JDBC - How to get Row and Column Count From ResultSet in Java? Example

One of the common problems in JDBC is that there is no way to get the total number of records returned by an SQL query. When you execute a Statement, PreparedStatement, or CallableStatement using execute()or executeQuery() they return ResultSet and it doesn't have any method to return the total number of records it is holding. The only way to find the total number of records is to keep the count while you are iterating over ResultSet while fetching the result. This way, you can print the total number of rows returned the SQL query but only after you have processed all records and not before, which may not be the right way and incur significant performance cost if the query returns a large number of rows.

Can You Create Instance of Abstract class in Java? Answer

Hello Java Programmers, how are you doing? Hope you are doing well. It's been a long since  I shared a core Java interview question in this blog, so let's start with that. Earlier I have shared one of the frequently asked questions in Java, can we make an abstract class final in Java and my readers really liked it and asked for more such questions. So, today I am going to talk about whether you can create an instance of an Abstract class in Java or not? This is another interesting core Java question that you will find on telephonic interviews, a written test that has multiple-choice questions and most notably Oracle certified Java programmer certification like OCAJP 8  and OCAJP 11.

How to convert String to Enum in Java? ValueOf Example

valueOf Example in Java Enum

valueOf method of Java Enum is used to retrieve Enum constant declared in Enum Type by passing String in other words valueOf method is used to convert String to Enum constants. In this Java Enum valueOf example we will see how to use the valueOf method in Java. valueOf method is implicitly available to all Java Enum because every enum in Java implicitly extends java.lang.Enum class. valueOf method of enum accepts exactly the same String which is used to declare Enum constant to return that Enum constant. valueOf method is case-sensitive and invalid String will result in IllegalArgumentException.

The Ultimate Guide to Package in Java? Examples

If you are learning Java then you might have come across a package concept and if you are wondering what is package and why should we use it then you have come to the right place. In this article, I will explain what is package in Java and other stuff around the package, including some best practices which using the package in Java. In the simplest form, a package is a way to organize related functionality or code in a single place in Java. If you look from a File System perspective then a package in Java just represent a directory where Java source file is stored in compilation and class files are stored after compilation. 

How to read a file line by line in Java? BufferedReader Example

Hello Java Programmers, if you are looking for a way to read a file line by line in Java then don't worry, Java provides java.io  package in JDK API for reading File in Java from File system e.g. C:\ or D:\ drive in Windows or any other directory in UNIX. First, you can use FileInputStream to open a file for reading. FileInputStream takes a String parameter which is a path for the file you want to read. Be careful while specifying File path as path separator is different on Window and UNIX. Windows uses backslash while UNIX uses forward slash as a path separator. 

Java Enum with Constructor Example

Java Enum with Constructor

Many Java developers don't know that Java Enum can have a constructor to pass data while creating Enum constants. This feature allows you to associate related data together. One example of passing arguments to enum Constructor is our TrafficLight Enum where we pass the action to each Enum instance e.g. GREEN is associate with go, RED is associated with stop, and ORANGE is associated with the slow down. 

Could not create the Java virtual machine Invalid maximum heap size: -Xmx

"Could not create the Java virtual machine" is a general JavaVirtual Machine error when you run java command directly or indirectly and it's not able to create a virtual machine because of invalid maximum heap size, invalid minimum heap size, or just an error in command line. This error not only come when you run Java program from the command line but also when you run them using any IDE like Eclipse or Netbeans.

ArrayList vs Vector in Java? Interview Question Answer

ArrayList vs Vector in Java
ArrayList and Vector are the two most widely used Collection classes in Java and are used to store objects in an ordered fashion. Every Java programmer which is introduced to Java Collection Framework either started with Vector or ArrayList. For beginners Difference between Vector and ArrayList in Java and LinkedList vs ArrayList are the two most popular Java Interview questions. ArrayList vs Vector is not only important from an interview perspective but also on the effective use of Java Collection API. 

The Ultimate Guide of Enum in Java - Examples

Apart from the Class and Interface, Enumeration type or Enum is another popular type in Java programming language. Enum allows you to represent a fixed number of well-known things in a type-safe manner e.g. days of the week, days of the month, planets in the solar system, buttons on the remote control, keys on the keyboard, and suits on playing cards. Before Enum was introduced, prior to Java 1.5, integer and string constants are used to represent the fixed number of things, known as enum int pattern and enum string pattern as described in classic Effective Java by none other than Joshua Bloch. Though they served the purpose, they had some major drawbacks which resulted in poor quality code.

What is class file in Java? Example

What is the class file in Java?
Class file in Java is compiled from of Java source file. When we compile a Java program written in a Java source file ended with a .java extension, it produces one more class file depending upon how many classes are declared and defined in that Java source file. One Java source file can only contain one public class, and its name must match with the name of the file like HelloWorld.java file can contain a public class whose name should be HelloWorld as shown below :

Difference between static and non static nested class in Java? Example

Static vs. non Static class in Java

In Java, you can make a class either static or non-static. Now, what is the difference between making a class static vs. non-static? Well, there is a lot of difference between them. First of all, there are two kinds of classes in Java, one is called a top-level class, and the other is called a nested class. As the name suggested, a top-level class is a class that is declared in the .java file and not enclosed under any other class. On the other hand, a nested class is declared inside another class. The class which enclosed nested class is known as Outer class. 

