Java 8 Stream filter() + findFirst Example Tutorial

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 22 Array Concepts Interview Questions Answers in Java

An array is one of the fundamental data structures and most of the other advanced data structures like lists, hash tables are built using arrays.  Good knowledge of fundamental data structures like the array, linked list, a binary tree is not just essential for writing better code but also doing well on Programming Job interviews. Array-based questions are quite popular in Java interviews. There are two types of questions you will find, first which are based upon array implementation in Java, and second which are based upon how to use an array data structure to solve some coding problems. The first type of question is quite popular in the telephonic round of Java interviews and the second is usually asked on written tests and face-to-face interviews.

How to add and remove Elements from an Dynamic Array in Java? Example Tutorial

Java beginners often ask how to add new elements to an array in Java? 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. This means neither you can add new elements nor you can remove an old one from an array in Java. All you can do is reassign values to a different bucket. For example, if you have a string array of length 3 like {"java", "is", "great"} then you can just replace the individual index to make it like {"Python", "is", "great"} by replacing "java" with "Python" at first index, but you cannot add or remove elements.

How to Remove Objects From ArrayList while Iterating in Java - Example Tutorial

One of the common problems many Java Programmers face is to remove elements while iterating over ArrayList in Java because the intuitive solution doesn't work like you just cannot go through an ArrayList using a for loop and remove an element depending upon some condition. Even though java.util.ArrayList provides the remove() methods, like remove (int index) and remove (Object element), you cannot use them to remove items while iterating over ArrayList in Java because they will throw ConcurrentModificationException if called during iteration. The right way to remove objects from ArrayList while iterating over it is by using the Iterator's remove() method.

9 JSP Implicit Objects and When to Use Them

If you are new to JSP then your first question would be what are implicit objects in JSP? Well, implicit objects in JSP are Java object which is created by Servlet containers like the tomcat or Jetty during translation phase of JSP, when JSP is converted to Servlet. These objects are created as local variables inside the service() method generated by the container. The most important thing about the implicit objects is to remember that these objects are available to any JSP developer inside the JSP page and they can do a lot of things with implicit objects and expression language which was only possible with scriptlet earlier. That's why they are known as implicit objects. 

How to implement PreOrder traversal of Binary Tree in Java - Example Tutorial

The easiest way to implement the preOrder traversal of a binary tree in Java is by using recursion. The recursive solution is hardly 3 to 4 lines of code and exactly mimic the steps, but before that, let's revise some basics about a binary tree and preorder traversal. Unlike array and linked list which have just one way to traverse, I mean linearly, the binary tree has several ways to traverse all nodes because of its hierarchical nature like level order, preorder, postorder, and in order. Tree traversal algorithms are mainly divided into two categories, the depth-first algorithms, and breadth-first algorithms. In depth-first, you go deeper into a tree before visiting the sibling node, for example, you go deep following the left node before you come back and traverse the right node.

How to reverse a singly linked list in Java without recursion? Iterative Solution Example

Hello guys, reverse a linked list is a common coding problem from Programming Job interviews and I am sure you have seen this in your career, if you are not, maybe you are a fresher and you will going to find about this very soon in your next technical interview. In the last article, I have shown you how to use recursion to reverse a linked list, and today, I'll show you how to reverse a singly linked list in Java without recursion. A singly linked list, also known as just linked list is a collection of nodes that can only be traversed in one direction like in the forward direction from head to tail. Each node in the linked list contains two things, data and a pointer to the next node in the list.

How to use Randam vs ThreadLocalRandom vs SecureRandom in Java? Example Tutorial

Hello guys, one of the common tasks for Java developers is to generate an array of random numbers, particularly in game development. For example, if you are coding for dice-based games like Ludo or Snake and Lader then you need to generate a random number from 1 to 6 to simulate dice behavior. The same goes for other dice-based games. There are many cases where you need to generate random numbers and an array of random numbers. In some cases, duplicates may be allowed while other duplicates are not permitted.  

How to implement Linear Search Algorithm in Java? Example tutorial

In the last article about searching and sorting, you have learned the binary search algorithm and today I'll teach you another fundamental searching algorithm called Linear search. Linear search is nothing but iterating over the array and comparing each element with the target element to see if they are equal since we search the array sequential from start to end, this is also known as sequential search or linear search. It is very slow as compared to binary search because you have to compare each element with every other element and is definitely not suitable for a large array. It's practically useful only in the case of a small array of up to 10 to 15 numbers. In the worst case, you need to check all elements to confirm if the target element exists in an array or not.

