Geek Explains: Java, J2EE, Oracle, Puzzles, and Problem Solving!

Why String has been made immutable in Java?

2009-11-28T21:32:00.002+05:30

Why String has been made immutable in Java?Though, performance is also a reason (assuming you are already aware of the internal String pool maintained for making sure that the same String object is used more than once without having to create/re-claim it those many times), but the main reason why String has been made immutable in Java is 'Security'. Surprised? Let's understand why.Suppose you

Memory Leak in Java? Does 'static' cause it?

2009-11-17T19:37:00.004+05:30

Does 'static' cause Memory Leak in Java?What's memory leak? In simple terms, it's unused but referenced (somehow because the programmer probably unintentionally forgot to remove the references once the use of the object was over) part of the memory. Before we start discussing if 'static' can cause memory leak in Java, let me assure you that whatever you've read about Garbage Collectors in Java,

Marker Interface in Java: what, why, uses, etc.

2009-10-29T19:33:00.005+05:30

What are Marker Interfaces in Java?An empty interface having no methods or fields/constants is called a marker interface or a tag interface. This of course means if the interface is extending other interfaces (directly or indirectly) then the super interfaces must not have any inheritable member (method or field/constant) as otherwise the definition of the marker interface (an entirely empty

Connecting to an HTTP Web Service from VBA via Proxy

2009-10-13T16:40:00.004+05:30

Connecting to an HTTP Web Service from VBA Excel via a Proxy ServerThough MSDN suggests using stubs generated from the WSDL by MS Soap Toolkit for connecting to an HTTP Web Service from within VBA Excel, but it might not work as you would like it to, especially for a SOA-compliant web service and particularly in the cases where you need to access the service via a Proxy Server.I have used the

Why wait(),notify() and notifyAll() in the Object class?

2009-10-11T10:16:00.003+05:30

Why wait(), notify() and notifyAll() methods have been defined in the Object class?Java concurrency model uses locks to implement mutually exclusive access to objects in a multi-threaded environment and locks are associated with every object in Java (of type 'Object'), not only with Threads.wait, notify/notifyAll methods are used by threads to communicate with each other while trying to access a

per-thread Singleton and per-thread Logging in Java

2009-08-03T21:47:00.003+05:30

Usage of ThreadLocal: per-thread Singleton and per-thread LoggingShould you require a refresh of what ThreadLocals in Java are and how they work, refer to this article first. You can then proceed with the current article for understanding two of the most common uses of ThreadLocals in Java.per-thread Singleton impl using ThreadLocalSuppose you have a need of having a JDBC Connection objects per

Choosing the Most Specific Method - Tricky Overloading

2009-06-18T20:41:00.005+05:30

Choosing the Most Specific Method - Tricky Method OverloadingLet's start with looking at a code-segment and try to think of the output/error, it would produce when compiled/executed and subsequently we'll discuss the behavior of code.public class NullTest { public static void method(Object obj){ System.out.println("method with param type - Object"); } public static void method(String

Initializer Blocks & their alternatives in Java

2009-06-11T22:43:00.007+05:30

Initializer Blocks in Java and their possible alternativesInitializer Blocks - what are they, why & how are they used?These blocks are similar to the static initialization blocks with the only difference being the absence of the 'static' keyword. The Java compiler copies all the initializer blocks in the same order as they are in the source code in every constructor before any executable

Static Initialization Blocks & their alternatives

2009-06-07T00:27:00.005+05:30

Static Initialization Blocks and their alternatives in JavaWhy do we need Static Initialization Blocks?The easiest way of initializing fields (static or instance) in Java at the time of their declaration is simply by providing a compile time constant value of a compatible data type. For example:public class InitializationWithConstants{public static int staticIntField = 100;private boolean

Choosing a suitable access control modifier in Java

2009-05-30T20:18:00.006+05:30

How to choose a suitable access control specifier of a method or a field?Access Control Modifiers available for classes and members in JavaTop-level classes in Java can have only two access control modifiers - public and default (package-private) whereas the members have four access control modifiers - public, protected, default (package-private), and private. Nested Classes are treated as

Finding caller of an instance or static method in Java

2009-05-29T00:47:00.010+05:30

Finding Caller object, method/class of an instance method in JavaYou might think if we would ever need it? Well... you may never, but no harm in exploring whether we have any/some ways of finding this in Java or not. This question was asked by one of our visitors - Marco Servetto. Thanks Marco for bringing this question up.For instance methods, by caller you might mean either the object instance

Passing '\n' (new-line) on command line in Java

2009-05-24T17:24:00.003+05:30

Can we pass a new-line ('\n') character or any other escape sequence via command line in Java?One of our visitors (Vivek Athalye) asked this in response to the article - Tricky use of static initializer block. Thought of posting the answer as a separate article to increase the chances of it reaching to a wider range of audience.The answer to the query is NO. The question arises, if you pass the

Tricky use of static initializer in Java - Override println

2009-05-10T03:12:00.007+05:30

Can we get a different output without changing the main-method definition?public class HelloMain {/*** @param args*/public static void main(String[] args) { System.out.println("Mr. main.");}}Can we have the output of the above code-segment as "Hi, Mr. main. Bye!" without changing the main-method code?Yeah, we can have the required output by using 'static initializer' blocks effectively. As we

Finding if a number is a power of 2 or not in Java?

