How to read and write Images in java using ImageIO Utility

Writing an Image file in Java is very common scenario and in this article we will see a new way to write images into file in Java. javax.imageio.ImageIO is a utility class which provides lots of utility method related to images processing in Java. Most common of them is reading form image file and writing images to file in java. You can write any of .jpg, .png, .bmp or .gif images to file in Java. Just like writing, reading is also seamless with ImageIO and you can read BufferedImage directly from URL.

Inversion of Control and Dependency Injection design pattern with real world Example - Spring tutorial

Inversion of Control and Dependency Injection is a core design pattern of Spring framework. IOC and DI design pattern is also a popular design pattern interview question in Java. As the name suggest Inversion of control pattern Inverts responsibility of managing the life cycle of the object e.g. creating an object, setting their dependency etc from application to a framework, which makes writing Java application even more easy. The programmer often confused between IOC and DI, well both words used interchangeably in Java world but Inversion of Control is a more general concept and Dependency Injection is a concrete design pattern.

How to split a comma separated String in Java? Regular Expression Example

You can use the String.split() function or StringTokenizer class to split a comma-separated String in Java. Since splitting a String is a very common functionality, Java designers have provided a couple of split() method on java.lang.String class itself. These split() function takes a regular expression and split the String accordingly. In order to parse a comma-delimited String, you can just provide a "," as a delimiter and it will return an array of String containing individual values. The split() function internally uses Java's regular expression API (java.util.regex) to do its job.

2nd highest salary in Oracle using ROW_NUMBER and RANK in Oracle and MSSQL

This is the second article about calculating the 2nd highest salary in SQL. In the first part, you have learned how to find the second highest salary in MySQL, SQL SERVER and by using ANSI SQL, which should also work in all database which confirms ANSI standard e.g. PostgreSQL, SQLLite, etc. In this part, I will show you how to find the 2nd maximum salary in Oracle and SQL SERVER using ROW_NUMBER(), RANK(), and DENSE_RANK() method. These are window function in Oracle, which can be used to assign unique row id, or rank to each row based on any column and then select the right row.

Scala vs Java - Differences and Similarities

Scala is new generation JVM language, which is generating popularity as an alternative of arguably one of the most popular language Java. It's not yet as popular as Java, but slowly getting momentum. As more and more Java developers are learning Scala and inspired by Twitter, more and more companies are using Scala, it's future looks very bright. To start with, Scala has several good feature, which differentiate it from Java, but same time it has lot of similarities as well e.g. both Scala and Java are JVM based language, You can code Scala in Java way and Scala can use any Java library, which in my opinion a great decision made by designers of Scala.

5 Free OCAJP8, OCPJP8 Mock Exams and Practice questions - 1Z0-808 809 (Java 8 Certification)

In order to do well on Java certifications, you need good books and a reasonable number of practice questions before you go for exams. Practice questions and mock exams will help you to assess your topic-wise preparation level and help you to identify your strong and weak areas. Based on the result of the mock exams, you can concentrate on areas where you lack expertise e.g. multi-threading is one of the tricky areas. It will also expose you to exam patterns and different types of questions you can expect in examination e.g. multiple choice questions, rearranging code, fill in the blanks etc. Though I highly recommend commercial exam simulators like Whizlabs and Enthuware, I also suggest you take advantage of many mock questions which are freely available.

How to replace NULL with Empty String in SQL Server? ISNULL() vs COALESCE() Examples

We often need to replace NULL values with empty String or blank in SQL e.g. while concatenating String. In SQL Server, when you concatenate a NULL String with another non-null String the result is NULL, which means you lose the information you already have. To prevent this, you can replace NULL with empty String while concatenating. There are two ways to replace NULL with blank values in SQL Server, function ISNULL(), and COALESCE(). Both functions replace the value you provide when the argument is NULL like ISNULL(column, '') will return empty String if the column value is NULL.

How to Use Locks in Multi-threaded Java Program

Many Java programmers confused themselves like hell while writing multi-threaded Java programs like where to synchronized? Which Lock to use? What Lock to use etc. I often receive a request to explain how to use Locks in Java, so I thought to write a simple Java program, which is multi-threaded and uses a rather new Lock interface. Remember Lock is your tool to guard shared resources which can be anything e.g. database, File system, a Prime number Generator, or a Message processor. Before using Locks in Java program, it’s also better to learn some basics. Lock is an interface from java.util.concurrent package. It was introduced in JDK 1.5 release as an alternative of the synchronized keyword.

Effective Java, 3rd Edition - Covers JDK 7, 8, and 9 - Must Read Book for Java Programmers

Hello guys, I have an interesting news to share with you today. After a long wait of almost 10 years, the Effective Java 3rd edition is finally coming this year, hopefully, December 2017. The Effective Java 2nd Edition was released in May 2008 and updated for Java SE 6, but it been, good 10 years now and there is a lot of interest from Java developers around the world for Effective Java 3rd edition after Java SE 8 release and I am very happy to inform you guys that, finally, all our wishes are granted and Effective Java 3rd edition is set to arrive this year. It will not only cover Java 9 release but also all the changes from Java 7 and Java 8.

