Hello guys, you might have heard about it, Can you tell me any design pattern which you have used recently in your project, except Singleton? This is one of the popular questions from various Java interviews in recent years. I think this actually motivated many Java programmers to explore more design patterns and actually look at the original 23 patterns introduced by GOF. The Strategy design pattern is one of the useful patterns you can mention while answering such a question. It's very popular, and there are lots of real-world scenarios where the Strategy pattern is very handy.
10 Examples Of du Command in Linux
Here, we shall be looking at another command in Linux. The” du” command. Before giving the examples you can use with it I will be explaining the du itself, What is being used for and When to use it, and How to use it
So Firstly, What is DU or What does the command mean?
The full meaning of du is Disk usage. This helps in planning and maintaining the file’s space. The command is used to keep track of any files or directories that are taking up too many spaces in the hard disk drive. Now we shall be taking the examples one after the other.
3 Examples of for loop in Linux and Bash Script [Tutorial]
Hello guys, if you want to learn how to use for loop in bash or Linux then you have come to the right place. Earlier, I have shared free Linux courses and free bash scripting courses, and today, I am going to share three simple examples of using for loop in Linux. If you are a Programmer, Software Engineer, or System Administrator working in a UNIX or Linux environment, then you will probably find the shell 'for' loop to be a handy tool for automating simple command-line tasks. This is the single command which has helped me a lot while doing production support and performing operational tasks.
10 ways to Quit/Exit from Vim Editor in Linux/UNIX? Examples
Hello guys, if you are stuck inside VIM editor and looking for a way to come out then you have come to the right place. In the past, I have shared the free Linux courses and today, I am going to talk about Vim or VI editor, one of the most important tools for people working in Linux. You might not know but many developers struggle to get out of commands like Vim and telnet. I can say that because there was a time when I spend a good amount of time coming out from the telnet window.
10 Example of ps -ef command in Linux and UNIX
Hello guys, It's been a long time since I wrote about the Linux command in this blog. In my last article, I have shared free Linux courses for beginners which many of you guys have liked, that's why I am writing another post on Linux, this time about the "ps" command. If you have worked on a Linux machine then you are likely to be familiar with the "ps" command. The "ps" command is used to check the process status. It stands for "process statistics" and you can use the ps command to see all the processes and find things like PID which can be used to interact with the process. For example, you can kill a process by passing PID to kill command in Linux as shown here.
10 Examples of df Command in Linux
Hello, In Today’s article we shall be talking about the df command in Linux. The objectives of this article are: What is the df command, and what does it mean? How is it used? I shall be providing 10 different examples or scenarios for it and when to use it
What does df mean?
The meaning of df in Linux is disk-free or disk file system. Which is used to display the file system in the likes of total storage space, available storage space and etc.
Df command in Linux is a command or syntax in Linux that you doing away with it is almost impossible
You may begin to wonder or ask Why or When do You need to use it?
How to use PreparedStatement in Java - JDBC Example Tutorial
PreparedStatement is used to execute specific queries that are supposed to run repeatedly, for example, SELECT * from Employees WHERE EMP_ID=?. This query can be run multiple times to fetch details of different employees. If you use PreparedStatement like above then the database assists in query preparation, which is faster and more secure. Such kinds of queries are compiled, and their query plans are cached at the database side every time you execute it, you will get a faster response as opposed to using simple queries via Statement object, like SELECT * from Employees WHERE EMP_ID + emp_id.
How to Create and Start Multiple Threads in Java? - Example Tutorial
Hello guys, Multithreading is one of the biggest strengths of Java, which allows you to divide a task and execute faster by using more than one thread. In order to use multiple threads in Java, you need to first define the task which will be executed by those threads. In order to create those tasks, you can either use the Runnable or Callable interface. If you are just learning Java chose the Runnable interface, it's a simpler one, but if you are familiar with Java multithreading and want to leverage additional features offered by Callable like it can throw an exception and it can also return value, then go ahead and use the Callable interface. Once you have the task ready, you need to create an instance of the Thread class.
How to use wait, notify, and notifyAll in Java? Example Tutorial
When should you use the wait() and notify method in Java is one of the many popular questions about the wait and notify methods from Java multithreading interview questions. One of the reasons for its popularity is that still a lot of Java programmers struggle to explain and write code using wait-notify methods. Many Java developer only knows some facts about the wait and notify methods like that wait() and notify() are defined in the java.lang.Object class or you cannot call wait() without synchronization, which means without a synchronized block or synchronized method but doesn't really know when and how to use them.
How to Join and Merge Two ArrayLists in Java - Example Tutorial
You can use the addAll() method from java.util.Collection interface to join two ArrayLists in Java. Since ArrayList implements List interface which actually extends the Collection interface, this method is available to all List implementations including ArrayList e.g. Vector, LinkedList. The Collection.addAll(Collection src) method takes a collection and adds all elements from it to the collection which calls this method like target.addAll(source). After this call, the target will have all elements from both source and target ArrayList, which is like joining two ArrayList in Java.