2009-05-03T12:53:00.004+05:30

How to find whether a number is a power of 2 or not in Java?There can be many possible solutions to this problem, but probably the most efficient remains to be the one which uses bit-level manipulation wisely.We'll talk about only that solution here and since it involves bit-level manipulation of binary sequences, so should you require a refresh, first go through this article - 2's complement, 1'

Binary rep of negative numbers in Java - 2's complement

2009-05-03T12:36:00.005+05:30

2's Complement: Binary representation of negative numbers in JavaNegative numbers in Java are represented using 2's complement. As we know that integers in Java occupy 4 bytes so to understand how a negative integer (say -4) is represented internally in Java, we first need to find the binary equivalent of the positive value of the integer (in this case 4) and subsequently by finding the 2's

Puzzle: Circular Table, Pile of Quarters and 2 Players

2009-05-02T15:25:00.003+05:30

Puzzle: There is a huge pile of quarters and a circular table. There are two people to play a game of placing the quarters down on the table alternately without any overlap. The one who can't put down a quarter loses. Assuming that the pile of quarters is non-exhaustive what will be your winning strategy? Whether you would like to start or let your partner start?Solution: The winning strategy

Viewing/Editing PPT, Doc, TIFF, etc. in your browser

2009-05-02T15:12:00.005+05:30

Viewing/Editing files without having the required s/w or tools installedWonder what will you do in case you end up getting caught in a situation where none of the widely used tools/softwares (such as MS Office, Flash, File Viewers/Editors like Acrobat, etc.) are installed on a machine on which you need to at least view (or maybe edit if possible) some docs/files?Well... until recently it was

Implementation of SAX Parser in Java using SAX2 APIs

2009-04-04T00:46:00.020+05:30

For those who have reached to this article directly, before we move on to discussing the implmenetation of a sample SAX-based XML parser in Java, they may like to refresh their understanding of SAX by referring to this article - Evolution of Java and XML combo. SAX, DOM, JAXP, JDOM >>Implementation of a SAX2-based XML parser in JavaWe will start with looking at the various steps involved in

SAX v/s DOM. How to choose between DOM and SAX?

2009-04-01T00:23:00.006+05:30

Differences between DOM and SAX. When to use what? Before going through the differences, if you need a refresh of what SAX and DOM are, please refer to this article - SAX, DOM, JAXP, & JDOM >>.While comparing two entities, we tend to see both of them as competitors and consequently comparing them to find a winner. This of course is not applicable in every case - not at least in the case of SAX

Sax, DOM, JAXP, & JDOM. Evolution of Java-XML combo.

2009-04-01T00:10:00.005+05:30

Evolution of the XML Parsing/Manipulation using JavaThe combination of Java and XML has been one of the most attracting things which had happened in the field of software development in the 21st century. It has been mainly for two reasons - Java, arguably the most widely used programming language and XML, almost unarguably the best mechanism of data description and transfer.Since these two were

Getting Class name in a static method in Java

2009-03-22T22:44:00.005+05:30

Finding the name of a Class in Java from within a static methodOne of our regular visitors (Ranvijay) had asked it a couple of days back. Though, the code is pretty straightforward, I think it might help few others if posted as an article.One of the many possible ways of finding the name of the class in Java from within a static method is by using a static nested class, which will have a public

How to recover Shift + Deleted folders/emails in Outlook?

2009-03-02T20:27:00.008+05:30

How to recover Shift + Deleted folders/emails in Microsoft Outlook?Ever wondered if you can really recover something in Windows, which you have Shift + Deleted? Well, you can do that at least in few cases (if not in all) - one of them being recovering folders/emails which you accidentally Shift + Deleted in your Microsoft Outlook (running with MS Exchange Server). I managed to delete one

Outlook Express v/s Outlook. Which suits you better?

2009-03-02T20:09:00.005+05:30

Outlook Express v/s MS Outlook. How to choose one between the two?Outlook Express v/s Microsoft OutlookMany of you would already be aware of the main difference between the two. For those, who might not have cared to thought of it so far, here is the summary of the main difference(s) between the two messaging and collaboration clients delivered to us by Microsoft:-Outlook Express: it has been

ThreadLocal & InheritableThreadLocal in Java, initialValue() v/s set(), Uses of childValue()

2009-02-22T22:03:00.005+05:30

ThreadLocal in Java - what is it used for?As the name suggests this Java library class is used for supporting thread-local variables - the variables which are local to the particular thread instance and hence each thread will have their own copy of such variables which will be initialized every time a new thread is spawned.To be more clear, let's take one simple example. If you have a class

LoadLibrary failed - a DLL initialization routine failed

2009-02-16T23:58:00.006+05:30

Resolving 'LoadLibrary failed - a DLL initialization routine failed' errorThere might be other reasons for this error as well, but the most common one is probably because of a missing dependent DLL. While trying to register SOAPIS30.dll (for those who are new to DLL installation - that's done by using RegSvr32.exe OR Gacutil.exe), I encountered this error.Identifying the problem and fixing that -

java.lang.UnsupportedClassVersionError: why is it thrown & how to resolve?

