSet and other Set implementation and every other place where you need to compare Objects.

Difference between map() and flatMap() in Java 8 Stream - Example

The map() and flatmap() are two important operations in the new functional Java 8. Both represent functional operation and they are also methods in java.util.stream.Stream class but the map is used for transformation and flatmap is used for both transformation and flattening, that's why it's called the flatmap. The key difference between map() and flatmap() function is that when you use a map(), it applies a function on each element of the stream and stores the value returned by the function into a new Stream. This way one stream is transformed into another like a Stream of String is transformed into a Stream of Integer where each element is the length of the corresponding Stream.

10 Example of Lambda Expressions and Streams in Java 8

Java 8 release is just a couple of weeks away, scheduled on 18th March 2014, and there is a lot of buzz and excitement about this path-breaking release in the Java community. One feature, which is synonymous with this release is lambda expressions, which will provide the ability to pass behaviors to methods. Prior to Java 8, if you want to pass behavior to a method, then your only option was the Anonymous class, which will take 6 lines of code, and the most important line, which defines the behavior is lost in between. Lambda expression replaces anonymous classes and removes all boilerplate, enabling you to write code in a functional style, which is sometimes more readable and expression.

5 Difference between Constructor and Static Factory method Pattern in Java

The common way to create objects in Java is by using public constructors. A class provides a public constructor like java.lang.String so anyone can create an instance of String class to use in their application, but, there is another technique that can be used to create objects in Java and every experienced Java programmer should know about it. A class can provide a public static factory method that can return an instance of the class e.g. HashMap.newInstance(). The factory method is a smart way to create objects in Java and provides several advantages over the traditional approach of creating objects using constructors in Java. It can also improve the quality of code by making the code more readable, less coupled, and improves performance by caching.

How to set Java Path and Classpath in Windows 7, 8 and Windows 10 - Tutorial

So, you just bought a new PC or Laptop with Windows 8 operating system, and wondering how to set PATH and Classpath on Windows 8; Or, you might have just upgraded your Windows 7 laptop to the professional edition of Windows 8 and looking to set JDK Path to compile Java programs. Not to worry, this is the second step for anyone who wants to learn Java programming. Of course, the first step is to install JDK.  In this Java tutorial, we will see step by step guide to set Java PATH and CLASSPATH in the Windows 8 operating system. By the way, if you are learning Java in Windows 10 operating system, You should still be able to set the Java path and classpath in Windows 10 by following the steps given here, because navigation steps for modifying environment variables on Windows 10 and Windows 8 are almost same.

Difference between @WebMvcTest and @DataJpaTest in Spring Boot? Example

Hello guys, testing the Spring Boot application is very important but not many developers pay attention to that. If you are learning how to test the Spring Boot application and wondering what is @WebMvcTest and @DataJpaTest and how to use them then you have come to the right place. Earlier, I have shared 20+ Spring Boot Testing interview questions and in this article, I will teach you how to use @DataJpaTest and @WebMvcTest annotation with real-world examples.  Spring Boot is an evolution of the Spring framework which helps to create both stand-alone and spring-based applications with minimal cost. 

How to remove all special characters from String in Java? Example Tutorial

You can use a regular expression and replaceAll() method of java.lang.String class to remove all special characters from String. A special character is nothing but characters like - ! #, %, etc. Precisely, you need to define what is a special character for you. Once you define that you can use a regular expression to replace those characters with empty String, which is equivalent to removing all special characters from String. For example, suppose, your String contains some special characters e.g. "Awesome!!!" and you want to remove those !!! to reduce some excitement, you can use replaceAll("!", "") to get rid of all exclamation marks from String.

Difference between Comparison (QuickSort) and Non-Comparison (Counting Sort) based Sorting Algorithms? Example

For many of you, this might be a surprise that how you can sort or arrange items without comparing them with each other, but it's possible. There are some sorting algorithms that perform sorting without comparing the elements rather than making certain assumptions about the data they are going to sort. The process is known as non-comparison sorting and algorithms are known as the non-comparison-based sorting algorithms. Non-comparison sorting algorithms include Counting sort which sorts using key-value, Radix sort, which examines individual bits of keys, and Bucket Sort which examines bits of keys. These are also known as Liner sorting algorithms because they sort in O(n) time. They make certain assumptions about data hence they don't need to go through a comparison decision tree.