How to Convert String to LocalDateTime in Java 8 - Example Tutorial

Hello guys, today, I will talk about a common problem while working in a Java application, yes you guessed it right, I am talking about String to Date conversion in Java. I had discussed this before (see the Date to String) when Java 8 was not out, but with Java 8, I don't see any reason to use old date and time API, and hence I am writing this post to teach you how to convert String to Date in Java 8 or beyond. Suppose you have a date-time String "2016-03-04: 11:01:20" and you want to convert this into a LocalDateTime object of Java 8 new date and time API, how do you do that? Well, if you have worked previously with String and Date then you know that you can parse String to Date in Java.

How to use Stream.filter method in Java 8? Example Tutorial

In the last couple of Java 8 tutorials, you have learned how to use map(), flatMap(), and other stream methods to get an understanding of how Java 8 Stream and Lambda expressions make it easy to perform the bulk data operation on Collection classes like List or Set. In this Java 8 tutorial, I am going to share how to use the filter() method in Java 8, another key method of the Stream class.  This is the one method you will always be used because it forms the key part of the Stream pipeline. If you have seen some Java 8 code, you would have already seen this method a couple of times.

How to reverse bits of an integer in Java? [LeetCode Solution]

Hello guys In this Java article, you will learn how to reverse bits of an integer in Java. This is one of the common coding problems which is often asked during phone rounds of technical interviews on companies like Amazon, Google, and Microsoft. If you have appeared in any programming interviews then there is a good chance that you might have already seen this problem before. If you know the solution then you are in a good place but if you don't know the solution then don't disappoint as many experienced Java developers also struggle to solve this problem.

10 Examples of Stream API in Java 8 - count + filter + map + distinct + collect() Examples

The Java 8 release of Java Programming language was a game-changer version. It not only provided some useful methods but totally changed the way you write programs in Java. The most significant change it brings in the mindset of Java developers was to think functional and supported that by providing critical features like lambda expression and Stream API, which takes advantage of parallel processing and functional operations like filter, map, flatMap, etc. Since then, a lot of Java developers are trying their hands to learn those significant changes like lambda expression, method reference, new Date and Time classes, and, more importantly, Stream API for bulk data operations.

How to debug Java 8 Stream Pipeline - peek() method Example Tutorial

Hello guys, I have been writing about some important methods from Java SE 8  like map(), flatMap(), collect(), etc for quite some time, and today I'll share my experience with another useful method peek() from java.utill.stream.Stream class. The peek() method of the Stream class can be very useful to debug and understand streams in Java 8. You can use the peek() method to see the elements as they flow from one step to another like when you use the filter() method for filtering, you can actually see how filtering is working like lazy evaluation as well as which elements are filtered.

Can you make an Abstract Class or Method Final in Java? Example

No, you cannot make an abstract class or method final in Java because the abstract and final are mutually exclusive concepts. An abstract class is incomplete and can only be instantiated by extending a concrete class and implementing all abstract methods, while a final class is considered complete and cannot be extended further. This means when you make an abstract class final, it cannot be extended hence it cannot be used and that's why the Java compiler throws a compile-time error when you try to make an abstract class final in Java. In short, an abstract class cannot be final in Java, using both abstract and final modifiers with a class is illegal in Java. 

How to Calculate Next Date and Year in Java | LocalDate and MonthDay Example Tutorial

Hello guys, if you are wondering how to calculate the next premium date, next birthday, or exact date for the next Christmas holiday in Java then you have come to the right place. Earlier, I have shared 20+ examples of Date and Time in Java, and in this article, I will show you how you can use the LocalDate and MonthDay class from the new Java 8 Date and Time package to calculate the next or previous date in Java. This new API is very well structured and you have classes to represent different Date concepts, for example, you can use LocalDate to represent a Date without time components like the next premium date or employee joining date or birth date. 

How to Reverse an Array in place in Java? Example Solution

It's relatively easy to reverse an array if you have the luxury to use another array, but how would you reverse an array if a temporary buffer is not allowed? This is one of the testing array interview questions, which often proved tricky for Java and other beginner Programmers. But, don't worry, I'll tell you how you can solve this problem without losing your cool. Well, you can also reverse an array in place without using an additional buffer. If you know how to access array elements and how to loop over an array in Java using traditional for loop, you can easily solve this problem without using additional space or in-place as described in many Algorithms books and courses, and on Coding interviews.