2009-01-24T20:52:00.000+05:30

java.lang.UnsupportedClassVersionError: when is it thrown by a JVM & how to resolve it? UnsupportedClassVersionError is (evidently a descendant of the Error class in Java) which subclasses java.lang.ClassFormatError which in turn subclasses java.lang.LinkageError (which is a direct subclass of java.lang.Error). This error is thrown in the cases when the JVM (Java Virtual Machine) attempts to read

The 25 Most Dangerous Programming Errors

2009-01-16T00:08:00.002+05:30

25 Most Dangerous Programming Errors listed by CWE/SANS The US National Security Agency has helped building a list of the top 25 world's most dangerous programming errors which may lead to security vulnerabilities that can be attacked by the cyber criminals and this list of 25 errors is now assumed to be the minimum set of coding errors that must be fixed completely before letting the code to go

finally contd.: an interesting try-catch-finally scenario

2009-01-08T23:09:00.006+05:30

If not very comfortable with finally block and its execution then you may probably like to go through this article first - playing with try-catch-finally in Java >>. It covers some pretty interesting scenarios covering various possible scenarios of try, catch, and finally blocks followed by the precise explanation of their execution in each of these scenarios. Come back to this article once you

XML Schema and its anatomy, Uses of XSDs, Namespaces

2009-01-02T23:53:00.004+05:30

XML Schema and its anatomy, Applications of XML Schemas, NamespacesXML Schema was approved as an official recommendation by the WOrld Wide Web Consortium (W3C) in 2001. W3C defines XML Schema as "XML Schemas express shared vocabularies and allow machines to carry out rules made by people. They provide a means for defining the structure, content, and semantics of XML documents."As it's clear from

www v/s www1 v/s www2. Role of CNAME and DNS.

2008-12-26T11:59:00.007+05:30

How are www, www1, www2, etc. different? Role of CNAME & DNS?Let's start with discussing what the different parts of a typical web site address mean? Say for example, if we take http://www.google.com then the first part from left http denotes the protocol being used for communication on Internet. The two most popular protocols being used are http and ftp. Requests using different protocols

How does Password Encryption work in real world?

2008-12-22T00:02:00.008+05:30

Password encryption in work: illustration using SBI Sign In processLast week I received an email (from one of our visitors, Anil) inquiring about what all actually takes place to ensure that the password (or any other sensitive data for that matter) gets encrypted before the request is sent to the Web/App Server? Thanks Anil for raising such a nice point.In this article, I'll try to discuss how

Pictorial rep of Client-side password encryption

2008-12-21T23:41:00.013+05:30

This article is a part #2 of the article 'How does Password Encryption work in real world?'. If you have landed directly on this article then you would probably like to go through the first part of the article - Complete working of Password Encryption >>Diagrammatic rep of how password encryption works for SBI Net Banking#1: typing the Login URL of Online SBI will get you a web page which will

Constructor Injection: how it works? Impl using Pico

2008-12-18T23:29:00.004+05:30

Implementation of Constructor Injection using Pico. How CI works?Constructor Injection is mainly used by a highly embeddable, lightweight, and full-service IoC Container named PicoContainer. Should you need to refresh your understanding of DI and its types, go through this article - Dependency Injection & its types>> Let's see how the Constructor Injection phenomenon works. We will take one

Spring: Beans, Container, Metadata, IoC Instantiation

2008-12-13T20:58:00.004+05:30

Spring fwk: Beans, Containers, Configuration Metadata, IoC InstantiationBeans - what are they and why do we call them beans?Any object in your Spring application which is instantiated, assembled, and otherwise managed by the Spring IoC Container is called a Bean. Nothing special about these objects, except that the configuration metadata of the Spring framework contains details of these objects

Spring: Inversion of Control, Dependency Injection

2008-12-09T22:46:00.006+05:30

Spring IoC - Inversion of Control. DI - Dependency Injection.Spring IoC - Inversion of ControlIoC pattern is defined as "A software design pattern and set of associated programming techniques in which the flow of control of a system is inverted in comparison to the traditional interaction mode." which means instead of the application calling the framework for services (as is the case with

Session impl of a Web App served by multiple JVMs

2008-12-06T21:46:00.005+05:30

Session implementation of a Web App spread on multiple JVMs/ServersShould you need a refreshed understanding of what HTTP Sessions are and why are they actually needed, please refer to the article - Need for Session Tracking and Session Tracking Mechanism >>All the three techniques of HTTP session maintenance namely Cookies, URL Rewriting, and Hidden Fields have quite a few limitations. Some of

Creating documents directly from emails in GMail

2008-12-06T00:53:00.005+05:30

Creating documents straight out of your emails in GMailIf you have not noticed (or used) this feature so far then probably you are missing a really nice feature of GMail Labs. The feature was introduced to the entire world at the Official GMail Blog on Dec 16, 2008.Okay, what's this used for? As the name might suggest, it's for creating documents straightaway from your emails. So, if you think

Implicit vs Explicit Cursors. Static vs Dynamic Cursors.