Why Static Code Analysis is Important? Pros and Cons

In the last few years, Software code quality and security have gone from being a “nice to have” to a necessity, and many organizations, including investment banks, are making it mandatory to pass static code analysis tests, penetration testing, and security testing before you deploy your code in production. Static analysis tools like findbugs and fortify are getting popular every passing day and more and more companies are making fortify scan mandatory for all new development.  For those unaware of what static code analysis is, static code analysis is about analyzing your source code without executing them to find potential vulnerabilities, bugs, and security threats.

How to Read/Write from RandomAccessFile in Java - Example Tutorial

Random access file is a special kind of file in Java that allows non-sequential or random access to any location in the file. This means you don't need to start from 1st line if you want to read line number 10, you can directly go to line 10 and read. It's similar to the array data structure, Just like you can access any element in the array by index you can read any content from the file by using a file pointer. A random-access file actually behaves like a large array of bytes stored in the file system and that's why it's very useful for low latency applications which need some kind of persistence e.g. in front office trading application and FIX Engine, you can use random access file to store FIX sequence numbers or all open orders.

Difference between JAX-RS, Restlet, Jersey, RESTEasy, and Apache CXF Frameworks

The JAX-RS is a Java specification request (JSR 311 & JSR 339) that standardizes the development and deployment of RESTful web services using Java and JEE technologies. It provides API in Java Programming language to create web services according to the REST (Representational State Transfer) architectural pattern. Both Restlet and Jersey are two of the most popular implementation of JAX-RS used for developing RESTful web services in Java ecosystem but there is a couple of other implementation also exist like Apache Wink, Apache CXF, and JBoss RESTEasy, along with omnipresent and the most popular option of creating REST web services with Spring Framework, Spring Boot, and Spring MVC. 

How to compare objects on natural order in Java? Comparable + compareTo Example

Java allows you to sort your object in natural order by implementing a Comparable interface. It's one of the fundamental interfaces of Java API and is defined in java.lang package, which means you don't need to implement this unlike its counterpart Comparator, which is defined in java.util package.  Comparable is used to provide natural order of sorting to objects e.g. numeric order is a natural order for numbers, alphabetic order is a natural order for String and chronological order is natural for dates. Similarly when you define your own objects like Person, Book, or Employee, sorting them by name sounds natural. Similarly, for teams, ranking seems their natural order. It all depends on how the object is looked into in its domain.

Difference between Association, Composition and Aggregation in Java, UML and Object Oriented Programming

In Object-oriented programming, one object is related to another to use functionality and service provided by that object. This relationship between two objects is known as the association in object-oriented general software design and is depicted by an arrow in Unified Modelling Language or UML. Both Composition and Aggregation are the forms of association between two objects, but there is a subtle difference between composition and aggregation, which is also reflected by their UML notation. We refer to the association between two objects as Composition when one class owns other classes and other classes can not meaningfully exist, when the owner is destroyed.

How to Filter Stream and Collections in Java 8? Example Tutorial

Java 8 provides excellent features to support the filtering of elements in Java Collections. Prior to Java 8, the only better way to filter elements is by using a foreach loop or iterating over Collection using the Iterator and selecting the required object, leaving out rest. Though that approach work, it was very difficult to run them in parallel and take advantage of multiple CPUs available in modern-day servers. Java 8 provides Streams, which not only makes it easy to run any operation parallel but also supports lazy loading and lazy evaluation, which means as soon as the filtering condition is satisfied, it stooped doing work, doesn't matter how many objects the collection contains.