3 ways to ignore null fields while converting Java object to JSON using Jackson? Example

Ignoring null fields or attribute is a one of the common requirement while marshaling Java object to JSON string because Jackson just prints null when a reference filed is null, which you may not want. For example, if you have a Java object which has a String field whose value is null when you convert this object to Json, you will see null in front of that. In order to better control JSON output, you can ignore null fields, and Jackson provides a couple of options to do that. You can ignore null fields at the class level by using @JsonInclude(Include.NON_NULL) to only include non-null fields, thus excluding any attribute whose value is null.

5 Differences between an array and linked list in Java

The difference between an array and a linked list is one of the frequently asked data structure and algorithm interview questions and you might have seen it before on your telephonic or face-to-face interview. It is also a very popular question during practical exams in Computer Science degree courses like B.E. and B.Tech. It's very simple and easy to answer but you just can't afford to miss this question in an interview. Both array and linked list are two of the most popular and fundamental data structures in Computer Science and Programming, and Java supports both of them.

What is difference between final vs finally and finalize in Java?

Hello guys, final, finally, and finalize are three confusing keywords, modifiers, and methods in Java. They sound similar, but they are for different purposes. 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 like String is final in Java. When you use the final modifier with a method, then 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.

How to convert ArrayList to HashMap and LinkedHashMap in Java 8 - Example Tutorial

One of the common tasks in Java is to convert a List of objects, like a List<T> into a Map, I mean Map<K, V>, where K is some property of the object and V is the actual object. For example, suppose you have a List<Order>, and you want to convert it into a Map, e.g. Map<OrderId, Order>, how do you that? Well, the simplest way to achieve this is iterating over List and add each element to the Map by extracting keys and using the actual element as an object. This is exactly what many of us do in the pre-Java 8 world, but JDK 8 has made it even simpler.

How to code Binary Search Algorithm using Recursion in Java? Example

Hello guys, In the last article, we have seen the iterative implementation of binary search in Java, and in this article, you will learn how to implement binary search using recursion. Recursion is an important topic for coding interviews but many programmers struggle to code recursive solutions. I will try to give you some tips to come up with recursive algorithms in this tutorial. In order to implement a recursive solution, you need to break the problem into sub-problems until you reach a base case where you know how to solve the problem like sorting an array with one element. Without a base case, your program will never terminate and it will eventually die by throwing the StackOverFlowError.

Post Order Binary Tree Traversal in Java Without Recursion - Example Tutorial

In the last article, I have shown you how to implement post-order traversal in a binary tree using recursion, and today I am going to teach you about post order traversal without recursion. To be honest, the iterative algorithm of post-order traversal is the toughest among the iterative pre-order and in-order traversal algorithm. The process of post-order traversal remains the same but the algorithm to achieve that effect is different. Since post-order traversal is a depth-first algorithm, you have to go deep before you go wide. I mean, the left subtree is visited first, followed by the right subtree, and finally, the value of a node is printed.

7 Examples to Sort One and Two Dimensional String and Integer Array in Java | Ascending, Descending and Reverse Order

Sorting array is a day-to-day programming task for any software developer.  If you have come from a Computer Science background then you have definitely learned fundamental sorting algorithms like the bubble sort, insertion sort, and quicksort but you don't really need to code those algorithms to sort an array in Java because Java has good support for sorting different types of array. You can use Arrays.sort() method to sort both primitive and object array in Java. But, before using this method, let's learn how the Arrays.sort() method works in Java. This will not only help you to get familiar with the API but also its inner workings.  This method sorts the given array into ascending order, which is the numeric order for primitives and defined by compareTo() or compare() method for objects.

How to prepare Oracle Certified Master Java EE Enterprise Architect (1z0-807, 1Z0-865, 1Z0-866) - OCMJEA6 Exam

The OCMJEA 6 certification is one of the most difficult, time-consuming, and tiresome Java certifications. Still, it was also the one that made me learn and grow professionally. This certification consists of 5 phases:

Phase 1: Compulsory Course

At this point, the candidate is required to take at least one official Oracle course from Java at any partner company. You can complete this course during certification - before, during, or after.

If you already have experience in Java and architecture, leave to take the course at the end. If not, use the classes to gain knowledge for the test by doing them before. There is a complete grid of Java courses for the candidate to acquire the necessary know-how for this certification.

