4 Example to Iterate over Map, HashMap, Hashtable or TreeMap in Java

There are multiple ways to iterate, traverse or loop through Map, HashMap, or TreeMap in Java and we are all familiar with either all of those or some of those. But to my surprise, one of my friends was asked in his interview (he has more than 6 years of experience in Java programming) to write code for getting values from HashMap, Hashtable, ConcurrentHashMap, or TreeMap in Java in at least 4 ways. Just like me he was also surprised by this question but written it. I don't know why exactly someone asks this kind of java interview question to a relatively senior java programmer. Though my closest guess is to verify that whether he is still hands-on with coding in java. 

10 Examples of HashSet in Java - Tutorial

HashSet in Java is a collection that implements the Set interface and is backed by a HashMap. Since HashSet uses HashMap internally it provides constant-time performance for operations like add, remove, contains and size give HashMap has distributed elements properly among the buckets. Java HashSet does not guarantee any insertion orders of the set but it allows null elements. HashSet can be used in place of ArrayList to store the object if you require no duplicate and don't care about insertion order.

Difference between bitwise and logical AND, OR Operators in Java? Examples

Java beginners often ask the same type of questions, and of them is what is the difference between & and && operator in Java or the difference between | and || operators? The standard answer to this question is well, the main difference between & and && is that the former is a bitwise operator, and && is a logical operator in Java. That's academic until you clearly explain the difference in working of & and && or | and ||. For absolute beginners, & is used to represent AND logic operation in Java and | is used to represent OR logic operation.

What is NavigableMap in Java ? TreeMap, headMap, tailMap, and subMap Examples

Hello guys, if you are wondering what is NavigableMap and why should Java developer know about it you are at right place. NavigableMap in Java is an extension of SortedMap  like TreeMap which provides convenient navigation methods like lowerKey, floorKey, ceilingKey, and higherKey. NavigableMap is added on Java 1.6 and along with these popular navigation methods it also provides ways to create a Sub Map from existing Map in Java, like headMap whose keys are less than the specified key, tailMap whose keys are greater than specified key and a subMap which strictly contains keys that falls between toKey and fromKey. 

Why use SerialVersionUID inside Serializable class in Java? Example

Serialization and SerialVersionUID always remain a puzzle for many Java developers. I often see questions like what is this SerialVersionUID, or what will happen if I don't declare SerialVersionUID in my Serializable class? Apart from the complexity involved and rare use, one more reason for these questions is Eclipse IDE's warning against the absence of SerialVersionUID e.g. "The Serializable class Customer does not declare a static final SerialVersionUID field of type long". In this article, you will not only learn the basics of Java SerialVersionUID but also its effect during the serialization and de-serialization process. 

Object Oriented Programming Example in Java? Tutorial

I remember when I was doing my engineering, the OOPS concept was in the first semester. Back then it looks like some alien things to me, because I have never done programming and even the smallest program we get to write like checking whether the number is palindrome or not, or printing the Fibonacci series, we never really needed to use OOPS. When needed, I just memorize things and write them down in exams :). That worked, I passed the exam but effectively I didn't learn OOP or Object Oriented Programming on those days.

Difference between Checked vs Unchecked Exception in Java? Example

Checked and Unchecked Exception is two types of Exception exist in Java. Though there is no difference in functionality and you can very achieve the same thing with either checked Exception or Unchecked Exception, there is some difference on exception handling part. In this Java tutorial we will see what is checked and Unchecked Exception in Java, Examples of Checked and Unchecked Exception and most importantly we will learn when to use Checked Exception and when to use Unchecked Exception in Java and lastly we will see the difference between checked and unchecked exception to understand things better. 

[Solved] How to solve java.lang.UnsatisfiedLinkError: no ocijdbc11 in Java with Oracle 11g, 12c, 19c and 21c

"java.lang.unsatisfiedlinkerror no ocijdbc11 in java.library.path" error comes when you try to connect to Oracle 11g database using OCI (thick) driver by using tns name, but the ocijdbc11.dll file is not available in PATH or java.library.path environment variable. ocijdbc11.dll is a native library and if you know Java searches native library in PATH or a location specified by java.library.path system property, if it doesn't find the dll, then it throws java.lang.unsatisfiedlinkerror no ocijdbc11 in java.library.path error. This dll is usually found in C:\Programs\Oracle\ora11g\bin\ocijdbc11.dll, but it could vary depending upon your Oracle installation.