2008-11-29T23:57:00.002+05:30

Life Cycle of DB Cursors. Implicit vs Explicit, Static vs Dynamic Cursors.What are Database Cursors?Oracle RDBMS assigns a private area to contain related information and the data returned or affected by a SQL statement when executed from a PL/SQL block. A Cursor is a mechanism of naming that private area so that the contents of which can be manipulated programmatically.A Cursor in its simplest

AspectJ, Aspect-Oriented Programming, Spring AOP

2008-11-23T09:03:00.005+05:30

Aspect, AOP, AspectJ, Spring AOP, AspectJ vs Spring AOPWhat's an Aspect? What's Aspect-Oriented Programming (AOP)?An Aspect can be understood as a crosscutting concern which can not be covered by the usual grouping and abstraction mechanisms supported by the various programming methodologies. Why is that so? Because many concerns can cut across multiple abstractions as defined by the underlying

Using XSD to create XML Doc and applying an XSL on it

2008-11-20T22:41:00.007+05:30

Using XSD to create XML Doc and applying an XSL on itI was given an XSD (XML Schema) and was asked to do a couple of things:- (i) Generate an XML document out of the XSD and (ii) Generate (and test of course) an XSL to check if one of the XML elements (named 'filename') contained a specific string (say "abc") at a specific position or not. These tasks are of course not very complex in nature, but

Ease of Dev in Java 5: Generics, Autoboxing, Static Import, Enhanced for, Annotation, & Typesafe enum

2008-11-16T01:57:00.004+05:30

Java 5 features for easier dev: Generics, Autoboxing/Unboxing, Static Import, Enhanced for, Typesafe enums, Annotaion/MetadataI had to give a presentation on Java 5.0 few weeks back in my company and during that time I went through an interesting interview (taken sometime in 2003) of Joshua Bloch who touch based on the six popular new features of Java 2 Platform, Standard Edition 5.0 (also knwon

Playing with try-catch-finally in Java. Intersting scenarios.

2008-11-12T23:04:00.004+05:30

Various possible scenarios for try-catch-finally blocks and their executionDo you feel that you understand how try-catch and finally blocks are executed in Java? If no then you would first like to read the article - finally explained >>So now I can safely assume that you have a fair understanding of how the exception handling mechanism actually works in Java. Okay, let's try that out with few

Image Processing in Java. Dim, Regions, Thumbnails, etc.

2008-11-11T23:03:00.006+05:30

Using Java APIs for getting dim, selecting region, thumbnails, etc..The Java 2D API treats all the images as a rectangular 2D array of pixels, where a pixel is nothing but the representation of the color at that position in the image and evidently dimension is the horizontal (width) and vertical (height) extent of the image.The API uses representation of images as objects of the class

MVC Pattern & its importance. Push & Pull Mechanism

2008-11-08T22:36:00.002+05:30

MVC Pattern & its importance. Push & Pull MechanismMVC (Model View Controller) architecture/patternIt's an architecture (which is sometimes referred to as a design pattern as well) pattern which clearly separates the Business Logic, Presentation of the Response, and the Request Handling & Processing. JSP Model 2 Architecture is based on the MVC pattern.Does it sound complex? Well... it's not. In

Creating Windows NT Services for a Java application

2008-11-02T01:01:00.001+05:30

Creating Windows NT Services out of a Java applicationThere are many ways of creating Windows Services out of Java Applications, one very popular of them is by using the Java Service Wrapper (a set of batch files) developed by Tanuki Software. Below are the steps which one need to follow to install, launch, stop, or uninstall Windows NT services for a Java app:-Download the utilitywrapper.exe is

Web Vulnerability Detection: SQL Injection, XSS, GHDB, Sniffers

2008-10-29T00:50:00.001+05:30

Web Vulnerability Detection: SQL Injection, XSS, GHDB, SniffersWhat's Web Vulnerability & how does it impact?Why the Web Sites are still vulnerable when we have technologies like Firewaals, SSL, etc.? Because most of the web sites are made for a public use and need to be available 24x7 on a publicly accessible route. Since the Web applications have access to the data in the back-end and in most

XML: what's it an how it different from HTML?

2008-10-29T00:23:00.001+05:30

XML - what's it an how it different from HTML? XML - Extensible Markup LanguageXML is a system and hardware independent language used for producing Unicode text files called XML Documents which define data and describe the structure of the contained data. The World Wide Web Consortium (also known as W3C) owns and controls the specifications of this language.Since XML Documents contain data so

ORM: Object Relational Mapping Technology, JDO, JPA, SDO

2008-10-26T00:12:00.001+05:30

ORM (Object Relational Mapping): This is a programming technique which eliminates the need of transforming the objects into scalar values while saving the objects into (and also while building the objects while retrieving) a relational database which can't directly store object values. This technique is also referred to as I/RM and O/R Mapping. Thus we see that ORM is a technique which makes

XML Database - NXD, XAPI, Apache Xindice, Ozone DB, Sedna

2008-10-22T01:02:00.001+05:30

XML Database - NXD, XAPI, Apache Xindice, Ozone DB, SednaXML Database - what's it?XML Databse is just like any other database system with the only difference being the data is stored in XML format in this case. We have two major categories of XML Databases:-XML-enabled DB: Here the underlying database is one of the traditional databases only, but the database gets equipped with the ability of

Evolution of Agile Methodologies. Engineering vs Agile.