How to use Record in Java? Example

A Java record is a special kind of java class that is used as a 'data carrier' class without the traditional 'Java ceremony' (boilerplate). This represents an immutable state that is passing immutable data between objects. The Java Record was introduced with Java 14, and it is a preview feature because it must be enabled before it can be used. Records received via a database query, records returned from a remote service call, records read from a CSV file, and other use cases can all benefit from Java Record instances.

How to Check is given String is a Palindrome in Java using Recursion

In this tutorial, you will learn how to check if a string is a palindrome in Java using Recursion. A String is nothing but a collection of characters like "Java," and String literals are encoded in double-quotes in Java. A String is said to be a palindrome if the reverse of String is equal to itself like "aba" is a palindrome because the opposite of "aba" is also "aba", but "abc" is not a palindrome because the reverse of "abc" is "cba" which is not equal. Recursion means solving a problem by writing a function which calls itself. In order to check if String is a palindrome in Java, we need a function that can reverse the String.

Top 5 Free Apache Maven eBooks for Java Developers

If you are working in Java for a couple of years, you surely know about Maven, the most popular tool to build Java applications. Recently I had shared 10 things about Maven Java developers should know, (if you have read it yet, you can read it here) and I receive a lot of good feedback about how useful those plugins and Maven, in general, are for Java developers. This motivated me to write more stuff about Apache Maven, and then I thought about sharing some of the free Maven courses and ebooks Java developers can use to learn Maven. 

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

Hello Guys, if you want to learn SQL Server and looking for free resources then you have come to the right place. Earlier, I have shared free SQL and database courses and today, I am going to share some of the excellent database and SQL server books that 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 significant online and offline library. Many people question me, do I really find to read all the books which I share? Well, I don't read all books page by page, unless and until it's something like Effective Java or Clean Code. 

How to check if strings are rotations of each other in Java? String Rotation Example Solution

String-based algorithmic questions are very popular in Java interviews e.g. checking if two String is the anagram of each other (see), or checking if given String is a palindrome (see), or just finding permutations of given String (see). One of such popular String-based interview questions is about to check if two Strings are a rotation of each other in Java. In order to solve this question, you should know what is String rotation? Well, A string is made of characters and you just rotate the String around any character like "programming" will become "ingprogramm" if we rotate the String on the trailing character 3 times.

4 Best Books to Learn Web Service in Java - SOAP and RESTful

If you are a Java developer and want to learn how to develop Web Services in Java, both SOAP and RESTful, but confused about where to start, then you have come to the right place. In this article, I am going to share some of the best books to learn about both SOAP and RESTful web services in Java. If you are not familiar with Web Services, it's a way to expose the services provided by your application to other developers and applications. For example, if your system offers weather information, then the user can go and check whether manually by looking at the Web GUI built using HTML, CSS, and JavaScript. Still, by exposing the same information using Web services, you allow a programmer to display as they want.

What is the cost of Oracle Java Certifications - OCAJP, OCPJP, OCEWCD, OCPJD?

One of the frequently asked questions about Oracle Java certifications, formerly known as Sun Certified Java programmer like OCAJP, OCPJP, OCEWCD, OCMEJA, etc. is about the cost of certification. Many of my readers often ask what the cost of OCAJP  like OCAJP 8 or OCAJP 11 and  OCPJP like OCPJP 8 and OCPJP 11 is? Is there any discount available? What are the fees of Java 8 certifications? How much Java architect exam cost? Etc. I have answered many of them one to one via Facebook and Email in the past, but after so many such requests, I decided to write a blog post about it.

Top 3 Free Struts Books for Java EE developers - Learn Online, PDF download

Jakarta Struts is one of the most popular MVC frameworks to create a Java web application. Struts 1.0 had ruled the world in the early 2000 era before Spring MVC took over. Still, there are lots of projects written in Struts that need active maintenance, and that's why Struts developers are still in demand. It has not become anything like COBOL, but the latest version of Struts 2.0 is a capable web MVC framework with dependency injection and has a sizable community behind it. It has close competition with Spring MVC, but given the demand for Struts developers, it's still a good technology to learn if you are looking for a job in a Java web development position.

Java Program to find Armstrong numbers with Example

Armstrong number Example in Java
How to check if a number is an Armstrong number or not? or write a Java program to find Armstrong's number? This is a common Java interview question asked on-campus interviews and fresher-level interviews. This is also a popular Java programming exercise on various schools, colleges, and computer courses to build programming logic among Students. An Armstrong number is a 3 digit number for which the sum of cube of its digits is equal to the number itself. 

