Big Java Blog by szpetip

Last post

2010-07-04T15:50:00.002+02:00

Unfortunately I'm closing my blog this week. I can't spend time with posting and Chinese people write junk comments all the time.I have had ~9000 visitor from 111 country all over the world in the last two year, thanks for it!Bye,...szpetip

String puzzle

2009-07-04T19:36:00.006+02:00

A short, but interesting puzzle.QuestionWhat does the following program print:AnswerWhen you run the code, you get the answer: 2.Why?The compiler translates Unicode escapes into the characters they represent before it parses the program into tokens, such as strings literals. As you see, NetBeans IDE doesn't know it, it present the code like a string with a length() method.

NetBeans 6.5.1 generates invalid web.xml

2009-05-16T15:06:00.006+02:00

If you use NetBeans 6.5.1 and you want to add a new servlet to the project, the IDE generate an invalid web.xml file and you will be not able to deploy the application.The problemIf you try to deploy the web application into an application container, then you get an exception like this:org.apache.catalina.startup.ContextConfig applicationWebConfigSEVERE: Parse error in application web.xml file at

Solve MySQL server drops and close connections in connection pool

2009-05-15T19:00:00.003+02:00

If you get "Last packet sent to the server was XX ms ago." error in your application that want to access MySQL database or you want to know, how to create a connection pool using Tomcat server and DataSource then this is your post.Connection pooling with MySQLUsing connection pool is a good way to increase your web application speed. If you create a connection pool in your application, using a

Did you know: Static import

2009-02-03T20:19:00.003+01:00

Static Import is a very simply and unnecessary opportunity in Java.Static Import The static import construct allows unqualified access to static members without inheriting from the type containing the static members. Instead, the program imports the members, either individually:import static java.lang.Math.PI;or:import static java.lang.Math.*;Once the static members have been imported, they may

Protected Access Modifier Facts

2009-02-02T21:59:00.003+01:00

I show an interesting example to the protected access modifier.Our first file, Animal.java in package world:01. package world;02. public class Animal {03. protected int age;04. }Our second file, Animal.java in package africa:01. package africa;02. import world.Animal;03. public class Zebra extends Animal {04. public void sayAge() {05. System.out.println("My age is "+age); //Works

Some interesting facts from year 2008

2008-12-31T20:05:00.006+01:00

You, visitorsI have had visitors from 73 country. This countries from Google Analytics:HungaryUnited StatesIndiaUnited KingdomFranceGermanyCanadaAustraliaItalyNetherlandsPolandSingaporeSwedenRussiaPhilippinesVenezuelaIsraelTurkeySwitzerlandSpainMexicoNorwayIndonesiaIrelandBelgiumPortugalDenmarkHondurasBrazilGreeceThailandSouth KoreaSouth AfricaArgentinaCzech

Show Image In JTable

2008-11-28T14:23:00.002+01:00

In this short post I present, how can we put and show images in JTable component.ProblemSometimes we need to put and show images in JTable. A typical situation is when we have a boolean true or false and we don't want to write true/false or yes/no captions.SolutionThe solution is very simply. We have to override thegetColumnClass(int columnIndex)method of TableModel class, like this:

Solve IllegalStateException: Illegal to call this method from injected, managed EntityManager

2008-11-25T11:05:00.003+01:00

ProblemIf we injected an EntityManager into our SessionBean and call the entityManager.getTransaction().begin() method thenIllegalStateException: Illegal to call this method from injected, managed EntityManagerexception is threw.Java Enterprise version: JEE5Used server: JBOSS 5.0.0.RC1EJB version: EJB3Why did this problem occur?We wanted to use User-managed transaction, but this is not supported

Big Java Blog is continued

2008-10-25T08:28:00.003+02:00

Dear Visitors,unfortunately I did not have time and energy to write posts in the last weeks. Now I make a promise, I return to blogging.The puzzles, the SCJP Exams and Spring themes will be continued and I try present much more interesting Java technologies.