2008-10-19T01:10:00.004+05:30

Evolution of Agile Methodologies. Engineering vs Agile Methodologies.Software Development was initially based on coding and fixing. That worked well for smaller software, but as the size and complexities of software grew a need for a proper process was felt because the debugging and testing of such software became extremely difficult. This gave birth to the Engineering Methodologies.Engineering

What is SQL Injection? How can it be handled?

2008-10-16T23:34:00.004+05:30

What is SQL Injection? How can it be handled?SQL Injection - what's it?It's an attack where some malicious piece of code is added to a SQL statement which is later passed to a DBMS to be parsed and executed. If the overall SQL statement string is syntactically correct (and of course if the user has rights to fire those SQL commands) then the SQL gets executed by the SQL Engine and consequently

CGI, Servlets, JSP, Model 1 & 2 Architectures

2008-10-12T14:54:00.005+05:30

CGI, Servlets, JSP, Model 1 & 2 ArchitecturesEvolution of Dynamic Content GenerationWhen World Wide Web (WWW) started in the year 1989 at he CERN laboratory the idea was to have a mechanism which enabled sharing of research information among researchers using hypertext docs. And hence Web was designed to serve static contents in the beginning. The obvious and natural progression was to have the

How to implement Pagination in JSP Pages?

2008-10-12T14:47:00.003+05:30

This question was asked by one of our visitors, Ranvijay. Thank you Ranvijay for posting it. I thought it's worth posting the response as a separate article to improve the chances of it reaching to a wider range of visitors.How to implement Pagination in JSP?I'm afraid there isn't a standard way of implementing pagination. Different situations may demand diffrent strategies to be followed. If you

Recursion - adv/lim, factorial, Ackemann's fun

2008-10-12T13:55:00.006+05:30

Recursion - adv/disadv, types, factorial, Ackemann's fun, etc.What is Recursion?It's a programming technique which facilitates writing simpler, shorter, and clearer code. A fucntion calling itself (either directly or indirectly) is called recursion. There are many programming situations which are very difficult (if not practically impossible) to be modelled without using recursion.Advantages of

Structural Patterns contd. - Bridge, Facade, Flyweight, Proxy Design Patterns

2008-10-02T23:04:00.005+05:30

Structural Patterns contd. - Bridge, Facade, Flyweight, ProxyIf you have directly reached to this article then you may like to first go through the first article on structural design patterns which covers what they are all about and discusses Adapter, Decorator, and Composite design patterns in particular.Bridge Design PatternThis design pattern is used to achieve the very basic purpose of Object

Structural Patterns - Adapter, Decorator, Composite, etc.

2008-09-28T01:17:00.005+05:30

Structural Design Patterns - Adapter, Decorator, Composite, etc.Want to refresh your understanding of Design Patterns, its types, usability, etc. first then you may like to refer to this article - Design Patterns >> Structural Design PatternsDesign Patterns belonging to this category are used to combine classes and objects to form larger structures to suit your requirements. How do we actually

Creating zip/jar files programmatically in Java

2008-09-22T00:12:00.004+05:30

Creating zip/jar files programmatically in JavaWrite a Java application which automatically zips the directories. The application should accept the input and output directories specified either through command prompt or via a properties file. The user should be able to specify From Date and To Date if s/he wishes so that only those directories in the specified input directory which have their

Differences between Swing and AWT. When to use what?

2008-09-21T23:59:00.005+05:30

Differences between Swing and AWT. When to use what?"Swing" was actually the code name used by Sun during the development and it was planned that on release the extension will be known as JFC (Java Foundation Classes), but Swing managed to beat JFC in popularity even after the release of the package.Swing package can be used with Java 1.1 as well. For that we need to include three JARs -

Creational Patterns contd. - Builder & Prototype

2008-09-15T23:45:00.005+05:30

Creational Patterns contd. - Builder Design Pattern & Prototype Design PatternBuilder Design Pattern - this design pattern is used for building a different set of objects based on some passed parameters. We already know that Factory Pattern also does a similar thing, so why to have a different design pattern. Well... Factory Pattern is used to return objects of different type (descendents of a

Creational Patterns - Singleton, Factory, & Abstract Fac

2008-09-08T23:04:00.003+05:30

If you're interested in refreshing your understanding of Design Patterns and their Types before moving on to the details of Creational Patterns then you may refer to this article - Design Patterns - Types & Precepts >>Creational Design PatternsAs the name suggests these design patterns are used to control the instantiation of a class. Why do we need it? Because the program should not be

Design Patterns - Types and suggested Precepts

2008-09-08T22:51:00.009+05:30

What are Design Patterns?Design Patterns are basically a catalog of common interactions between objects. These interactions have been found, tested/tried, and optimized by skilled programmers to help others in solving some of their very common programming problems in an efficient way. Design Patterns simply illustrate how objects can communicate with each other without being much concerned about

Diff java.lang.Class instances for the same Type ?

