How HashSet works in Java [Explained]

Not many Java programmers know that HashSet is internally implemented using HashMap in Java, so if you know How HashMap works internally in Java, more likely you can figure out how HashSet works in Java. But, now a curious Java developer can question that, how come HashSet uses HashMap because you need a key-value pair to use with Map, while in HashSet we only store one object. Good question, isn't it? If you remember some functionality of the earlier class, then you know that HashMap allows duplicate values, and this property is exploited while implementing HashSet in Java.

When to use ArrayList vs LinkedList in Java? [Answered]

When to use ArrayList or LinkedList in Java is one of the most popular Java interview questions and also asked as a difference between ArrayList and LinkedList. Earlier, I have shared common Java collections interview questions and in this article, I will explain the difference between them. ArrayList and LinkedList are two popular concrete implementations of the List interface from Java's popular Collection framework. Being List implementation both ArrayList and LinkedList are ordered, the index-based and allows duplicate. Despite being from the same type of hierarchy there are a lot of differences between these two classes which makes them popular among Java interviewers.

Top 10 Free and Best Online Courses to Learn Data Structure and Algorithms in Java in 2021 - Best of Lot

Hello guys, In the past, I have shared a lot of useful resources like books and tutorials to learn Data Structure and Algorithms for both beginners and experienced programmers. I have also shared a lot of Data Structure and Algorithmic interview questions like this and their solutions in Java. Still, I have got continuously queries about excellent online courses to learn Data Structure and Algorithms in Java. Even though the topics are completely independent with the programming language, Java developer definitely likes the online courses which teach Data Structure and Algorithms in Java, and that's why my recent post about best algorithms courses, which includes algorithms courses from JavaScript and Python didn't impress my readers.

How to Convert Stream to ArrayList in Java 8 - Collectors.toCollection() Example

You can use Collectors.toList(), toSet(), and toMap() to get all elements of Stream into any Collection like List, Set or Map, but if you want to get a particular collection e.g. ArrayList, then you need to use Collectors.toCollection(ArrayList::new) method. This method first creates an ArrayList using method reference and then adds all elements of Stream into the ArrayList. It's very useful if you have a long list of String and you want to create a smaller list containing only String starting with the letter "b"  like "Bluehost"

Top 10 Free Java Courses in 2021 for Beginners and Experienced Programmers - Best of Lot

Hello guys, the Internet is full of useful resources, and no matter what you want to learn, there is something useful available for free. You just need to commit your time and effort. But at the same time, it's challenging to choose from the massive sea of free tutorials and courses on the internet. If you are not careful, you will spend most of your time browsing and changing classes without learning anything. That's where a curated list helps. Curation is my hobby and passion. I love to read books and courses which allows me to curate useful resources and share them with you guys.

Caused by: java.sql.SQLSyntaxErrorException: ORA-01722: invalid number - Solution

Hello guys, if you are getting below error in your Java program and wondering how to solve this or just stuck then you have come to the right place. In this article, I will explain to you what causes the " java.sql.SQLSyntaxErrorException: ORA-01722: invalid number" error when you connect to an Oracle database from a Java program and how you can solve it. 

But, first of all, let's take a look at the stack trace of this error which looks like below:
Caused by: java.sql.SQLSyntaxErrorException: ORA-01722: invalid number  at oracle.jdbc.driver.T4CTTIoer.processError(
        at oracle.jdbc.driver.T4CTTIoer.processError(
        at oracle.jdbc.driver.T4C8Oall.processError(
        at oracle.jdbc.driver.T4CTTIfun.receive(
        at oracle.jdbc.driver.T4CTTIfun.doRPC(
        at oracle.jdbc.driver.T4C8Oall.doOALL(
        at oracle.jdbc.driver.T4CPreparedStatement.doOall8(
        at oracle.jdbc.driver.T4CPreparedStatement.executeForDescribe(
        at oracle.jdbc.driver.OracleStatement.executeMaybeDescribe(
        at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(
        at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(
        at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(
        at oracle.jdbc.driver.OraclePreparedStatementWrapper.executeQuery(

Top 10 Java 9 and Module Tutorials and Courses in 2021 - Best of Lot

It's been more than a couple of years or so since JDK 9 was launched, and the new year is probably the best time to learn Java 9 and get yourself familiar with new features and enhancements on existing APIs. The highlight of the JDK 9 release was Project Jigsaw or Module system. The Java 9 Platform Module System allows Java to move forward by modularizing the JDK as well as adding modules as first-class citizens to Java, but that's not the only thing to look forward to, there are many small changes that are very useful in day-to-day coding.

Java 8 Optional isPresent(), OrElse() and get() Examples

The Optional class in Java is one of many goodies we have got from the Java 8 release. If you use it correctly, Optional can result in clean code and can also help you to avoid NullPointerException which has bothered Java developers from its inception. Even though many of us have used null to indicate the absence of something, the big problem is that if you call a method or access a field on the null object (except static fields), you will get a NullPointerException and your whole program may crash. 