SQL Server JDBC Error: The TCP/IP connection to the host Failed

I had installed SQL SERVER 2014 Express edition and I was trying to connect to SQL SERVER from Java program using JDBC, but I was repeatedly getting the following error:

com.microsoft.sqlserver.jdbc.SQLServerException: The TCP/IP connection to the host localhost, port 1433 has failed. Error: "connect timed out. Verify the connection properties. Make sure that an instance of SQL Server is running on the host and accepting TCP/IP connections at the port. Make sure that TCP connections to the port are not blocked by a firewall.".Error while closing connection !!null

Right way to Close InputStream and OutputStream in Java

For some unknown reasons many Java programmers are not very comfortable with IO package. I don't know why, but I have found them much more comfortable with java.lang and java.util than java.io. One possible reason of this could be that, writing IO code require a bit of C++ like programming, which involves doing clean-up, releasing resources once done etc. Since Java made coding a lot easier by taking care of memory management, unknowingly it also introduced bad practice of not releasing resource after use e.g. database connections, socket connection, files, directory, printers, scanners or any other scarce resource.

20 Questions You can ask to Interviewer in Programming Job Interviews?

From the first round to HR round, from telephonic to face-to-face, in almost all kind of programming interviews, there will be a time when Interviewer will give you a chance to ask questions. Many programmers are too concern about asking questions, and they politely decline ; Well it's your chance to learn about the Job you are going to do, and you shouldn't let this opportunity goes away. The interviewer, also judges you by your questions; a good, thoughtful, positive question can create the great impression on Interviewer's mind. It also shows that  the interest of a candidate for a Job.

How to remove all elements from ArrayList in Java - Clear vs RemoveAll

Many times we want to reset an ArrayList for the reusing purpose, by resetting we mean clearing it or removing all elements. There are two ways to reset an ArrayList in Java, by using clear() method or calling removeAll(). If your ArrayList is small enough e.g. contains only 10 or 100 elements then you can use any of these two methods without worrying too much, but, if you have a huge list of lots of objects e.g. an ArrayList containing 10M entries, then choice of clear() vs removeAll() can make a huge difference in performance of your Java application. Sometimes it's even better to create a new ArrayList instead of resetting the old one, especially if resetting takes a long time, but this also has a caveat, you need to make sure that old ArrayList is eligible for garbage collection, otherwise there is a huge risk of java.lang.OutOfMemoryError: Java Heap Space.

Java 8 forEach() Loop Example

Java 8 has introduced a new way to loop over a List or Collection, by using the forEach() method of the new Stream class. You can iterate over any Collection e.g. List, Set, or Map by converting them into a java.util.sttream.Stream instance and then calling the forEach() method. This method performs given operation on every element of Stream, which can be either simply printing it or doing something else. Since stream can be sequential or parallel, the behavior of if this method is not deterministic if used with a parallel stream. One more thing to remember about the forEach() method is that it's a terminal operation, which means you cannot reuse the Stream after calling this method. It will throw IllegalStateException if you try to call another method on this Stream.

How to read File into String in Java 7, 8 with Example

Many times you want to read contents of a file into String, but, unfortunately, it was not a trivial job in Java, at least not until JDK 1.7. In Java 8, you can read a file into String in just one line of code. Prior to the release of new File IO API, you have to write a lot of boilerplate code e.g. open an input stream, convert that input stream into a Reader, and then wrap that into a BufferedReader and so on. Of course, JDK 1.5's Scanner class did provide some breathing space but it was still not as simple as it should be, like in Python or Ruby. By using Java 7 new File API and Java 8's new features like lambda expression and stream API, Java is now close to Python or other utility languages, when it comes to reading the file into String.

Eclipse - java.lang.ClassNotFoundException: org.springframework.web.servlet.DispatcherServlet in Tomcat

Problem : You are getting java.lang.ClassNotFoundException exception complaining that Spring's DispatcherServlet class is not available in the classpath. This error is coming while running a Spring MVC based Java application from Eclipse and Tomcat as Server (running inside Eclipse IDE itself). You have either included spring framework JAR files manually by yourself or you are using Maven to download and manage dependent JAR files. Here is the stack trace of this error :

java.lang.ClassNotFoundException: org.springframework.web.servlet.DispatcherServlet
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1678)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1523)
    at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:525)
    at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:507)
    at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:126)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1099)
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1043)
    at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4957

3 Examples of Parsing HTML File in Java using Jsoup

HTML is the core of the web, all the pages you see on the internet are HTML, whether they are dynamically generated by JavaScript, JSP, PHP, ASP or any other web technology. Your browser actually parse HTML and render it for you. But what would you do,  if you need to parse an HTML document and find some elements,  tags, attributes or check if a particular element exists or not from Java program. If you have been in Java programming for some years, I am sure you have done some XML parsing work using parsers like DOM and SAX, but there is also good chance that you have not done any HTML parsing work. Ironically, there are few instances when you need to parse HTML documents from core Java application, which doesn't include Servlet and other Java web technologies.