StringTokenizer Example in Java with Multiple Delimiters - Example Tutorial

StringTokenizer is a legacy class for splitting strings into tokens. In order to break String into tokens, you need to create a StringTokenizer object and provide a delimiter for splitting strings into tokens. You can pass multiple delimiters e.g. you can break String into tokens by, and: at the same time. If you don't provide any delimiter then by default it will use white-space. It's inferior to split() as it doesn't support regular expression, also it is not very efficient. Since it’s an obsolete class, don't expect any performance improvement either. On the hand split() has gone some major performance boost on Java 7, see here to learn more about splitting String with regular expression.

5 ways to check if String is empty in Java - examples

String in Java is considered empty if it's not null and its length is zero. By the way, before checking length you should verify that String is not null because calling length() method on null String will result in java.lang.NullPointerException. Empty String is represented by String literal “”. The definition of empty String may be extended to those String as well which only contains white space but it's a specific requirement and in general String with white space is not considered as empty String in Java. Since String is one of the most frequently used classes and commonly used in method arguments, we often need to check if String is empty or not. Thankfully there are multiple ways to find if String is empty in Java or not.

Difference between for loop and Enhanced for loop in Java? Example Tutorial

Though you can use both for loop and enhanced for loop to iterate over arrays and collections like a list, set, or map. There are some key differences between them. In general, enhanced for loop is much easier to use and less error-prone than for loop, where you need to manage the steps manually. At the same time, for loop is much more powerful because you get the opportunity to control the looping process. All the differences, you will learn in this article, stems from the very fact that traditional for loop gives more control than enhanced for loop but on the other hand enhanced or advanced for loop gives more convenience.

What is difference between Maven, ANT, Jenkins and Hudson?

In short, though Maven and ANT are build tools the main difference is that maven also provides dependency management, standard project layout, and project management. On the difference between Maven, ANT, and Jenkins, later is a continuous integration tool which is much more than a build tool. You can set up your CI environment using Jenkins or Hudson and automatically build, test, and deploy your Java project. Now last, the main difference between Jenkins and Hudson, both originate from the same source code but one is a closed source while the other is open source. You can read the details in this article.

Difference between OCPJP 8 Upgrade Exams 1Z0-813 and 1Z0-810? Which one to take?

Many Java developers who hold a Java certification either from Sun or Oracle and who are looking to upgrade to the latest Java version i.e. Java SE 8 certification have a common doubt, should they go for 1Z0-810 or 1Z0-813 upgrade exams? What are the differences between these two exams? Well, even though they are both upgrades to Java SE 8 exams, they are separate exams and have a different exam code, the difference is also obvious when you look at their title. The 1Z0-810 exam is known as "Upgrade Java SE 7 to Java SE 8 OCP Programme" while the 1Z0-813 exam is known as "Upgrade to Java SE 8 OCP ( Java SE 6 and all prior versions)".

5 Free OCEJWCD 6 Mock Exam 1Z0-899 Practice Test

The OCEJWCD is Oracle's version of the SCWCD (Sun Certified Web Component Developer) exam, which tests the candidate's knowledge of Servlet, JSP, and other web technology. The OCEJWCD stands for Oracle Certified Enterprise Java Web Component Developer. Like other Java certifications like the OCAJP or OCPJP, the key to success is selecting a good book, practicing code daily, and then solving as many mock questions as possible.

How to create LocalDateTime in Java 8 - Example Tutorial

The LocalDateTime is a new class introduced in Java 8 new Date and Time API. This class is in java.time package and it represents both date and time information without timezone. In this example, you will learn different ways to create an instance of LocalDateTime class in Java 8 like by using the static factory method, or by combining LocalDate and LocalTime instances together, which are subsequently used to denote date without time and time without the date in Java 8. As their name suggests they are local, so they don't contain timezone information.

3 ways to loop over Set or HashSet in Java? Examples

Since Set interface or HashSet class doesn't provide a get() method to retrieve elements, the only way to take out elements from a Set is to iterate over it by using the Iterator, or loop over Set using advanced for loop of Java 5. You can get the iterator by calling the iterator() method of the Set interface. This method returns an iterator over the elements in the sets but they are returned in no particular order, as Set doesn't guarantee any order. Though individual Set implementations e.g. LinkedHashSet or TreeSet can impose ordering and in such iterator will return elements on that order.