Top 5 Free Big Data Courses in 2021 for Java Programmers to Learn Hadoop, Spark - Best of Lot

Hello Java Programmers, If you want to learn Big Data technologies in 2021 like Hadoop, Apache Spark, and Apache Kafka and you are looking for some free resources like books, courses, and tutorials, then you have come to the right place. In this article, I am going to share some of the best free online courses to learn Hadoop and Spark from Udemy and Pluralsight at your own pace. I personally like to start with FREE resources before I have enough knowledge to choose the right book or enroll in a little expensive course. It's also my passion to surf the web to find great free resources and share them with you guys.

3 Examples to Loop over a List in Java - ArrayList, LinkedList or Vector

3 ways to Loop through a List in Java
There are multiple ways to traverse or loop through a List in Java e.g. by using an Iterator, by using an enhanced for loop of Java 5, and not the forEach() method of Java 8. Given a List is an index-based collection if you know the index you can retrieve an object from a List and because of this, you can also use a traditional for loop which keeps count for iterating a List. Now the question is whether should you use the Iterator or enhanced for loop, or the forEach() method of Java 8 for looping over List in Java. 

Top 5 Free Courses to Learn C# (C-Sharp) in 2021 - Best of Lot

Many people underestimate the power of C# and never think highly of it when they talk about programming languages. Still, the truth is that C# is one of the popular programming languages of today's world, just behind JavaScript, SQL, and Java on StackOverFlow's Developer Survey for the last couple of years. There are a lot of jobs and opportunities available for experienced C# developers. It's one of the critical languages for developers working with Microsoft technologies like Windows and SQL Server. It is also one of the most popular programming languages for developing desktop GUI, surpassing Java Swing entirely in the last couple of years. I have seen many big investment banks switched from Swing to C# for their GUI development work.

Java 8 - Map and Reduce Example

Hello folks, the map-reduce concept is one of the powerful concepts in computer programming, particularly on functional programming which utilizes the power of distributed and parallel processing to solve a big and heavy problem in a quick time. From Java 8 onwards, Java also got this powerful feature from the functional programming world. Many of the services provided on the internet like Google Search are based on the concept of the map and reduce. In map-reduce, a job is usually split from the input data-set into independent chunks which are processed by the map tasks in a completely parallel manner. The framework then sorts the outputs of the map operation, which are then supplied to the reduce tasks.

6 Free Blockchain Online Courses and Certifications for Beginners in 2021 - Best of Lot

Hello guys, if you want to learn Blockchain development and looking for some free Blockchain courses then you have come to the right place. Earlier, I have shared my favorite and best blockchain courses for programmers and a lot of you asked for free online courses to learn Blockchain so today, I am going to share the best free Blockchain development courses you can join in 2021. Blockchain is one of the most in-demand technologies and one skill that you should learn in 2021. It will not only help in your career but also raise your profile. This is one thing I have highly recommend programmers to learn this year. 

4 Examples to Convert an int to String in Java [UPDATED]

Hello guys, if you new to Java programming and wondering how to convert an int to a String object in Java then don't worry, you have come to the right place. Earlier, I have shown you how to convert an Integer to a String and in this article, I will show you how to convert an int variable to a String in Java. The difference between an Integer and an int is that the former is an object while an int variable is a primitive value. You can use the String.valueOf() or Integer.toString() method to convert an int value to a String object in Java. Remember, String is not just a char array but a full feature object in Java. 

Top 5 Free Android Development Courses for Beginners in 2021 - Best of Lot

Hello guys, If you are passionate about creating mobile games and applications and want to learn how to develop Android apps or want to become an Android application developer, then you have come to the right place. In this course, I am going to share some of the best and free Android development courses for Java programmers and others. You might know that earlier Java was the only language that is used to create Android applications. Still, since last year, Google has announced Kotlin as the official language for Android app development, which means you can use either Kotlin or Java to create Android apps.

3 ways to Convert Integer to String in Java [Example]

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

How to Queue Interface in Java? Example Tutorial

The JDK provides an implementation of several data structures in the Java collection framework like ArrayList is a dynamic array, LinkedList represents a linked list, HashMap represents a hash table data structure, and Queue interface represent queue data structure. Btw, If you are not familiar with data structure itself, then you can also see Introduction to Data Structures & Algorithms in Java, an excellent course to start with the essential data structure in Java. The Queue data structure allows you to process elements in the first in first out order, and that's why it is also known as a FIFO data structure. 

How to Convert Date to LocalDate in Java 8 - Example Tutorial

Hello guys, if you want to learn how to convert old Date to new LocalDate in Java 8 then you have come to the right place. Earlier, I have shared 10 examples of LocalDate in Java 8, and in this article, I am going to teach you how to convert Date to LocalDate in Java. you may know that JDK 8 introduced the new Date and Time API, which has got a new set of shiny date classes like LocalDate, LocalTime, etc, but you still have a lot of code written against java.util.Date? In order to work with that code, you should know how to convert java.util.Date to java.util.LocalDate in Java.