Maven JAR Artifiact Dependency Search Not Working in Eclipse - Solved

Recently I face a strange issue while using Maven in Eclipse via M2Eclipse plugin. I have created a Maven Java project in Eclipse and subsequently tried to add Spring framework as a dependency, to my surprise, nothing was happening. Eclipse was not able to search dependency in Maven central repository. I was surprised because I have never faced this issue while I was using the M2Eclipse plugin for a long time. After some trial and error, I realized that this is my brand new workspace and I am running with Eclipse Luna, the newest version of Eclipse which I had just downloaded a couple days of the back. My first hunch was that Eclipse might not able to connect to the Internet, and to verify that I tried connecting the Eclipse market place, and boom it was working fine.

Difference between SOAP and RESTful Web Service in Java

Though both SOAP and RESTful web services allow a client to query the server for some information, the way they are implemented and used is quite different. The main difference between SOAP and REST is that former provides a standard of communication between client, server and other parties and has restricted a set of rules and format, while REST leverages the ubiquity of HTTP protocol, in both client and servers, to allow them to communicate with each other regardless of their implementation. In short, getting data from a RESTful web service requires less headache than getting data from a SOAP web service.

Quicksort Sorting Algorithm in Java - Example and Explanation

Quicksort algorithm is one of the most used sorting algorithms, especially to sort the large lists, and most of the programming languages, libraries have implemented it in one or another way. In Java, Arrays.sort() method sorts primitive data types using a double-pivot Quicksort algorithm, authored by Joshua Bloch and others. This implementation provides better performance for a lot of data sets, where traditional quicksort algorithms reduced into quadratic performance. This method also uses MergeSort, another good sorting algorithm, to sort objects. QuickSort implementations are also available in the C++ STL library.

How to calculate Large Factorials using BigInteger in Java?

Factorial of numbers greater than or equal to 13 cannot be found using primitive int data type as shown in our earlier factorial solution due to overflow. These factorials are too large to fit in an int variable, whose maximum value is just 2147483647 (2^31 -1). Even if we use the long data type, factorials greater than or equal to 21 will generate an overflow. To find the factorial of anything above 21, you need to use the BigInteger class from the java.math package. As the name suggests, BigInteger class is designed to hold really large integer value, something which is even bigger than the maximum value of long primitive e.g. 2^63 -1 or 9223372036854775807L. You also need to change the way we calculate factorial for a smaller number. You can not use recursion to calculate factorial of a larger number instead we need to use for loop for that.

How to format/parse dates with LocalDateTime in Java 8 - Example Tutorial

One of the common tasks in Java project is formatting or parsing date to String and vice-versa. Parsing date means you have a String which represents a date e.g. "2017-08-3" and you want to convert it into an object which represents the date in Java e.g. java.util.Date in pre-Java 8 world and LocalDate or LocalDatetime in Java 8 world. Similarly, formatting a date means converting a date instance into String, for example, you have a Date object or LocalDatetime object and you want a String in dd-MM-yyyy format. Java 8 API provides good support for formatting and parsing dates.

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 file, 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 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 icons directory of your project, how do you load them? The answer is by using java.lang.Class' getResource() and getResourceAsStream() method. These method accepts the path of resource as String and returns URL and InputStream respectively.

How to sort a Map by keys in Java 8 - Example Tutorial

In the last article, I have shown you how to sort a Map by values in Java 8, and in this tutorial, you will learn how to sort a Map by keys lik a HashMap, ConcurrentHashMap, LinkedHashmap, or even Hashtable. Theoretically, you cannot sort a Map because it doesn't provide any ordering guarantee. For example, when you iterate over a HashMap, you don't know in which order entries will be traversed because HashMap doesn't provide any ordering. Then, how can you sort a Map which doesn't support order? Well, you can't and that's why you only sort entries of HashMap but you don't store the result back into HasMap or any other Map which doesn't support ordering. If you do so, then sorting will be lost.

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 keyword. Methods with default keyword 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 e.g. 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 forEach() method, they face a daunting challenge of breaking all implementation of 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 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 real world date and time nuisance like leap seconds, leap years, and daylight saving time.

3 Ways to Read File line by line in Java 8? Examples

Java 8 has added a new method called lines() in Files class which can be used to read a file line by line in Java. The beauty of this method is that it reads all lines from a file as Stream of String, which is populated lazily as the stream is consumed. So, if you have a huge file and you only read the first 100 lines then the rest of the lines will not be loaded into memory, which results in better performance. This is slightly different from than Files.readAllLines() method (which reads all lines into a List) because this method reads the file lazily, only when a terminal operation is called on Stream e.g. forEach(), count(), etc. By using count() method you can actually count a number of lines in files or number of empty lines by filtering empty lines.