What is Iterator in Java? Example
Hello guys, if you are wondering what is Iterator in Java and how does it
work? when you are supposed to use Iterator and what advantages or
disadvantages it provide over other methods of iterating over Java Collections
then you have come to the right place. In the past, I have shared
how HashMap works in Java
and
How Garbage collection works
and in this article, I am going to share how Iterator works and how they
simplify iteration irrespective of different collection types. You all may
know about Java collections. It has many lists, maps, etc in it. Now, you may
know how to use the inbuilt LinkedList or any other collection, but once that
collection is built, how will you iterate over it? I know you all are thinking
of loops.
How to convert Java object to JSON String using Gson? Example Tutorial
If you are a Java or Android developer and learning JSON to support JSON format for your project and looking for a quick and simple way to convert your Java object into json format then you have come to the right place. In this article, I'll teach you how to convert a Java object to a JSON document using Google's Java library called Gson. This library allows you to convert both Java objects to JSON String and a JSON document to Java objects. So, let's first do some serialization. Serialization in the context of Gson means mapping a Java object to its JSON representation.
Why String is Immutable or final in Java - 5 Reasons
There is hardly any Java Interview, where no questions are asked from String, and Why String is Immutable in Java is I think most popular Java String question. This question is also asked as Why String class is made final in Java or simply, Why String is final. In order to answer these questions, Java programmer must have a solid understanding of how String works, what are special features of this class, internal structure and implementation of String and some key fundamentals. The String class is a God class in Java, It has got special features which is not available to other classes like String literals are stored in string pool.
Difference between Array vs ArrayList in Java
What is the difference between Array and ArrayList is quite a common question among beginners especially those who started coding in C and C++ and prefer to use Array? Both Array and Array List are used to store elements, which can be either primitive or objects in case of Array and only objects in case of ArrayList in Java. The main difference between Array vs ArrayList in Java is the static nature of the Array and the dynamic nature of ArrayList. Once created you can not change the size of Array but ArrayList can re-size itself when needed.
Difference between HashMap and ConcurrentHashMap in Java? Example
HashMap vs ConcurrentHashMap in Java
What is the difference between an HashMap and ConcurrentHashMap in Java is one of the common interview questions and knowing the answer is not just important for interviews but also for writing robust and high performance Java cocd. ConcurrentHashMap in Java is introduced as an alternative of Hashtable in Java, which is a synchronized collection class, that makes the main difference between HashMap and ConcurrentHashMap which is one is non-synchronized , non-thread safe and not for use in Concurrent multi-threaded environment while ConcurrentHashMap is a thread-safe collection and intended to be used as primary Map implementation especially for multi-threaded and Concurrent environment.
What is the difference between an HashMap and ConcurrentHashMap in Java is one of the common interview questions and knowing the answer is not just important for interviews but also for writing robust and high performance Java cocd. ConcurrentHashMap in Java is introduced as an alternative of Hashtable in Java, which is a synchronized collection class, that makes the main difference between HashMap and ConcurrentHashMap which is one is non-synchronized , non-thread safe and not for use in Concurrent multi-threaded environment while ConcurrentHashMap is a thread-safe collection and intended to be used as primary Map implementation especially for multi-threaded and Concurrent environment.
How to iterate over an Array in Java using foreach loop Example Tutorial
Though there are many ways to loop over Array in Java, including classical for loop, while loop with length counter, nothing matches the elegance of Java 1.5 foreach loop, which makes iteration super easy and super cool. When we need to iterate through each element of an array and have to perform some operation on them e.g. filtering, transformation, or simply printing, the foreach loop comes to its full glory. There is not much difference between traditional for loop and Java 1.5 foreach loop, except that the former has counter and condition, which is checked after each iteration.
Difference between List and Set in Java [Answered]
List vs Set in Java
The main difference between List and Set is that List is an ordered Collection while Set is an unordered collection. Java collection framework offers several collection classes for various needs but all collections can be divided into broadly three categories: List, Set, and Map. All List, Set, and Map are defined as interfaces and then you have several implementations like ArrayList and Vector are the popular implementation of List interface, while HashSet is a popular implementation of the Set interface.
2 Ways to Remove Elements/Objects From ArrayList in Java [Example]
There are two ways to remove objects from ArrayList in Java, first, by using the remove() method, and second by using Iterator. ArrayList provides overloaded remove() method, one accepts the index of the object to be removed i.e. remove(int index), and the other accept objects to be removed, i.e. remove(Object obj). The rule of thumb is, If you know the index of the object, then use the first method which accept index, otherwise use the second method. By the way, you must remember to use ArrayList remove methods, only when you are not iterating over ArrayList if you are iterating then use Iterator.remove() method, failing to do so may result in ConcurrentModificationException in Java.
How to check if File is Empty in Java? Example Tutorial
One of the readers of my blog Javarevisited emailed me yesterday about how to check if a file is empty in Java and that's why I am writing this post to show that using an example. The common approach for checking if a file is empty or not is to first check if the file exists or not and then check if it contains any content, but Java has done that hard work for you. Well, it's pretty easy to check emptiness for a file in Java by using the length() method of the java.io.File class. This method returns zero if the file is empty, but the good thing is it also returns zero if the file doesn't exist. This means you don't need to check if the file exists or not.
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".
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