How to read file in Java using Scanner Example - text files

Reading a file with Scanner

From Java 5 onwards java.util.Scanner class can be used to read file in Java. Earlier we have seen examples of reading file in Java using FileInputStream and reading file line by line using BufferedInputStream and in this Java tutorial, we will See How can we use Scanner to read files in Java. Scanner is a utility class in java.util package and provides several convenient methods to read int, long, String, double etc from a source which can be an InputStream, a file, or a String itself.

Difference between throw vs throws in Java? Answer

throw vs throws in Java

throw and throws are two Java keywords related to the Exception feature of the Java programming language. If you are writing a Java program and familiar with What is Exception in Java, it's a good chance that you are aware of What is throw and throws in Java. In this Java tutorial, we will compare throw vs throws and see some worth noting differences between throw and throws in Java. Exception handling is an important part of the Java programming language which enables you to write robust programs. There are five keywords related to Exception handling in Java like try, catch, finally, throw, and throws.

How to read User Input from Console in Java? Scanner Example

Apart from reading files, Scanner can also read user input from Console in Java. Just like in the case of reading files, we have provided File as a source for scanning, We need to provide System.in as a source to scan for user input in Console. Once you created and initialized java.util.Scanner, you can use its various read method to read input from users. If you want to read String, you can use nextLine(), if you want to read integer numbers, you can use nextInt(). 

How to Find IP address of localhost or a Server in Java? Example

In today's Java programming tutorial, we will learn some networking basics by exploring the java.net package. One of the simple Java network programming exercises, yet very useful, is to write a program to find the IP address of the local host in Java. Sometimes this question is also asked to find the IP address of the Server on which your Java program is running or find the IP address of your machine using Java etc. In short, they all refer to localhost. For those who are entirely new in the networking space, there are two things to identify a machine in a network, which could be LAN, WAN, or The Internet. 

15 People Java Developers Should Follow on Twitter

If you are passionate about Java and would like to follow Java bloggers into Twitter then here is my list of 15 people you can follow on Twitter to keep yourself up-to-date and engage in the Java world. These people regularly share the latest things in Java, JVM, Spring, Hibernate, and other Java technology. By following them, you will not only know about their latest work but also what's happening in the Java world. You might be thinking just 15 people, well, there are many more who is not on this list but I regularly share their Twitter handles via my Twitter account @javinpaul and @Javarevisited. If you are following me then you will automatically get to know about them.

Java Keyword Cheat Sheet - Meaning and Usage

Knowing keywords of a programming language is very important to understand its features, and Java has rich set of keyword, going along with rich set of functionalities. The first keyword, I learn while writing Java program was public, static and void, not surprisingly they are picked from main method. Our instructor explained meaning of each keyword, saying that its, always remember why main is public, static and void main Java. 

Video example - Dijkstra's Algorithm shortest path in Graph

Video example - Dijkstra's Algorithm shortest path in Graph

Dijkstra's Algorithm in Graph theory allows you to find least cost path or shortest path between two nodes in directed and weighted graph. Dijkstra's Algorithm is one of the important concept of Graph theory and often asked in Exams and interviews. Frankly speaking Its not easy to understand Dijkstra's Algorithm , at least until you have a good example and this leads me to search for simple and easy to learn example of Dijkstra's Algorithm which landed me on this video. I have earlier shared Graph traversal BFS and DFS algorithm from this same author and when I found his video on Dijkstra's Algorithm, I knew this is going to be another best. By the way Dijkstra's Algorithm has several practical usage like finding shortest path between cities for Air planes route or bus route as cities and driving path between cities fits nicely

as vertices of Graph and directed and weighted path between them. In Dijkstra's Algorithm , path between two nodes which are unreachable directly is assumed as infinity. I suggest watching this video example more than one time if you are unsure how Dijkstra's Algorithm works.

How to remove duplicate(s) from linked list in Java? Example Tutorial

Hello guys, if you are wondering how to find duplicates in a given linked list in Java then you have come to the right place. In the past, I have explained how to reverse a linked list in Java, find kth element from tail in linked list, find cycle on linked list, and in this article, I will show you how to find duplicate nodes in a given linked list. This is one of the classic linked list coding problem and I have also included this in my list of 30 common linked list problems for programmers. You can further check that list to practice more linked list programs and improve your understanding of linked lists and how to solve those problems. But, before we get into details of finding and printing duplicate nodes from the given linked list let's start with the basics. 

How to find Factorial in Java using Recursion and Iteration - Example Tutorial

Hello guys, if you are looking for a Java program to calculate factorial with and without recursion then you have come to the right place. Factorial is a common programming exercise that is great to learn to code and how to program. When I teach Java to new people, I often start with coding problems like prime numbers, Fibonacci series, and factorial because they help you to develop a coding sense and teach you how to write a program initially. In order to calculate factorial, you just need to know the factorial concepts from Mathematics, and rest I will explain this simple Java programming tutorial.