How to Create Thread Pool in Java using Executor Framework - Example Tutorial

Java 1.5 introduced a Thread pool in Java in the form of an Executor framework, which allows Java programmers to decouple submission of a task to the execution of the task. If you are doing server-side programming in Java than the Thread pool is an important concept to maintain scalability, robustness, and stability of the system. For those, who are not familiar with thread pool in Java or concept of thread pool here is a one-liner, Thread pool in Java is a pool of worker threads, which is ready to perform any task given to them, mostly in the form of implementation of Runnable or Callable interface.

Top 50 Java Programs from Coding Interviews

Coding is an integral part of any programming job interviews, and Java development interviews are no exception. I would even suggest you should never hire anyone without testing their coding skill, coding is also an art, and more often than a good code is an excellent developer as well. If you look at tech giants like Amazon, Facebook, and Google they thoroughly test the coding skill of any developer they hire, notably Amazon who first send online coding exercises to filter Java programmers who can code. This online test usually gives you requirements and ask you to write a program in a limited time, usually 2 to 3 hours. The application should meet the output provided by the exercise itself. These type of tasks are very tough to crack if you don't have excellent coding skill.

Difference between get and load in Hibernate

get vs load in Hibernate
Difference between get and load method in Hibernate is one of the most popular questions asked in Hibernate and spring interviews. Hibernate Session class provides two methods to access object e.g. session.get() and session.load() both looked quite similar to each other but there are subtle differences between load and get method which can affect the performance of the application. The main difference between get() vs load method is that get() involves database hit if an object doesn't exist in Session Cache and returns a fully initialized object which may involve several database calls while load method can return proxy in place and only initialize the object or hit the database if any method other than getId() is called on persistent or entity object.

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.

Strategy Design Pattern and Open Closed Principle in Java - Example

Strategy design pattern is based upon open closed design principle, the 'O' of famous SOLID design principles. It's one of the popular pattern in the field of object-oriented analysis and design along with Decorator, Observer and Factory patterns. Strategy pattern allows you to encapsulate possible changes in a process and encapsulate that in a Strategy class. By doing that your process (mainly a method) depends upon a strategy, higher level of abstraction than implementation. This makes your process open for extension by providing new Strategy implementation, but closed for modification, because the introduction of a new strategy doesn't require a change in a tested method. That's how it confirms open closed design principle.

OCAJP 8 FAQ - Oracle Certified Associate Java Programmer I Certification (1Z0–808) Frequently asked Questions

The Oracle Certifications is one of the most repeated, industry-recognized certifications. It also provides Java certifications like Oracle Certified Associate Java Programmer, also known as OCAJP and Oracle Certified Professional Java Programmer, also known as OCPJP. These two are most popular Java certification and there are many benefits of passing them e.g. better chance to get a Java development job, improved performance on Java interviews, better salary rise, and promotions, and better opportunity for moving abroad.

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

This error comes when you try to connect to the Microsoft SQL Server database from 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 Fahrenheit to Celsius in Java with Example

In this Java tutorial, you will learn how to write a program to convert Fahrenheit to Celsius in Java. Fahrenheit is a thermodynamic temperature scale, where the freezing point of water is 32 degrees Fahrenheit (°F) and the boiling point of water is 212°F (at standard atmospheric pressure). This puts the boiling and freezing points of water exactly 180 degrees apart. Therefore, a degree on the Fahrenheit scale is 1/180 of the interval between the freezing point and the boiling point of water. Absolute zero is defined as -459.67°F. If you know, in the Celsius scale, the freezing point of water is at 0ºC and the boiling point of water is at 100ºC. By using these facts, you can easily deduce a formula to convert Fahrenheit temperature into Celsius.

Top 30 Linked List Algorithm Questions from Programming/Coding Interviews

The linked list is one of the most common and essential data structure and that's why you would frequently find linked list based coding questions on interviews. The range of questions can be from simple questions like finding the length of a linked list to very difficult e.g. merging two sorted linked lists. Nevertheless, the point is that you should be familiar with linked list data structure and must know how to perform basics task in the linked list e.g. adding or removing nodes from a linked list, traversing order linked list and implementing linked list in your choice of programming language e.g. Java, C++, C, or Python.

How to use wait, notify and notifyAll in Java - Producer Consumer Example

You can use wait, notify, and notifyAll methods to communicate between threads in Java. For example, if you have two threads running in your program e.g.Producer and Consumer then producer thread can communicate to the consumer that it can start consuming now because there are items to consume in the queue. Similarly, a consumer thread can tell the producer that it can also start putting items now because there is some space in the queue, which is created as a result of consumption. A thread can use the wait() method to pause and do nothing depending upon some condition. For example, in the producer-consumer problem, producer thread should wait if the queue is full and consumer thread should wait if the queue is empty.

Is Joshua Bloch's Effective Java Still Valid in the Era of Java 8?

Effective Java is probably one of the most read books on Java technology and has been regarded by many programmers as the best book for Java developers. Though, recently many Java programmers have asked me whether Effective Java is still relevant in the era of Java 8? Or is there any better book on the same topic. The question is logical because It's been more than 9 years since the 2nd edition of Effective Java released in 2008 and also the most recent Java 8 has changed how you code Java. Many idioms and design patterns of good old days now become redundant and can be done easily with the new Java 8 syntax and feature, but does that mean "Effective Java" is not relevant now? Well, No, not at all. Effective Java is still relevant and a must-read for Java programmers due to several reasons, which you will see in this article.