2008-08-27T20:35:00.006+05:30

One of our visitors (Priyank) asked these questions via email. Thanks Priyank for your participation.Can we have two java.lang.Class instances of the same Type?Yeah... we can have any number of java.lang.Class instances of the same type provided we get the Type loaded by a different ClassLoader instance everytime. Please note that even if we use the same ClassLoader class, but if we use different

Using Reg Ex to identify Strings representing int/float

2008-08-26T20:28:00.004+05:30

Write a Java program using RegEx to identify a String representing int/float (Whitespaces allowed)Some of you may think why to use Reg Ex to identify Strings reprenting numbers as Java has other options as including the well known Scanner class introduced in Java 5.0, but the point here is not to discuss if we really need to use Reg Ex instead the idea is to make you familiar with usage of

Java Code: Using Reg Ex to identify Strings rep of int/float

2008-08-26T20:07:00.006+05:30

Using Reg Ex to identify String representation of int/float (Whitespaces allowed)Find below a complete Java program illustrating the usage of Regular Expressions (introduced in Java 1.4) to identify String representations of int or float values. The program first tries to identify Strings representing only a valid int value without any leading, trailing or embedded whitespaces and subsequently

zip vs jar. When to use what? Which one is performant?

2008-08-18T22:07:00.003+05:30

zip vs jar. When to use what? Which one is performant?jar - the default 'jar' utility (and a file format as well. Read more about the JAR file format in this article - JAR, WAR, and EAR >>) is the Sun's implementation which has been written in Java language. This is obviously slower (though only slightly) than those 'jar' utilities which have been written using C language. 'fastjar' is an example

How many ways of creating objects in Java?

2008-08-13T21:37:00.003+05:30

How many ways of creating objects in Java?Well... there aren't many different ways I suppose. But from an application programmer perspective here are the different possible ways of creating objects in Java:-Using new operator - the most commonly used way by far. 'new' is an operator and the only operand it requires is a constructor which will be used for initializting the newly created instance.

How can we access an unreachable object in Java?

2008-08-12T21:57:00.004+05:30

Can we access an unreachable object in Java?Yeah... we can. Sounds strange? But, it's true. We can access an unreachable object in Java.This can be done by overriding the finalize() method and inside the method we can assign the reference 'this' to some other active reference and this way the unreachable object becomes reachable again which can be accessed like any other object. However this is

Generate unique primary key automatically in MySQL

2008-08-12T21:47:00.006+05:30

How to generate unique primary key automatically for every record in MySQL?Note: This question was asked by one anonymous visitor as a comment. Sharing the response as a separate article to make it more visible to our visitors.I've not used MySQL for quite a while now. When I used MySQL some 3-4 years back I probably couldn't find any direct support for Sequences in MySQL (unlike Oracle) and

WSDL - Web Services Description Language

2008-08-08T21:11:00.006+05:30

WSDL - Web Services Description LanguageYou may like to refresh your understanding of the Web Services by going through this article - Web Services - What, Why, Usage, & Shortcomings>>The WSDL (Web Services Description Language) is a grammar which uses XML for describing all the details of a Web Service which a consumer may like to have for using that Web Service. These details are:-Message

Security Model in Java and its evolution

2008-08-08T21:06:00.003+05:30

Security Model in Java and its evolutionJava was originally designed for developing Network Applications and as we know that such applications are more prone to potential attacks hence a need for the Security Model was felt as one of the most important feature of the Java architecture.Since the inception of the Java architecture, the Security Model has also evolved from the Basic Sandox to the

A sample WSDL document

2008-08-08T20:53:00.005+05:30

Guarded Block in Java - what's it & why is it used?

2008-07-31T22:27:00.004+05:30

Guarded Blocks in Java - what are they & why are they used?This is one of the most popular mechanisms of co-ordinating the execution of multiple threads in a multithreaded application. Such a block keeps checking for a particular condition to become true and only in that case the actual execution of the thread resumes.Why should a thread's execution required to be co-ordinated with that of other

Deadlock - what's it? How to deal with this situation?

2008-07-29T22:18:00.004+05:30

Deadlock - what's it? How to deal with a Deadlock situation?What's Deadlock?It's basically a situation where two or more threads are blocked forever waiting for each other to release an acquired monitor to proceed further. Let me try to explain it using an example. Suppose we have two thread - threadA and threadB. There are two objects of a class TestClass - objA and objB and we have two

Methods accepting Variable Argument Lists in Java?

2008-07-23T20:05:00.004+05:30

How to implement methods accepting Variable Argument Lists in Java?Java doesn't have a built-in feature to handle variable argument lists to a method call, the way we have in C/C++. But, there are several alternative ways of achieving this in Java using simple programming constructs. Let's try to discuss these alternative ways:-Method Overloading - it directly comes to our mind whenever we start

IEEE 754 floating point arithmetic used by Java

2008-07-23T19:52:00.002+05:30

IEEE 754 floating point arithmetic used by JavaBe careful while using floating point arithmetic in Java and don't reply on the mathematically accurate results produced by an expression involving floating point arithmetic for the simple reason that these arithmetics are not guaranteed to be exactly identical to their mathematical counterparts. The underlying reason for such a discrepancy is that

Concurrent execution of static and non-static synchronized methods

2008-07-21T21:42:00.004+05:30

Concurrent execution of static and non-static synchronized methodsWe have a scenario where we have a static synchronized method and a non-static synchronized method. As we know that a static method can only access static members of the class whereas a non-static method can access both static as well as non-static members. This liberty can put us into a situation where a non-static method might be

Composition vs Aggregation. What's Association?