How to fix java.lang.UnsupportedClassVersionError: Bad version number in .class files? Example

How to fix Bad version number in the .class file

"java.lang.UnsupportedClassVersionError: Bad version number in .class file" is a common error in Java programming language which comes when you try to run a Java class file which was compiled by different version of Java compiler than then JRE version you are using to run it. In our last article, we discussed that how to resolve Java.lang.UnSupportedClassVersionError and found that it comes when a major and minor version of the class is not supported by Java virtual machine or JRE running the program. Though "java.lang.UnsupportedClassVersionError: Bad version number in .class file" is a little different than that of its manifestation and Cause, both are related to the mismatch in compiler javac and runtime java version. 

How to Fix Must Override a Superclass Method Error Eclipse IDE Java | @Override annotation with interface methods

One of the annoying error while overriding Java method in Eclipse IDE is must override a superclass method error, This error is quite frequent when importing Java projects and after so long, still I haven't seen any permanent solution to it. Must override a superclass method the error comes in Eclipse if you have Java Class that implements interface and overrides a method from interface and uses @Override annotation. Unfortunately, Eclipse defaults to Java 1.5, which only recognize @Override annotation for the overriding method from the superclass and not from the interface.

How to fix "No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK" in Eclipse & Maven?

If you are like many Java developer who uses Maven and Eclipse to build Java project using M2Eclipse plugin, you might have seen this error before. I ran into it recently when I ran the Maven Install command for one of the Java projects, configured as Maven project,  only to realize that Maven builds failed after throwing this error. The main reason for this error is that Maven is not able to find javac (the Java compiler) which is required to compile Java source files. If you remember, the javac command comes in the bin directory of JDK, hence, you need a JDK installation in your local machine to compile the Java project.

How to fix java.sql.SQLException: Invalid column index? Example

"java.sql.SQLException: Invalid column index" is a frequent error while working in Java Database Connectivity (JDBC). As the name suggests "Invalid column index" its related to accessing or setting column in your SQL Query using prepared statement in Java. I have seen "java.sql.SQLException: Invalid column index" coming mostly due to two reason:

1) Setting column data using setXXXX(int coloumIndex) e.g. setInt(0) setString(0)

2) Getting column data using getXXX(int columnIndex) e.g. getInt(0) getString(0)

The most common cause of "java.sql.SQLException: Invalid column index" is a misconception that column index started with "0" like array or String index but that's not true instead column index starts with "1" so whenever you try to get or Set column data with column index "0" you will get "java.sql.SQLException: Invalid column index".

How to become Blockchain Architect in 2024? Is Blockchain Architecture Certification by 101 Blockchains worth it?

Blockchain solutions have been making a lot of noise in the tech space recently for all the right reasons. It comes with the advantage of decentralization, security, and transparency. At the same time, you can also notice the possibility of a growing ecosystem of use cases. A Certified Enterprise Blockchain Architect can serve as a promising asset for enterprises in the present times. How? The work of an architect focuses on designing blockchain solutions by evaluating the requirements of the specific use case.

How to learn Metaverse from scratch? Is Certified Metaverse Professional (CMP) on 101 Blockchains worth it

Is Certified Metaverse Professional (CMP) on 101 Blockchains worth it?
Hello guys, if you want to learn Metaverse in 2022 and wondering how to learn Metaverse then you have come to the right place. Earlier, I have shared best Metaverse online courses and in this article, I am going to review one of the popular Metaverse certification, The certified Metaverse Professional certification from 101 Blockchains, one of the leading portal for Blockchain, Web3, NFT, and Metaverse training. The Metaverse is the next big thing, and you must have heard this a million times, just like many tech enthusiasts. The diverse elements of the metaverse have the potential to grab the attention of every person on the planet. Many big companies have already placed their stakes in the metaverse. 

How to use ArrayList in Java? 10 Examples of ArrayList

ArrayList in Java is the most frequently used collection class after HashMap in Java. Java ArrayList represents an automatic re-sizeable array and used in place of the array. Since we can not modify the size of an array after creating it, we prefer to use ArrayList in Java which re-sizes itself automatically once it gets full. ArrayList in Java implements the List interface and allows null. Java ArrayList also maintains the insertion order of elements and allows duplicates opposite to any Set implementation which doesn't allow duplicates. ArrayList supports both the Iterator and ListIterator for iteration but it’s recommended to use ListIterator as it allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the Iterator's current position in the list.