2 Ways to check If String is Palindrome in Java? Recursion and Loop

A String is said to be Palindrome if it is equal to itself in reverse order. You can use this logic to check if String is Palindrome or not. There are two common ways to find if a given String is Palindrome or not in Java, first by using for loop, also known as iterative algorithm and second by using recursion, also known as recursive algorithm. The crux of this problem lies in how do you reverse String in Java? because once you have the String in reverse order, problem reduced to just comparing itself with the reversed String. If both are equal then given String is Palindrome otherwise it's not. Also whether your solution is iterative or recursive will also determine by implementing this logic.

3 Ways to Find Duplicate Elements in an Array - Java

There are multiple ways to find duplicate elements in an array in Java and we will see three of them in this program. The solution and logic shown in this article are generic and apply to an array of any type e.g. String array or integer array or array of any object. One of the most common ways to find duplicates is by using the brute force method, which compares each element of the array to every other element. This solution has the time complexity of O(n^2) and only exists for academic purposes. You shouldn't be using this solution in the real world.

Java Lock and Condition Example using Producer Consumer Solution

You can also solve the producer-consumer problem by using a new lock interface and condition variable instead of using the synchronized keyword and wait and notify methods.  The lock provides an alternate way to achieve mutual exclusion and synchronization in Java. Advantage of Lock over synchronized keyword is well known, explicit locking is much more granular and powerful than synchronized keyword, for example, the scope of lock can range from one method to another but the scope of synchronized keyword cannot go beyond one method. Condition variables are instance of java.util.concurrent.locks.Condition class, which provides inter-thread communication methods similar to wait, notify and notifyAll e.g. await(), signal(), and signalAll().

How to use Callable and Future in Java? Example

A callable interface was added in Java 5 to complement the existing Runnable interface, which is used to wrap a task and pass it to a Thread or thread pool for asynchronous execution. Callable actually represent an asynchronous computation, whose value is available via Future object. All the code which needs to be executed asynchronously goes into the call() method. Callable is also a single abstract method type (SAM type), so it can be used along with lambda expression on Java 8. Both Callable and Future are parametric types and can be used to wrap classes like Integer, String, or anything else.

Top 30 Programming questions asked in Interview - Java C C++ Answers

Top 30 Programming interview questions
Programming questions are an integral part of any Java or C++ programmer or software analyst interview. No matter which language you have the expertise it’s expected that you are familiar with the fundamentals of programming and can solve problems without taking the help of API. Programming questions like reversing String using recursion or How to find if Array contains duplicates are some popular examples of programming question in Java. Programming questions present a lot of challenges Especially to Java developers as compared to C++ programmer and I think, One reason for this is powerful Java API; Which has a method for almost every need and you rarely need to write by your own or there are lots of third-party library from Apache, Spring, Google and other open sources.

SynchronousQueue Example in Java - Produer Consumer Solution

SynchronousQueue is a special kind of BlockingQueue in which each insert operation must wait for a corresponding remove operation by another thread and vice versa. When you call to put() method on SynchronousQueue it blocks until another thread is there to take that element out of the Queue. Similarly, if a thread tries to remove an element and no element is currently present, that thread is blocked until another thread puts an element into the queue. You can correlate SynchronousQueue with athletes (threads) running with Olympic torch, they run with a torch (object need to be passed) and passes it to other athlete waiting at another end.

Top 30 Array Interview Questions and Answers for Programmers

The array is one of the most important topics for programming interviews. It doesn't matter if you are going to Google, Microsoft, Amazon or investment banks like Goldman Sachs, Barclays, Citi or even service-based companies like IBM, Accenture, TCS, or Infosys, if you are going to interview for the developer position, you must prepare array very well. In fact, it is the second most topic after String and if you look closely, may of String coding problems can be solved by treating them like character array. The array is also ubiquitous, no matter which programming language you choose, you will find array there, it's available in C, C++, Java and even on Python, Perl, and Ruby.

What is the cost of Spring Framework Certification and Training in India and USA?

One of the frequently asked questions about Spring certifications and training e.g. Spring Core and Spring Web Application Developer Certification is their cost e.g. what is the cost of Spring certification in India? or how much it cost for Spring framework certification in the USA etc. Earlier, Spring certification used to cost around 3000 USD in the USA and other North American countries and around 50,000 INR in India due to mandatory training you needed to take before you can appear in the exam. The cost of the Spring framework training was more than 90% of the total cost of the Spring certification. But gone are those days. Since 10th May 2017, you can take the exam without mandatory training, see here. Due to this reason, the cost of Spring certification has come down heavily and it's just now the cost of the exam voucher which is just 200 USD globally.