2008-07-15T23:29:00.003+05:30

Composition vs Aggregation. How is Association related to them?Association - it's a structural relationship between two classifiers - classes or use cases. Cyclic association is also possible when the same entity plays two different roles and contains an association describing the relationship between the two roles.In UML notation an association is depicted by a solid line. For example: suppose

Java architecture, JRE, Java Platform, JVM, JDK

2008-07-15T23:24:00.002+05:30

Java architecture, JRE, Java Platform, JVM, JDKJava ArchitectureJava is much more than just a popular programming language instead it's a complete architecture. The entire Java archirecture can be broadly categorized into three technologies which work together to make Java a powerful software development architecture. The components of the Java architecture are:-The Java Programming Language -

Loading, Linking, & Initialization of Types in Java

2008-07-09T22:01:00.008+05:30

Loading, Linking, & Initialization of Types in JavaThe Java Virtual Machine makes the Types (we'll discuss here the user defined Types - classes and interfaces... built-in types also undergo similar set of phases and they are normally loaded as part of the JVM process start-up) available to a Java program under execution and any Type undergoes the following phases during its entire life cycle:-

Synchronization of static and instance methods in Java

2008-07-05T19:58:00.004+05:30

Synchronization of static methods/fields in JavaWhat's an Intrinsic lock OR a monitor lock in Java?An intrinsic lock, a monitor lock, or a monitor - all three refer to the same internal entity associated with every object in Java which enables the implementation of the Synchronization mechanism. This lock is used to enforce an exclusive and consistent access in Java as a monitor can be acquired

Synchronization of constructors not allowed in Java - why?

2008-07-05T19:53:00.005+05:30

Synchronization of constructors not allowed in Java - why?In Java, synchronization of contructors is not allowed (results in a compile time error) as only the thread which is constructing the object should have access to the object and hence any other thread is not granted access until the construction of the object is complete. So, no explicit synchronization needed for constructors.Caution:

What is Reentrant Synchronization in Java?

2008-07-05T19:45:00.003+05:30

What is Reentrant Synchronization in Java?We know that a thread can not acquire a monitor which is owned by another thread. A thread own a monitor for the period between the time it acquires the monitor for entering a synchronized method/block and the time when it releases the monitor when the thread either returns from the method (or completes the block) OR throws an uncaught exception.But, a

Puzzle: 2 crystal balls, 100 storey building, find no. of drops required?

2008-07-05T19:35:00.004+05:30

Puzzle: There are two identical crystal balls and one needs to find out which is the maximum floor in a 100 storey building from where the balls can fall before they break. In the most efficient way, what will be the maximum number of drops required to find the right floor in any possible scenario? The balls are allowed to be broken (if required) while finding the right floor.Solution: The

Puzzle: Deck of 52 cards, two players, who will win?

2008-07-05T19:30:00.002+05:30

Puzzle: The rules of a card game (having 52 cards) played between two peole are:- they will turn over two cards at a time. If both the cards are Black they will go the first player's pile and if both are Red they they will go to the second player's pile. If one is Red and one Black then both the cards will simply be discarded.The process of turning over two cards at a time is repeated till all

Thread.State in Java? BLOCKED vs WAITING

2008-07-03T22:27:00.003+05:30

What is Thread.State in Java? What's it used for?Thread.State - This is a static nested class (Read more about nested classes in the article - Nested Classes & Inner Classes in Java >>) of the Thread class. This is one of the additions of Java 5 and this class actually inherits the abstract class Enum which is the common base class of all Java language enumeration types i.e., Thread.State is

Ways of combining Web Services. Orchestration vs Choreography

2008-07-03T22:03:00.005+05:30

Ways of combining Web Services. Orchestration vs ChoreographyIf you want to refresh your understanding of Web Services, you may read this article - Web Services - What, How, Why, & Shortcomings >>As we know that Web Services are actually application components each of which normally performs one discrete functionality of the overall application. So, we definitely need some way of combining these

Alternatives of stop, suspend, resume of a Thread

2008-07-01T22:16:00.006+05:30

Did you go through the first part of the article which discussed - Why Thread.stop() method is deprecated in Java? Why ThreadDeath is a subclass of Error and not of Exception? Can't we catch the ThreadDeath and fix the damaged objects? What will happen if stop() method is called on a thread which is yet to start? ... You may like to go through the first part before proceeding with this part.This

Why stop, suspend, & resume of Thread are Deprecated

2008-07-01T21:39:00.006+05:30

This is a slightly longer article and hence divided into two parts. This is the first part of the article, which will try to answer the following questions:-Why Thread.stop() method is deprecated in Java?Why ThreadDeath is a subclass of Error and not of Exception?Can't we catch the ThreadDeath and fix the damaged objects?What will happen if stop() method is called on a thread which is yet to

Conditional compilation & Conditional loading of a class

2008-06-28T18:56:00.002+05:30

Conditional compilation & Conditional loading/initialization of a classHow can one conditionally compile some code in a class?It's very simple. One possible way is to use a static final boolean variable and assign that variable a value 'false' during declaration. Since it's a final variable, so the compiler knows that the value is not going to change any further. Since the variable is static, so

Asserions in Java? Assertions vs Exception? Its usage?