Java Comparator Example for Custom Sorting Employee by Name, Age and Salary

In this tutorial, we will see the Java Comparator example to sort an Employee object by name, age, and salary. In order to sort Employee object on different criteria, we need to create multiple comparators e.g. NameComparator, AgeComparator, and SalaryComparator, this is known as custom sorting in Java. This is different from the natural ordering of objects, provided by the compareTo() method of java.lang.Comparable interface. Though both compare() and compareTo() method looks similar they are different in the sense that, former accepts one parameter, while later accepts two-parameter. Former compare passed object to the current object, on the other hand, compare() method compares two different objects passed to it.

How to use Lambda Expression in Place of Anonymous Class in Java 8 - Example Tutorial

Before Java 8, the Anonymous class was the only way you can implement functional idioms in Java. Since prior to Java 8 you cannot pass a function to another function, you would have to wrap it into an object, as seen in Strategy Pattern. Those are also known as function objects in Java. Anonymous class was also handy to create a throw-away implementation of SAM (Single Abstract Methods) interfaces like Runnable, Callable,  CommandListener, or ActionListener. Despite all these goodies and flexibility, the Anonymous class adds too much boilerplate code, making it hard to read and understand.

Reading/Writing to/from Files using FileChannel and ByteBuffer in Java - Example Tutorial

In the past, I have talked about RandomAccessFile and how it can be used for doing faster IO in Java, and in this Java NIO tutorial, we are going to see how to use read/write data from using FileChannel and ByteBuffer. Channel provides an alternate way to read data from a file, it provides better performance than InputStream or OutputStream. It can also be opened in blocking and non-blocking mode. Though FileChannles are read/write channels and they are always blocking, they cannot be put into non-blocking mode.

Top 5 Blogs Java EE developers should follow

One reason for Java's great success as a programming language is that it has dominated the Enterprise space. Earlier J2EE used to be the popular platform, but now we have a more modern and improved Java EE platform, with the latest release of Java EE 7. Java Platform, Enterprise Edition 7 provides new features that include enhanced HTML5 support, increases developer productivity, and further improves how enterprise demands can be met. One of the biggest advantages of Java EE 7 is the reduction of boilerplate code.

10 Difference between Primitive and Reference variable in Java - Example Tutorial

There are two types of variables in Java, primitive and reference type. All the basic types e.g. int, boolean, char, short, float, long and double are known as primitive types. JVM treats them differently than reference types, which is used to point objects e.g. String, Thread, File, and others. Reference variables are not pointers but a handle to the object which is created in heap memory. The main difference between primitive and reference type is that primitive type always has a value, it can never be null but reference type can be null, which denotes the absence of value. So if you create a primitive variable of type int and forget to initialize it then it's value would be 0, the default value of integral type in Java, but a reference variable by default has a null value, which means no reference is assigned to it.

Adapter vs Decorator vs Facade vs Proxy Design Pattern in Java

There is some striking similarity between Adapter, Decorator, Facade, and Proxy design patterns, in the sense that they all use Composition and delegation to solve the problem. The adapter pattern wraps an interface, and delegates call to it. The decorator wraps an object and implements behavior on top of that, Facade wraps one or more interfaces to provide a central interface, which is easy to use and Proxy Pattern also wraps Subject and delegates calls to it. Then questions come, why are different patterns? What is the difference between Adapter, Decorator, Facade, or Proxy pattern, if their structure is the same. The answer is Intent. Yes, all of these Java design patterns have similar structure and class diagrams but their intents are totally different from each other.

Difference between extends and implements keywords in Java? Example Tutorial

Though both extends and implements keyword in Java is used to implement Inheritance concept of Object-Oriented programming, there is a subtle difference between them. The extends keyword is mainly used to extend a class i.e. to create a subclass in Java, while the implements keyword is used to implement an interface in Java. The extends keyword can also be used by an interface for extending another interface. In order to better understand the difference between extends and implements, you also need to learn and understand the difference between class and interface in Java.