How Volatile in Java works? Example of volatile keyword in Java

How to use Volatile keyword in Java
What is a volatile variable in Java and when to use the volatile variable in Java is a famous multi-threading interview question in Java interviews? Though many programmers know what is a volatile variable they fail on the second part i.e. were to use volatile variables in Java as it's not common to have a clear understanding and hands-on on volatile variables in Java. In this tutorial, we will address this gap by providing a simple example of the volatile variable in Java and discussing some when to use the volatile variable in Java. Anyway,  the volatile keyword in Java is used as an indicator to Java compiler and Thread that do not cache the value of this variable and always read it from the main memory.

2 Examples to read Zip Files in Java, ZipFile vs ZipInputStream

ZIP format is one of the most popular compression mechanism in computer world. A Zip file may contains multiples files or folder in compressed format.  Java API provides extensive support to read Zip files, all classes related to zip file processing are located in java.util.zip package. One of the  most common task related to zip archive is to read a Zip file and display what entries it contains, and then extract them in a folder. In this tutorial we will learn how to do this task in Java. There are two ways you can iterate over all items in a given zip archive, you can use either java.util.zip.ZipFile or java.util.zip.ZipInputStream. Since a Zip file contains several items, each of them has header field containing size of items in number of bytes. Which means you can iterate all entries without actually decompressing the zip file.

Difference between Inheritance and Composition in Java and Object Oriented Programming

Though both Inheritance and Composition provide code reusability, the main difference between Composition and Inheritance in Java is that Composition allows reuse of code without extending it but for Inheritance, you must extend the class for any reuse of code or functionality. Another difference that comes from this fact is that by using Composition you can reuse code for even the final class which is not extensible but Inheritance cannot reuse code in such cases. Also by using Composition, you can reuse code from many classes as they are declared as just a member variable, but with Inheritance, you can reuse code from just one class because in Java you can only extend one class because multiple Inheritance is not supported in Java.

How to access Private Field and Method Using Reflection in Java

Reflection in Java is very powerful feature and allows you to access private method and fields which is not possible by any other means in Java and because of this feature of reflection many code coverage tool, static analysis tool and Java IDE like Eclipse and Netbeans has been so helpful. In last article we have seen details about private keyword in Java and learned  why we should always make fields and method private in Java. There we have mentioned that private fields and methods are only accessible in the class they are declared but with reflection you can call private method and access private fields outside the class. In this article we will see simple example of accessing private field using reflection and invoking private method using reflection in Java.

How to differentiate between an Average and a Good Programmer?

When it comes to interview, goal is to find the most suitable developer for job to get done but its very difficult to judge someone's caliber, experience and expertise in short duration of Interview. There is always a process starting from phone interview, written tests to face-to-face interview, but its still difficult to hire the right programmer. Process can help you to filter candidates but eventually it will come down to your experience and gut feeling. As you take more and more interviews, you will know what to ask and what not and like many other interviewers in the world, you will develop some of your own tips. Similarly, I have developed couple of tips from my experience which has helped me to differentiate an average programmer with a good programmer in past.

Can you take Spring Professional Certification without Training Course?

Yes, you can take Spring certification without taking mandatory Spring training. Pivotal, the company behind Spring, has announced on 10th May 2017 that "Spring Certification Exams are now available for individual purchase, without enrolling in the course". This is one of the most exciting changes in the Spring certification program since it's launched 10 years back. The cost of Spring certification was the single, biggest obstacle for many experienced Java and Spring developers to get certified for their Spring framework skills. This step from Pivotal is a really positive step and gives a real chance to many experienced developers in cost-sensitive countries like India to get certified for their skills.

How to print 1 to 100 without using loop in Java

This is one of the interesting problems  I have seen on coding interviews  for beginners. The program has surprise element by saying that you need to print 1 to 100 without using a loop e.g. for, forEach or enhanced for loop. This brings out some innovative solutions from candidates which tell a lot about their approach, knowledge, and attitude. I remember, asking this question during campus recruitment to at least 5 candidates. The first one took 5 minutes to think and then come up with the brute force way where he just copies pasted 100 System.out.println() and printed number 1 to 100 but when we asked to improve that, he couldn't too that. Unfortunately, he didn't think that recursion can replace an iterative algorithm without using a loop.

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

PDF format is a popular format for sending receipt, email confirmation and other documentation and we often has requirement to create PDF documents using Java, mostly in JSP pages. Since most of official documentation uses PDF format now days, it becomes imperative to support PDF files. Recently I received couple of question regarding 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 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.