Insertion Sort Algorithm in Java with Example

Insertion sort is another simple sorting algorithm like Bubble Sort. You may not have realized but you must have used Insertion sort in a lot of places in your life. One of the best examples of Insertion sort in the real-world is, how you sort your hand in playing cards. You pick one card from the deck, you assume it's sorted, and then we insert subsequent cards in their proper position. For example, if your first card is Jack, and the next card is Queen then you put the queen after Jack. Now if the next card is King, we put it after the queen, and if we get 9, we put it before jack.

Difference between VARCHAR and NVARCHAR in SQL Server

Hello guys, if you are confused between VARCHAR and NVARCHAR data types of SQL Server and wondering what is the difference between VARCHAR and NVARCHAR, or you have been asked this question on technical Interviews and you couldn't answer then you have come to the right place. There is a subtle difference between these two character data types in SQL Server, while both supports variable length, the VARCHAR data type is used to store non-Unicode characters while NVARCHAR is used to store Unicode characters. It also takes more space than VARCHAR. 

How to Rotate an Array to Left or Right in Java? Solution Example

Hello guys, welcome to another post with another array-based coding problem. In the last article, we've learned about finding missing numbers in the array with duplicates, and today we'll solve the problem of rotating an array by left or right by a given number. For example, suppose an integer array {1, 2, 3} is given and it was asked to rate this array to the left by 3 then the result array will look like {2, 3, 1} because it was rotated twice on left. Similarly, if you are asked to rotate the same array twice by right then you'll get {1, 2, 3}, the same array is back. 

How to implement Merge Sort Algorithm in Java [Solved] - Example Tutorial

The merge sort algorithm is a divide and conquers algorithm. In the divide and conquer paradigm, a problem is broken into smaller problems where each small problem still retains all the properties of the larger problem -- except its size. To solve the original problem, each piece is solved individually; then the pieces are merged back together. For example, imagine you have to sort an array of 200 elements using the bubble sort algorithm. Since selection sort takes O(n^2) time, it would take about 40,000-time units to sort the array. Now imagine splitting the array into ten equal pieces and sorting each piece individually still using selection sort. Now it would take 400-time units to sort each piece; for a grand total of 10*400 = 4000.

What is Variable and Method Hiding in Java - Example Tutorial

If Java, if you are not careful you can possibly hide both methods and variables of the superclass. Now you must be wondering what does it mean by hiding a variable or method in Java? A field or variable is said to hide all fields with the same name in superclasses. Similarly, a static method with the same name in a subclass can hide the method of the superclass. This can lead to subtle bugs, especially if you are expecting a different method to be called. In this article, I'll show you examples of both variables and methods hiding in Java so that you can understand and avoid them in the future.

How to implement Comparator and Comparable in Java with Lambda Expression & method reference? Example

Hello guys, After Java 8 it has become a lot easier to work with Comparator and Comparable classes in Java. You can implement a Comparator using lambda expression because it is a SAM type interface. It has just one abstract method compare() which means you can pass a lambda expression where a Comparator is expected. Many Java programmers often ask me, what is the best way to learn lambda expression of Java 8?  And, my answer is, of course by using it on your day to the day programming task. Since implementing equals(), hashcode(), compareTo(), and compare() methods are some of the most common tasks of a Java developer, it makes sense to learn how to use the lambda expression to implement Comparable and Comparator in Java.

Difference between List <?> and List<Object> in Java Generics - Example

There is No doubt that Generics is one of the most confusing topics in Java, and you can easily forget concepts and rules, especially if you don't code Java every day. For example, both List<?> and List<Object> looks similar there is a subtle difference between them, the List<?> is basically a list of any type, you can assign a list of String like List<String> or list of Integer i.e. List<Integer> to it. You see the point; it uses the unbounded wildcard <?>, which means any type. It provides it the much needed Polymorphism requires while writing Generic methods. 

Java - Difference between getClass() and instanceof in equals() method?

You might have seen both getClass(), and instanceof operator in Java can be used in the equals() method to verify the type of the object you are checking for equality. Do you know what the difference is between using getClass() vs instanceof operator in Java? What would be the consequence of using one over the other in the equals() method? This is one of the tricky Java interview questions, which some of you might have encountered. There is a very subtle difference between getClass() and instanceof operator, which can cause potential issues with respect to the equals() method. 