Why Default or No Argument Constructor is Important in Java Class? Answer

Almost all Java developers know that compiler adds a default constructor or better known as a no-argument constructor in every Java class, but many of them forget that it only does when you don't provide any other constructor. This means it becomes the developers' responsibility to add a no-argument constructor if he is adding an explicit constructor. Now, Why it's important to provide a default constructor in Java, What happens if your class doesn't have a no-argument constructor? Well, this is how it's asked in many Java interviews, most commonly as part of Spring and Hibernate interviews.

3 Ways to Convert Java 8 Stream to an Array - Lambda Expression and Constructor Reference Example

One of the frequently asked Java 8 interview questions is, how you do convert a Java 8 Stream to an array? For example, you have a Stream of Strings and you want an array of String so that you can pass this to a legacy method that expects an array, how do you do that? Well, the obvious place to search is the Javadoc of java.util.stream.Stream class and there you will find a toArray() method. Though this method will convert the Stream to an array it has a problem, it returns an Object array. What will you do, if you need a String array? Well, you can use the overloaded version of the toArray(IntFunction generator), which expects a generator function to create an array of the specified type.

2 solution of java.lang.OutOfMemoryError in Java

Everyone in java development faces java.lang.OutOfMemoryError now and then, OutOfMemoryError in Java is one problem which is more due to the system's limitation (memory) rather than due to programming mistakes in most cases though in certain cases you could have a memory leak which causing OutOfMemoryError. I have found that even though java.lang.OutOfMemoryError is quite common basic knowledge of its cause and the solution is largely unknown among junior developers. Beginners books like Head First Java don't teach you much about how to deal with this kind of error. You need real experience dealing with production systems, handling a large number of user sessions to troubleshoot and fix performance issues like running out of memory.

How to enable SSL debugging in Java JVM? Example

Dealing with SSL issues in Java web applications is no fun, especially when you have no debug or troubleshooting logs and all you see is an ugly ‘Page Cannot be displayed error message in your browser. Thankfully you can easily enable SSL to debug on your Application to start seeing verbose logs that will clearly show what happens during the SSL handshake process.

Top 5 Java 8 Practice Test and Exam Simulators (OCAJP and OCPJP) - Best of lot

Apart from books, exam simulators are another essential tool to prepare for Java certifications. They not only give you the opportunity to test your knowledge topic-wise but also provide a helpful explanation to clear your doubt and misconception, which means you can learn on the fly. Actually, when I prepared for my SCJP exam, I learned a lot of new concepts by just giving mock exams and solving practice questions. Since most of the Java certification aspirants are Java developers with some experience i.e., they have done a good amount of coding, they can easily understand the code, but they might not be familiar with the exam format.

How to convert java.util.Date to java.sql.Timestamp? Example Tutorial

You can convert a java.util.Date to java.sql.Timestamp value by using the getTime() method of Date class. This method returns the long millisecond value from Epoch (1st January 1970 midnight) which you can pass to java.sql.Timestamp to create a new instance of Timestamp object in JDBC. Remember, java.sql.TimeStamp class is a wrapper around java.util.Date to allow JDBC to view it as SQL TIMESTAMP value. The only way to create a Timestamp instance is by passing the long time value because the second constructor of the Timestamp class, which accepts individual fields like a year, month, date, hour, minute, second, and nano is deprecated. Timestamp class can also hold up to nanosecond value.

How to get the last modified date and time of a File or Directory in Java? Example Tutorial

Sometimes before processing a file, you want to check its last modified date to avoid processing an old file. Though some programmers prefer to attach the date in the file name itself, I don't find it a cleaner approach. For example, suppose you are downloading closing prices of stocks and processing them at the start of the day, and loading them into the database. In order to accidentally process an old file, you can check the last modified date before processing and if it's in the acceptable range, you can process the file. You can get the last modified date of a file in Java by using java.io.File class. 