Which Java 8 Certification Should you Take? OCAJP8 (1Z0-808) , OCPJP8 (1Z0-809) , or Upgrade(1Z0-810 and 1Z0-813)

There are a lot of confusion among Java programmers and Oracle Java Certification aspirants related to various Java 8 certifications e.g. what are exam codes, which exams they should go for, whether they are eligible for Java SE 8 upgrade exams, and what should they do if they have just passed Java SE 7 Programmer II certification. I will try to answer each of these questions here, but to get it right let's first clear the confusion about various Java SE 8 exams There are four Java 8 certifications available in Oracle's site:

1) Oracle Certified Associate, Java SE 8 Programmer OCAJP8, exam code 1Z0-808
2) Oracle Certified Professional, Java SE 8 Programmer OCPJP8, exam code 1Z0-809
3) Oracle Certified Professional, Java SE 8 Programmer (upgrade), exam code 1Z0-810
4) Upgrade to Java SE 8 OCP ( Java SE 6 and all prior versions) - exam code 1Z0-813

Top 5 Cloud Computing Platforms Java Programmers and Developers Should Know

Cloud computing is Hot, it's the biggest IT trend of the last few years and will continue to grow strong in the coming future. Cloud computing provides several not-so-easy-to-ignore advantages, especially to public and small enterprises, which cannot afford to own and maintain expensive data centers. Since most online businesses nowadays need high availability, scalability, and resiliency, with-in a quick time, it's not possible to achieve all these on your own, and cloud computing becomes the best alternative here. Cloud service providers like Amazon Web Services (AWS) has helped several firms to remain focus on their business, without worrying for IT and infrastructure too much, this has yield big result for them.

Difference between Transient, Persistent, and Detached Objects in Hibernate

In the Hibernate framework, an entity can be in three states, transient, persistent, and detached. When an object is in a transient state, it is commonly referred to as a transient object, similarly, if it is in persistence and detached state, it is known as a persistent and detached object. When an entity is first created using the new operator e.g. new User() and not associated with Hibernate session e.g. you haven't called session.save(user) method then it is known as a transient object. At this stage, Hibernate doesn't know anything about this object and the object doesn't have any representation in the database e.g. a corresponding row in the User table.

Difference between CAST, CONVERT, and PARSE function in Microsoft SQL Server

Though all three, CAST, CONVERT, and PARSE are used to convert one data type into another in SQL Server, there are some subtle differences between them. The  CAST method accepts just two parameters, expression, and target type, but CONVERT() also takes a third parameter representing the format of conversion, which is supported for some conversions, like between character strings and date-time values. For example, CONVERT(DATE, '2/7/2015', 101) converts the character string '2/7/2015' to DATE using DATE format 101, representing United States standard.

Top 10 Google Interview Questions for Software Engineer - Books, Resources

These Google interview questions are some of my favorites collected from different sources. Every Programmer knows that Google is one of the best technology companies and its dream for many software developers to work for Google, but at the same time interview process at Google is very tough and only a few genuine intelligent programmers get through their interview process. Google interview questions have always been a good topic of discussion when few young software developers gathered around, I can still remember when one of my friends got a call from google for an interview then how the whole bunch was got excited.

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 number 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.

Log4j Tips : Use MDC or Mapped Dignostic Context to distinguish logging per Client or Request

The MDC or Mapped Diagnostic Context is a concept or feature of 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.

Difference between ArrayList and ArrayList<?> in Java - Raw Type vs Wildcard

One of my readers asked me about the difference between ArrayList vs ArrayList< in Java?>, which was actually asked to him on 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 looks very similar. If a method accepts ArrayList or ArrayList<?> as a parameter then it can accept any type of ArrayList e.g. ArrayList of String, Integer, Date, or Object, but if you look closely you will find that one is raw type while 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

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 does hide something, but the key difference is on intent.

10 Examples of Optional in Java 8

Null is bad, it can crash your program. Even it's creator called it a billion-dollar mistake hence you should always try to avoid using nulls whenever you can. For example, you should not return a null String when you can return an empty String, similarly never return null collections when you can return an empty collection. I have shared many such tips in my earlier article, 10 tips to avoid NullPointerException and my reader liked that a lot. But, I wrote that article a couple of years ago when Java 8 was not around and there was no Optional, a new way to avoid NullPointerException in Java, but, things have changed now.

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

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? Anyway, It gives me an opportunity to recap some of the other technique (syntactically) to prevent a method from being overridden and write this blog post to share some mystery tricks from Java world. Some of you might be aware of those non obvious way to prevent method overriding, but if you don't, here is your opportunity to learn.

2 Free Oracle Certified Master Java Enterprise Architect (OCMJEA) 6 Mock Exams - 1Z0-807

The OCMJEA 6 or Oracle Certified Master Java Enterprise Architect Java EE 6 is one of the most respected Java certification. It is also the most toughest Java exam currently available. In order to get this certification, you need to pass not just one but a couple of exams, submit assignments and essays and also have to complete a mandatory training. The Java EE 6 Enterprise Architect Certified Master 1Z0-807 exam is the start of it. Once you pass this exam, you need to complete Java (EE) Enterprise Architect Certified Master Assignment (1Z0-865) and Java (EE) Enterprise Architect Certified Master Essay (1Z0-866) exams. After successfully completing these exams, you need to attend one mandatory training from the list of training programs, only then you will be awarded the Oracle Certified Master certification. Though, it's not necessary to take the training after completing exams, if you like, you can choose a relevant training which can help you to prepare well for OCMJEA 6 certification and take that first before appearing for any exam.