2008-06-28T18:44:00.003+05:30

Asserions in Java? Assertions vs Exception? Where to Use & Where NOT?Assertion in JavaAn assertion is a special statement which contains one boolean expression and if that boolean expression returns 'false' then the program throws an AssertionError which is an unchecked exception and it normally terminates the current program/application.This boolean expression is normally used to verify our

Free 2/3-column XML Skins/Templates for Blogger

2008-06-28T12:59:00.001+05:30

Free 2-column/3-column XML Skins/Templates for BloggerDownload & Apply the theme used by this blogAfter emailing the XML skin of my blog quite a few times, I thought it would be better to share it on the blog itself so that people interested in it can download it directly from here instead of requesting that via email.Credits for the XML theme that this blog usesAs you can see from the 'Credits'

Inserting AdSense Ads in Post Body, Sidebar, etc..

2008-06-28T12:17:00.001+05:30

Inserting Google AdSense Ads in Post Body, Sidebar, Footer, etc.Inserting Google AdSense Ads to Post BodyFind below few simple steps to insert Google AdSense Ads in the post body. You just need to parse your AdSense Ad code before inserting it into the template. If you don't have a HTML parser then use this Online HTML Parser.Once you have got the parsed HTML AdSense Ad code, follow the below

Do Interfaces really inherit the Object class in Java?

2008-06-25T14:19:00.005+05:30

Do Interfaces really inherit the class Object in Java (the cosmic sperclass)?Well... the answer is NO. An interface can't inherit from a class in Java, not at least directly. So, we can safely say that interfaces don't inherit from the Object class. Okay... so how can they do that indirectly? We know that interfaces can have classes declared as members as well just like they can have constants.

Error/Exception Handling in JSP - using JSPs or Servlets

2008-06-24T21:47:00.005+05:30

Error/Exception Handling in JSP - using JSPs or ServletsAn unrecoverable error while executing a JSP page can be handled by specifying the error JSP pages. These error JSP pages can either be specified in the Deployment Descriptor (web.xml) OR a JSP can have its own error page specified with the errorPage attribute of the page directive. The specifed error pages must have isErrorPage attribute of

Field Hiding in Java - fields are only hidden not overridden

2008-06-24T11:49:00.005+05:30

Field Hiding in Java - fields are only hidden not overriddenField in Java are only hidden and not actually overridden (that doesn't mean that we'll get a compilet time error while trying this, instead they are not overridden in its true sense). Overriding means the member should be invoked based on the run time type of the object and not based on the declared type. But binding for fields in Java

Automating user input for GUI programs in Java - How?

2008-06-23T22:18:00.006+05:30

How can you automate user input for GUI programs in Java?How to automate GUI programs in Java? Or, How to automate User Inputs from KeyBoard/Mouse for an AWT or Swing based GUI application?Suppose we want to create a small GUI based demo application which requires automated user input events (which we would have provided by using Keyboard/Mouse). JDK 1.3 introduced a new class named

Detecting the Shutdown of a JVM programmatically

2008-06-23T22:11:00.004+05:30

How can you detect the Shutdown of a JVM programmatically?One possible way of doing it by adding a Shudown Hook to the JVM (Is there any other way?). Of course I'm not considering the case where a new process would be launched just to kill the JVM. It should be normal JVM Shutdown - without interference of an external interrupt by any user process. OKay... so let's discuss how can we write and

Common Questions on Shutdown Hooks in Java

2008-06-23T22:00:00.003+05:30

Common Questions on Shutdown Hooks in JavaIf you like to refresh your understanding of Shutdown Hooks then read this article first - Shutdown Hooks in Java >>Question: Why doesn't Java provide infomation as to why the JVM is shutting down?Answer: Because it can not be done in a portable way. There are certain platforms which have capabilities of notifying the potential causes of a JVM shutdown

Overruling uncaught exceptions in Java - how to?

2008-06-23T21:50:00.003+05:30

Overruling uncaught exceptions in Java - how to do?An uncaught exception normally propagates until the default handler (or some other intermediate handler if found on the way) handles it. The default handler prints the detailes message with the exception name and also the stack trace before exiting the process.Is there a way to nullify the effect of an uncaught exception without handling it? Yes.

finally explained - common questions, uses, etc.

2008-06-23T21:40:00.007+05:30

finally block - is it guaranteed to run?Yeah... the finally block is always executed irrespective of whether the try block executes normally or throws an exception and also irrespetcive of whether the catch block (if found any) hanldes the exception normally or throws an exception itself. Whatever be the case, the finally block is always guaranteed to be executed i.e., if the control has entered