How to create RESTful Web Services using Restlet Framework in Java - Example Tutorial

Hello Java developer, if you are looking for an example of how to create RESTful web services using Restlet Framework in Java and Eclipse then you have come to the right place. Earlier, I have shared the best REST API Courses and in this tutorial, I will show you how to use Restlet for creating REST APIs in Java. The Restlet is one of the first open-source frameworks to create and deploy RESTful web services in Java. After the release of JAX-RS (Java API for RESTful Web Services) JSR - 317, Restlet also supports JAX-RS annotation and provides a consistent way to create both RESTful Server and Client. HelloWorld program is the traditional way to start with new technology and continuing to the tradition, we'll write our first Restlet program as HelloWorld. 

Difference between GETDATE() vs SYSDATETIME() vs GETUTCDATE() in SQL Server - Examples

One of the common questions on the Microsoft SQL Server interview is, what is the difference between GETDATE(), SYSDATETIME(), and GETUTCDATE(). Even though all three SQL Server function returns the current date-time in SQL Server, there are some subtle differences between them. The main difference between GETDATE() and SYSDATETIME() is that GETDATE returns the current date and time as DATETIME but SYSDATETIME returns a DATETIME2 value, which is more precise.

Difference between PUT and POST in REST Web Services in Java - Example

If you remember REST WebServices uses HTTP methods to map CRUD (create, retrieve, update, delete) operations to HTTP requests. Even though both PUT and POST methods can be used to perform create and update operations in REST WebServices, Idempotency is the main difference between PUT and POST. Similar to the GET request, the PUT request is also idempotent in HTTP, which means it will produce the same results if executed once more multiple times. Another practical difference between PUT and POST methods in the context of REST WebService is that POST is often used to create a new entity, and PUT is often used to update an existing entity.

How to replace a substring in Java? String replace() method Example Tutorial

You can replace a substring using replace() method in Java. The String class provides the overloaded version of the replace() method, but you need to use the replace(CharSequence target, CharSequence replacement). This version of the replace() method replaces each substring of this string (on which you call the replace() method) that matches the literal target sequence with the specified literal replacement sequence. For example, if you call "Effective Java".replace("Effective", "Head First") then it will replace "Effective" with "Head First" in the String "Effective Java". Since String is Immutable in Java, this call will produce a new String "Head First Java".

How to check if ResultSet is empty in JDBC Java - Example Tutorial

The JDBC ResultSet doesn't provide any isEmpty(), length() or size() method to check if its empty or not. Hence, when a Java programmer needs to determine if ResultSet is empty or not, it just calls the next() method and if next() returns false it means ResultSet is empty. This is correct but the main problem with this approach is if the ResultSet is not empty then you may miss the first row if you follow the standard idiom to iterate over ResultSet and get the rows that involve calling the next() method of ResultSet in a while loop.

5 ways to add multiple JAR in to Classpath in Java - Examples

How to add the JAR file to Classpath in Java

Adding JAR into classpath is a common task for Java programmers and different programmers do it in different ways. Since Java allows multiple ways to include JAR files in the classpath, it becomes important to know the pros and cons of each approach and How exactly they work. There are 5 ways to add jars into classpath in Java some of them we have already seen in  How classpath works in Java and How to set Path in Java. In this post, we will revisit some of those techniques and explore Java 1.6 wildcard to add multiple JAR into the classpath. 

How to implement Post Order Traversal of Binary Tree in Java - Recursion and Iteration Example

This is the third article on tree traversal. In the last couple of articles, I have shown you how to implement preorder and inorder traversal in Java, both recursively and iteratively and today, you will learn about the post-order traversal. Out of these three main tree traversal algorithms, the post-order traversal is most difficult to implement, especially the iterative version. In postorder traversal, you first visit left subtree, then right subtree and at last you print the value of root or not. So, the value of root is always printed at last in the post-order traversal.

Java Enum Tutorial: 10 Examples of Enum in Java

What is Enum in Java
Enum in Java is a keyword, a feature that is used to represent a fixed number of well-known values in Java, For example, Number of days in the Week, Number of planets in the Solar system, etc. Enumeration (Enum) in Java was introduced in JDK 1.5 and it is one of my favorite features of J2SE 5 among Autoboxing and unboxing, Generics, varargs, and static import. One of the common use of Enum which emerged in recent years is Using Enum to write Singleton in Java, which is by far the easiest way to implement Singleton and handles several issues related to thread-safety and Serialization automatically. 