How to Read or Parse CSV files with Header in Java using Jackson - Example Tutorial

Hello guys, today I am going to show you how to read a CSV file in Java with a simple example of Jackson API. For a long time, I only knew that Jackson can be used to parse JSON but later realized that you can also use it to parse or read CSV files in Java. The Jackson DataFormat CSV library allows you to read a CSV file in just a couple of lines and it's really powerful and feature-rich. For example, you can read a CSV file with a header or without a header. You can even read a tab-delimited text file like CSV. It's also highly configurable and allows you to define a columns separator to read a text file with any delimiter. You can even use it to directly convert the CSV data into Java objects, just like we do while reading JSON String in Java.

Java 8 StringJoiner Example - How to join multiple Strings with delimiter in Java?

While everyone was looking at the lambda expression and Stream API, JDK quietly sneaked some of the exciting methods on its API. There are a lot of hidden gems on JDK 8 and I have uncovered many of them already in this blog and today we'll talk about one of such gems which you can use in your day-to-day programming activities like joining much String together. The Java 8 has added a new class called StringJoiner to join Strings. The java.util.StringJoiner can be used to join any number of arbitrary String, a list of String, or an array of String in Java. You can choose any delimiter to join String like comma, pipe, colon, or semi-colon. This class also allows you to specify a prefix and suffix while joining two or more String in Java.

Can You Run Java Program Without a Main Method? [Interview Question Answer]

Hello guys, the first thing Java programmers learn is that they need a main method to run, but when they go to any Interview or college viva and ask can run a Java program without a main method, they are surprised like hell. Well, there are actually different types of execution models available in Java; for example, Applets, which run on the browser don't have the main method. Instead, they have life-cycle methods like init(), start() and stop(), which controls their execution. Since Applet is a Java program, you can answer this question is Yes. Similarly, we have Servlet, which runs in a Servlet container, comes as bundled in a web server like Tomcat, or Jetty.

How to Remove an Element from Array in Java with Example

There is no direct way to remove elements from an Array in Java. Though Array in Java objects, it doesn't provide any methods to add(), remove(), or search an element in Array. This is the reason Collection classes like ArrayList and HashSet are very popular. Thanks to Apache Commons Utils, You can use their ArrayUtils class to remove an element from the array more easily than by doing it yourself. One thing to remember is that Arrays are fixed size in Java, once you create an array you can not change their size, which means removing or deleting an item doesn't reduce the size of the array. This is, in fact, the main difference between Array and ArrayList in Java.

How to remove duplicates from Collections or Stream in Java? Stream distinct() Example

Hello guys, if you wonder how to remove duplicates from Stream in Java, don't worry. You can use the Stream.distinct() method to remove duplicates from a Stream in Java 8 and beyond. The distinct() method behaves like a distinct clause of SQL, which eliminates duplicate rows from the result set. The distinct() is also a standard method, which means it will return a new Stream without duplicates, which can be used for further processing. Like other methods of Stream class, I mean, map(), flatmap(), or filter(), distinct() is also lazy, and it will not remove duplicate elements until you call a terminal method on Streams like collect or forEach.  

How to Reverse String in Java with or without StringBuffer Example

Reverse String in Java

There are many ways to reverse a given String in Java. For example, you can use rich Java API to quickly reverse the contents of any String object. Java library provides StringBuffer and StringBuilder class with the reverse() method which can be used to reverse String in Java. Since converting between String and StringBuffer or StringBuilder is very easy it's the easiest way available to reverse String in Java. But, in a coding interview, you may not be allowed to use the JDK API methods to solve this problem. That's why, writing a Java program to reverse String in Java without StringBuffer is one of the popular Java String interview questions, which requires you to reverse String by applying logic and by not using API methods.

What is double colon (::) operator in Java 8 - Example

Hello guys, if you are new to the Java 8 style of coding and wondering what is those double colon(::) in the code then you have come to the right place. In this article, I will explain to you the double colon operator and what it does in Java 8. The double colon (::) operator is known as the method reference in Java 8. Method references are expressions that have the same treatment as a lambda expression, but instead of providing a lambda body, they refer to an existing method by name. This can make your code more readable and concise.