5 Reasons Why Java's old Date and Calendar API was Bad

If you have been programming in Java for a couple of years then you may know that how bad was Java's Date and Calendar API was, I mean the java.util.Date and java.utill.Calendar was badly designed. Though Java has corrected it's mistake by introducing a brand new, shiny Date and Time API, not many Java developers are using it yet. In a bit to motivate you to use new Date and Time API from Java 8, I am going to list down a couple of reasons why Java's Date and Calendar class has been criticized so much in the past.  These points are also important to know from the Interview point of view because as an experienced Java programmer, it is expected from you to know the shortcomings of existing API and how new API solves those problems.

FizzBuzz Solution in Java 8 - The Best way to learn Functional Programming in Java

FizzBuzz is one of the most famous programming questions from interviews, which is generally used to weed out programmers who can't program. The problem is deceptively simple but you can't solve it if you don't know how to build programming logic. I love it just for its simplicity. Now coming back to the second part of this article, Java 8. It's been more than a year, I think it was March 18 last year when Java 8 was first released and to date, the most common question I have got is, how to learn new features of Java 8? like Optional, lambda expression, or Stream. I think the best way to learn Java 8 new features is the same as the best way to learn any new programming language like solving common coding problems, implementing data structure, common algorithms, and implementing famous design patterns.

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.

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 as a 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.

How Garbage Collection works in Java

I have read many articles on Garbage Collection in Java, some of them are too complex to understand and some of them don’t contain enough information required to understand garbage collection in Java. Then I decided to write my own experience as an article. You can call it a tutorial about garbage collection in simple words, which would be easy to understand and have sufficient information to understand how garbage collection works in Java. Garbage collection works by employing several GC algorithms like Mark and Sweep, G1, etc. There are different kinds of garbage collectors available in Java to collect different areas of heap memory like you have serial, parallel, and concurrent garbage collectors in Java.

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 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 method 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.

2 Examples of Streams with Collections in Java 8

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 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 this, you can filter elements of collection on a given criterion e.g. if you have a list of orders, you can filter buy orders with sell orders, filter orders based upon there quantity and price, and so on.

Difference between First and Second Level Cache in Hibernate

If you have used Hibernate in past then you know that one of the strongest points of the Hibernate framework is caching, which can drastically improve the performance of Java application's persistence layer if configured and used correctly. Hibernate provides caching at many levels e.g. first level cache at Session level, second-level cache at the SessionFactory level, and query cache to cache frequently executed SQL queries. The first level cache minimizes database access for the same object. For example, if you call the get() method to access Employee object with id = 1 from one session, it will go the database and load the object into memory, but it will also cache the object in the first-level cache.

How to Convert an Array to Comma Separated String in Java

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 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 array or collection and returns a String where each element is joined by a delimiter.

10 Hibernate Interview Questions and Answers for Java Developers

Hibernate Interview Questions are asked on Java J2EE Interviews, mostly for web-based enterprise application development role. Success and acceptability of Hibernate framework on Java world have made it one of the most popular Object Relational Mapping (ORM) solution in the Java technology stack. Hibernate frees you from database-specific coding and allows you to focus more on utilizing powerful object-oriented design principles to implement core business logic. By using Hibernate you can switch between database rather easily and also take advantage of out of box caching facilities provided by Hibernate, in terms of second-level cache and query cache.

How to Clone Collection in Java - Deep copy of ArrayList and HashSet

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

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.

Top 50 Java Thread Interview Questions Answers for Experienced

You go to any Java interview, senior or junior, experience or freshers,  you are bound to see a couple of questions from the thread, concurrency, and multi-threading. In fact, this built-in concurrency support is one of the strongest points of Java programming language and helped it to gain popularity among the enterprise world and programmers equally. Most of the lucrative Java developer position demands excellent core Java multi-threading skills and experience in developing, debugging, and tuning high-performance low latency concurrent Java applications. This is the reason, it is one of the most sought after skills in Java interviews. The multithreading and concurrency are also hard to master the concept and only good developers with solid experience can effectively deal with concurrency issues.

How to Implement Stack in Java Using Array and Generics - Example

The stack is one of the popular data structures which supports LIFO (Last In First OUT) operation. Due to the LIFO advantage, you can use a stack data structure to convert a recursive algorithm to an iterative one. The stack data structure is very easy to implement using an array or linked list, but you don't have to implement it on your own because Java already provides a Stack implementation in java.util.Stack class. This class is a subclass of the Vector class and you should use it whenever you need Stack for your production code, there is no point in inventing the wheel again when the focus is on developing your application.

130+ Java Interview Questions Answers for 2 to 7 Year Experienced Programmers

Last Updated Date: 2nd March 2018
Time is changing and so is Java interviews. Gone are the days, when knowing the difference between String and StringBuffer can help you to go through the second round of interview, questions are becoming more advanced and interviewers are asking more deep questions. When I started my career, questions like Vector vs Array and HashMap vs Hashtable were the most popular ones and just memorizing them gives you a good chance to do well in interviews, but not anymore. Nowadays, you will get questions from the areas where not many Java programmer looks e.g. NIO, patterns, sophisticated unit testing or those which are hard to master e.g. concurrency, algorithms, data structures and coding.