Core Java Tutorials

“Core Java” is Sun’s term, used to refer to Java SE, the standard edition and a set of related technologies, like the Java VM, CORBA, etc. This is mostly to differentiate from others like Java ME or Java EE. “Core Java” is Oracle’s definition and refers to subset of Java SE technologies.

The Core Java technologies and application programming interfaces (APIs) are the foundation of the Java Platform, Standard Edition (Java SE). They are used in all classes of Java programming, from desktop applications to Java EE applications.

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Regex Boundary Matcher: Matching Begin-with / End-with

Java regex word boundary example. Use regular expression word boundaries to find matching lines which start with or end with a certain words.

Java Regex to Match Misspell Words

Java example of matching all common misspellings of any word in text content.

Java Delete Temporary File

Learn how to delete a temporary file in Java. We will see examples to use File.deleteOnExit() and File.delete() methods.

Java Create Temp File or Directory

Learn to create a temp file and directory in Java using the legacy and NIO classes. Also, learn to delete temp files or temp directories on JVM shutdown.

Writing to Temporary File in Java

Learn to create a temporary file and write to it in Java. We will use the code sample used for creating a temporary file example.

Check If a File or Directory Exists in Java

Learn to check if a file exists or a directory exists in given path in Java. Also check is file is readable, writable or executable.

Convert String to InputStream in Java

Java example to convert String to InputStream using ByteArrayInputStream and IOUtils classes. Writing String to InputSteam is a frequent job .

Read File to Byte[] in Java

Learn reading data from files into a byte array in Java using NIO Files, FileInputStream, Commons IO FileUtils, and Guava ByteStreams classes.

Reading and Writing UTF-8 Data into File

Learn reading and writing UTF-8 content into a file using BufferedReader and BufferedWriter in Java.

Java Memory Model – Structure and Components

Whenever we execute a Java program, a separate memory area is reserved for storing various parts of our application code which we roughly call JVM memory. Though not necessary, having some knowledge about the structuring of this memory area is quite beneficial. Knowing Java memory model becomes more important when …

OpenCSV – Read and Write CSV Files in Java

Learn how to read CSV file and write data to CSV file in Java. We will use opencsv library which provide excellent support to work with CSV files in Java.

HiLo Guessing Game in Java

In HiLo game, we have to adjust our next guess such that we are able to guess the right number within six attempts. Learn with a Java program.

Guide to Java LineNumberReader

For reading a file line by line, the LineNumberReader class could be used that allows to keep track of which line we are currently processing.

Java Read and Write Properties File Example

Learn to read property file in java using Properties.load() method. Then we will use Properties.setProperty() method to write a new property into file,

Reading User Input from Console in Java

Learn to read the user input from the console in Java and write to the console using Console, BufferedReader and Scanner with examples.

Java FileFilter (with Examples)

Java FileFilter accepts File objects and thus can be used to filter the files based on other attributes such as read-only, directory etc.

Read an XML File using DOM Parser in Java

Learn to read or parse XML documents into String, write to files and convert to POJO using Java DOM parser API with examples.

Difference between DOM and SAX Parser

Both DOM and SAX parsers are extensively used to read and parse XML files in java applications and both of them have their own set of advantages and disadvantages.

Java – Read and Write PDF with iText

In this iText tutorial, we are writing various code examples to read a PDF file and write a PDF file. iText library helps in dynamically generating the .pdf files from Java applications. The given code examples are categorized into multiple sections based on the functionality they achieve. With each example, …

Localized Currency Formatting in Java

Most of the applications today, which are targeted at a larger audience e.g. internet users, usually deal in money as well. In such applications, a requirement will be to display money/currency in a format specific to that location or country. In this tutorial, I am giving some examples that will …

Getting Current Locale in Java

Learn to get the locale of the user in Java that is used to format the content according to the user’s demographics (geographical, political, or cultural information). 1. What is Locale? Suppose we are developing an application and we are asked to make the application customized for international end-users. To …

How does Deserialization happen in Java?

Deserialization in Java is the process by which the object previously serialized is reconstructed back into its original form i.e. object instance.

Java Generics PECS – Producer Extends Consumer Super

Learn about Java Generics PECS which is related to producing and consuming collections with easy-to-follow examples.

Java Method Overloading vs. Method Overriding

Learn the difference between method overloading and method overriding in java, which mainly involve method name, signature, parameters list and return type.