Top 10 Excuses Programmers Gives to Avoid Unit Testing

Though everyone loves unit tests and everyone agrees with the benefits they bring in, when the time comes to write them, you will see a lot of excuses, even from some of the more experienced and senior developers. At the heart of the problem of not writing unit tests or enough unit tests are two things, first is time pressure i.e. you don't have enough time to complete coding forget about writing unit tests. This problem comes due to erroneous estimation i.e. only estimating time for coding and not including unit testing as part of development.

How to Implement Binary Search Tree in Java? Example

A binary search tree or BST is a popular data structure that is used to keep elements in order. A binary search tree is a binary tree where the value of a left child is less than or equal to the parent node and the value of the right child is greater than or equal to the parent node. Since it's a binary tree, it can only have 0, 1, or two children. What makes a binary search tree special is its ability to reduce the time complexity of fundamental operations like add, remove, and search, also known as insert, delete and find. In a BST, all these operations (insert, remove, and find) can be performed in O(log(n)) time.

What is @SuppressWarnings annotation in Java? Unchecked, RawTypes, Serial Example

@SuppressWarnings annotation is one of the three built-in annotations available in JDK and added alongside @Override and @Deprecated in Java 1.5. @SuppressWarnings instruct the compiler to ignore or suppress, specified compiler warning in annotated element and all program elements inside that element. For example, if a class is annotated to suppress a particular warning, then a warning generated in a method inside that class will also be separated. You might have seen @SuppressWarnings("unchecked") and @SuppressWarnings("serial"), two of most popular examples of @SuppressWarnings annotation. Former is used to suppress warning generated due to unchecked casting while the later warning is used to remind about adding SerialVersionUID in a Serializable class.

How to Code in Dart Programing language? Dart Hello World Example Tutorial

Google Datt is a general-purpose programming language from Google and is used to build web applications, mobile applications, and the Internet of Things (IoT).  Its most popular application is in Flutter framework, which is Google's mobile app SDK for crafting high-quality native interfaces on iOS and Android in record time. If you haven't tried it yet then it's a good time to try it and see how much it offers to a programmer and whether it is a suitable language to replace JavaScript or not. 

Inner class and nested Static Class in Java with Example

Inner class and nested static class in Java both are classes declared inside another class, known as top level class in Java. In Java terminology, If you declare a nested class static, it will called nested static class in Java while non-static nested classes are simply referred as Inner Class. Inner classes are also a popular topic in Java interviews. One of the popular questions is the difference between inner class and nested static class , some time also referred to as a difference between static and non static nested class in Java. One of the most important questions related to nested classes are Where should you use nested class in Java?

How to Attach Source Code in Eclipse to JAR Files for Debugging and Navigation With JDK Example

Attaching the source of any Jar in Eclipse e.g. JDK or open-source libraries like Spring framework is a good idea because it helps during debugging and code development. As a Java programmer at least you should attach the source of JDK in Eclipse IDE to find out more about JDK classes. Though Eclipse IDE is pretty good on code assist, sometimes You want to know what's going inside a library or a JDK method, rather than just reading the documentation. Interview questions like How HashMap works in Java or How substring causes memory leak can only be answered if you are familiar with the source code of these classes.  

How to Compare Arrays in Java – Equals vs deepEquals Example

java.util.Arrays class provides equals() and deepEquals() method to compare two Arrays in Java. Both of these are overloaded methods to compare primitive arrays e.g. int, long, float, double, and Object arrays e.g. Arrays.equals(Object[], Object[]). Arrays.equals() returns true if both Arrays which it is comparing are null If both arrays pointing to the same Array Object or they must be of the same length and contains the same element in each index. In all other cases, it returns false. Arrays.equals() calls equals() method of each Object while comparing Object arrays.