How to copy Array in Java? Arrays copyOf and copyOfRange Example

There are multiple ways to copy elements from one array in Java, like you can manually copy elements by using a loop, create a clone of the array, use Arrays.copyOf() method or System.arrayCopy() to start copying elements from one array to another in Java. Even though both allow you to copy elements from source to destination array, the Arrays.copyOf() is much easier to use as it takes the just original array and the length of the new array. But, this means you cannot copy subarray using this method because you are not specifying to and from an index, but don't worry there is another method in the java.util.Arrays class to copy elements from one index to other in Java, the Arrays.copyOfRange() method. Both methods are overloaded to copy different types of arrays.

How to Join Multiple Strings in Java 8 - String join() Example

Hello guys, I have been writing about the new features of Java SE 8 for quite some time. Initially, my focus areas on much talked about lambda expressions and streams, but slowly I realized that Java 8 is not just about them, it's much more than that. It has many more new features and API enhancements that will help Java developers in their day-to-day job as much as lambdas and streams. One of such less talked features is the ability to join multiple String objects into one separated with any delimiter. It has added a class called StringJoiner in java.util package which we have seen earlier, but it has also added a new method on String class, the join() method, which finally allows you to join Strings in Java.

How to Find Nth Fibonacci Number in Java [Solved] - Example Tutorial

It's been a long time since I have discussed a coding problem in this blog. So, I am going to start with probably the oldest one of them, how do you find the nth number in a Fibonacci sequence? or how do you find the Fibonacci number in Java? or maybe printing the Fibonacci series. If you are a regular reader of this blog then you might know that I have already discussed both recursive and iterative algorithms for printing the Fibonacci series but never really discussed especially writing a program to return the Nth Fibonacci number in Java. Don't worry the wait is over as in this article, we'll solve this common problem and learn a bit more about problem-solving, recursion, iteration, and some basic algorithm skills.

How to Find Square Root of a Number in Java [Solved] - Example Tutorial

Java program for a square root or a number in Java
How to write a Java program to find the square root of a number is a common Java programming exercise that many institutes use in their Java course along with Java program to print Fibonacci series and How to find Armstrong numbers in Java, which we have seen earlier.  Java program for the square root is also a popular question during college semester exams and various programming tests. 

How to implement Binary Tree PreOrder Traversal in Java without Recursion? [Solved] Example Tutorial

This is my second article on how to implement binary tree pre-order traversal in Java. In the first part, I have shown how to traverse a binary tree with a pre-order traversal algorithm using Recursion, and in this article, you will learn how to implement pre-order traversal without using Recursion. You might be thinking that why do you need to learn the iterative solution if a recursive solution is possible and easy to write? Well, this type of question is mostly asked in Programming Job interviews and Interviewers like to see how comfortable a candidate is with both Recursion as well as using other data structures and iteration.

Java 8 Stream map() function Example with Explanation

The map is a well-known functional programming concept that is incorporated into Java 8. Map is a function defined in java.util.stream.Streams class, which is used to transform each element of the stream by applying a function to each element. Because of this property, you can use a map() in Java 8 to transform a Collection, List, Set, or Map. For example, if you have a list of String and you want to convert all of them into upper case, how will you do this? Prior to Java 8, there is no function to do this. You had to iterate through List using a for loop or foreach loop and transform each element. In Java 8, you get the stream, which allows you to apply many functional programming operators like the map, reduce, and filter.

Top 21 Java HashMap Interview Questions and Answers

The java.util.HashMap is one of the workhorses of JDK. Along with ArrayList, it is one of the most used classes from Java's collection framework. There is hardly a real-world Java project, where I haven't seen the use of HashMap. It is an implementation of hash table data structure, and it's not a surprise that HashMap is so useful, as someone has rightly said, "if you could have just one data structure, make it a hash table". The hash table data structure allows you to search for a value in O(1) time if you have a key. In Java, several implementations of hash table data structures exist like Hashtable, ConcurrentHashMap, LinkedHashMap, etc. but HashMap is your general-purpose map.

Top 15 Java 8 Stream and Functional Programming Interview Questions Answers

The JDK 8 release has changed the way we write Java. With new functional programming idioms and a powerful Stream API, most of the new Java code is written in a functional style. This also means that Stream and Functional programming-related questions are increasing on Java interviews. If you are not familiar with Java 8 changes, then it's difficult to crack a Java interview nowadays. Though it's not stated anywhere, most of the companies, particularly Investment banks like Barclays, Citi, and Goldman Sachs, now expect Java developers to know at least Java 8, which is also good, right? Java 11 is already out, and we are looking forward to Java 12 in a couple of months, it makes sense to know at least Java 8 changes.