Java transient keyword example

The Java transient keyword is used on class attributes/variables to indicate that serialization process of such class should ignore such variables while creating a persistent byte stream for any instance of that class. A transient variable is a variable that can not be serialized. According to Java Language Specification [jls-8.3.1.3] …

Difference between 32-bit Vs. 64-bit Java

In computer architecture, 64-bit computing is the use of processors that have datapath widths, integer size, and memory addresses widths of 64 bits (eight octets/bytes). Also, 64-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. From the software perspective, …

Java Generics Tutorial

Java Generics is a technical term denoting a set of language features related to the definition and use of generic types and methods.

Java Compare and Swap Example – CAS Algorithm

One of the best additions in java 5 was Atomic operations supported in classes such as AtomicInteger, AtomicLong etc. These classes help you in minimizing the need of complex (un-necessary) multi-threading code for some basic operations such as increment or decrement a value which is shared among multiple threads. These …

Java Reflection – Real Usage Examples

Reflection is one of those things like multi-threading where everyone with experience of it says “Don’t use it unless you absolutely have to”. Above quote is absolutely true for all for us alike. In my previous tutorial, I discussed basics of annotation in which I discussed the usage of reflection …

Complete Java Annotations Tutorial

An annotation is a kind of metadata in Java that can be applied to various elements of Java source code so that later some tool, debugger, or application program can take advantage of these annotations; and help analyze the program in a positive and constructive way. Just to mention, we …

Difference between HashMap vs Hashtable in Java

At entry level Java programmer, you can expect this interview question on Hashtable vs HashMap. Though the question becomes really easy when you know other concepts like how hashmap works, yet after getting a many queries from my blog readers who are preparing for or working at junior level, I …

Java ASCII to Hex Conversion (and vice-versa)

ASCII (American Standard Code for Information Interchange) is a character encoding standard that assigns numerical values to characters. Each character is represented by a unique numerical value ranging from 0 to 127. Similarly, Hexadecimal (or hex) is a base-16 numbering system that uses 16 distinct symbols: 0-9 and A-F (or …

Java Concurrency – Difference between yield() and join()

Multi-threading is very popular topic among interviewers from long time. Though I personally feel that very few of us get real chance to work on a complex multi-threaded application (I got only one chance in last 7 years), still it helps in having the concepts handy to boost your confidence …

Java Concurrency – Thread Safety?

Defining thread safety is surprisingly tricky. A quick Google search turns up numerous “definitions” like these: Thread-safe code is code that will work even if many Threads are executing it simultaneously. A piece of code is thread-safe if it only manipulates shared data structures in a manner that guarantees safe …

Different Ways to Split a String in Java

Learn to split a String with delimiters in Java using String.split(), StringUtils.split() and Splitter.split() APIs with examples.

Java Fork/Join Framework Tutorial

Java fork-Join breaks the task at hand into subtasks until the subtasks are simple enough that they can be solved without further breakups.

Difference between Java.exe and Javaw.exe

The “java.exe” and “javaw.exe” are Java executables on the Windows platform used to launch the GUI and Text-based Java programs.

Java – Calculate Age from Date of Birth

Java program to calculate age from date of birth using Java 8 localdate, period class, joda library and Java date, calendar classes.

Throttling Task Submission Rate in Java

1. Introduction In BlockingQueue and ThreadPoolExecutor example, we learned creating a CustomThreadPoolExecutor which had the following capabilities: Tasks are being submitted to the blocking queue. An executor picks up the task from the queue and execute them. It had overridden beforeExecute() and afterExecute() methods to perform pre-and-post activities if needed. …

Delete a Directory Recursively in Java

Learn to use classes from Java IO, New IO and Commons IO to delete a directory including all the subdirectories and files in it.

[Solved] java.lang.IllegalArgumentException: taglib definition not consistent with specification version

If you are working on a web application and you define the taglibs in your web.xml file then you may encounter this exception. The exception trace in server console looks like this when you start up the server. Solution You just need to confirm the allowed tags by web.xml confirming …

Java Stream API: Real-world Examples for Beginners

Java Streams can be defined as a sequence of elements from a source that supports aggregate operations on them. The source refers to a collection or array.

Functional Interfaces in Java

Introduced in Java 8, a functional interface is simply an interface that has exactly one abstract method. Learn more about functional interfaces in this tutorial.

Java Standard IO vs New IO

Java New input/output (NIO) was introduced with JDK 1.4. Picking up where Standard IO leaves, NIO provides high-speed, block-oriented IO to Java library. By defining classes to hold data, and by processing that data in blocks, NIO takes advantage of low-level optimizations in a way that the java.io package could …

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