Bubble sort in Java - Program to sort an Integer Array [Example]

Bubble sort is one of the classic sorting algorithms,s which is used to explain sorting during various computer and engineering courses. Because of its algorithmic nature and simplicity, it's often used in various Java and C++ programming exercises. You may expect questions like the Write Java program to sort integer arrays using bubble sort during any programming interview. Since algorithmic questions are always tricky questions and not easy to code. Even the simplest of them can lead to confusion, especially if you are not gifted with a natural programming head. I have seen many developers fumble if asked to code on the spot. That's why it's advisable to do algorithmic and logical programming during training and learning programming and OOPS to get this skill of converting logic into code.

How to Reverse an Integer in Java without converting to String? Example and Solution

Hello guys, LeetCode has a problem reversing digits of an integer number without using any library method like the reverse() method of StringBuffer. In LeetCode, you can solve this problem with many different languages like Java, C, C++, C#, Python, Ruby, and even JavaScript. Btw, in the article, you will learn how to solve this problem in Java. Before approaching a solution let's first read the problem statement :

Reverse digits of an integer.

Example 1: x = 123, return 321
Example 2: x = -123, return -321

How to implement linked list data structure in Java using Generics? Example

The linked list is a popular data structure for writing programs and lots of questions from a linked list are asked in various Programming Job interviews. Though Java API or JDK provides a sound implementation of the linked list data structure as java.util.LinkedList, a doubly-linked list, you don't really need to implement a linked list of your own for writing production code, but all these interview questions require you to code a linked list in Java for solving coding problems. If you are not comfortable creating your own a linked list, it would be really difficult to solve questions like reversing a linked list or finding the middle element of a linked list in one pass.

4 Examples to Round Floating-Point Numbers in Java up to 2 Decimal Places

Rounding numbers up to 2 or 3 decimal places id a common requirement for Java programmers. Thankfully, Java API provides a couple of ways to round numbers in Java. You can round any floating-point numbers in Java unto n places By using either Math.round(), BigDecimal, or DecimalFormat. I personally prefer to use BigDecimal to round any number in Java because of it's convenient API and support of multiple Rounding modes. Also, if you are working in the financial industry, it's best to do a monetary calculation in BigDecimal rather than double as I have discussed in my earlier post about common Java mistakes. 

Difference between Abstract class and Interface in Java 8? Answer

Ever since JDK 8 has allowed concrete (non-abstract) methods on the interface like default and static methods, many of my readers have asked me how should they answer the classical abstract class vs interface questions. Earlier, an interface cannot have any concrete methods and that was the main difference between abstract class and interface but now that is not the case. In this post, I'll revisit this hugely popular Java interview question in light of Java 8 changes. This is also a popular Java interview question and knowing the difference will help you to answer this question in a real interview.

How to Attach Apache Tomcat Server in Eclipse for Running and Debugging Java Web Application - Steps

Hello Java programmers, If you are doing Java Web development in Eclipse, then you definitely would like to run and debug your Java application right from Eclipse. To do so, you need to add Apache Tomcat in the Eclipse version you are using, like Eclipse Kepler, Oxygen, Photon, or Luna. Eclipse comes in multiple flavors, like Eclipse IDE for Java Developers, which is suitable for developers doing core Java work, and Eclipse IDE for Java EE developers, which is for people doing enterprise Java work, like developing Servlet, JSP, and EJB based applications in Eclipse. In fact, the Java EE version of Eclipse is also one of the most downloaded software built with Java, so far, more than 1 million programmers have downloaded it.

How to find difference between two dates in Java 8? Example Tutorial

One of the most common programming task while working with date and time objects are calculating the difference between dates and finding a number of days, months, or years between two dates. You can use the Calendar class in Java to get days, months between two dates. The easiest way to calculate the difference between two dates is by calculating milliseconds between them by converting java.util.Date to milliseconds using the getTime() method. The catch is converting those milliseconds into Days, Months and Year is not tricky due to leap years, the different number of days in months, and daylight saving times.

Top 5 Java 8 Default Methods Interview Questions and Answers

Hello guys, If you are preparing for Java interviews and want to learn about default methods in Java then you have come to the right place. In the last couple of articles, I have to talk about default methods introduced in JDK 8. First, we have learned what is the 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 supports multiple inheritances now in JDK 8 (see here) and how Java handles the diamond problem that will arise due to default methods.