Load jar files and Java classes dynamically

2008-08-29T19:54:00.014+02:00

In this post I present a way to load jar files and Java classes dynamically from java code. It can be very useful, if you want to create module, for example.Design PatternThe solution build up from three part, theLoader - loads and uses the jar files and Java class dynamically,Communication interface(s) - defines the interface, what can be used to communicate the program and the dynamic library,

Spring Framework - XML configuration file - Part I

2008-08-02T12:07:00.009+02:00

In this post the Spring framework's XML configuration file is presented. This files are the heart of Spring framework. Understand using these files is very important to understand Spring framework itself.Part I - This part of post is about the XML scheme, the root element, the tags inside the root element and the properties of the tag.XML SchemeTo use the XML file with Spring framework,

Spring Framework - First Steps

2008-08-02T12:00:00.001+02:00

This post teaches you some useful basic information and function of Spring framework. Writing XML configuration files, wiring beans, loading XMLs, using ApplicationContext. Creating, publishing and listening events are discussed in this post too.TaskbarNotifier example applicationThe functions above are represented through an example application. This application has a GUI frame, where we can

SCJP Exam - Objective 1.3 Part II

2008-07-13T08:02:00.006+02:00

Develop code that declares, initializes, and uses primitives, arrays, enums, and objects as static, instance, and local variables. Also, use legal identifiers for variable names.Arrays are objects in Java that store multiple variables of the same type. Arrays can hold either primitives or object references, but the array itself will always be an object on the heap, even if the array is declared

Spring Framework - Introduction

2008-07-10T19:57:00.009+02:00

Spring is an open-source framework, created by Rod Johnson. It was created to address the complexity of enterprise application development. Spring makes it possible to use JavaBeans to achieve things that were previously only possible with EJBs. However, Spring’s usefulness isn’t limited to server-side development. Any Java application can benefit from Spring in terms of simplicity, testability,

Applying Model Viewing Controller to Java Web Applications Using JSP and Servlet

2008-07-08T12:22:00.008+02:00

Model viewing controller is an architectural pattern. We can use to separate the user interface and the business logic. By decoupling models and views, MVC helps to reduce the complexity in architectural design, and to increase flexibility and reuse.It isn't goal of this post to explain the using JSP and Servlet technologies. Maybe in another post I will do it.Participants of the Model Viewing

SCJP Exam - Objective 1.3 Part I

2008-07-04T09:36:00.012+02:00

Develop code that declares, initializes, and uses primitives, arrays, enums, and objects as static, instance, and local variables. Also, use legal identifiers for variable names.Legal identifiersTechnically, legal identifiers must be composed of only Unicode characters, numbers, currency symbols, and connecting characters (like underscores).Identifiers must start with a letter, a currency

SCJP Exam - Objective 1.2

2008-07-01T16:39:00.011+02:00

Develop code that declares an interface. Develop code that implements or extends one or more interfaces. Develop code that declares an abstract class. Develop code that extends an abstract class.Interface declarationThis is discussed in Objective 1.1 - Interface declaration.Do not forget, what is in the Objective 1.1 written about interface declarations.Extend an interface an interface can extend

Java Puzzles

2008-06-29T16:40:00.003+02:00

Puzzle 1Given the following code:public class Puzzle 1 {public static void main(String[] args) {boolean b = false;System.out.println("Output - " + ( b ? 1.66 : 2 )); }}What is the output?If you think, the output is "Output - 2" then you're wrong.The right output is "Output - 2.0" because 1.66 is double, 2 is int so 2 is converted to double.Puzzle 2Given the following code:public class Puzzle2 {

SCJP Exam - Objective 1.1

2008-06-29T15:00:00.011+02:00

Develop code that declares classes (including abstract and all forms of nested classes), interfaces, and enums, and includes the appropriate use of package and import statements (including static imports).Java Source FileSample Java source file:You can download source code here.If the class is part of a package, the package statement must be the first in the source code file.The import statements

SCJP Exam - Introduction

2008-06-27T12:49:00.013+02:00

Sun Certified Programmer for the Java Platform, Standard Edition 6 (CX-310-065)As I promised, I begin my series about the Sun Certified Java Programmer Exam. In my first post I write about the exam and the objectives. The next SCJP posts review the interesting and the dodgy part of the required knowledge to exam.Exam objectives - What should I know?Source: http://www.sun.com/training/catalog/

Pop-up Window with Return Value

2008-06-27T09:50:00.006+02:00

TrickIn this post a trick is presented: possibility to return object from a pop-up dialog.It can be useful toselect and return an element of list from a pop-up dialogcreate a new object in a pop-up dialog and return itedit an object in a pop-up dialog and return itParticipantsCaller - the place, where the pop-up window is opened and the returned data is processed.Dialog - this is the pop-up

Java Inner Class Expert

2008-06-25T19:45:00.009+02:00

Puzzle 1Given the following code:1. class MyOuter {2. private int x = 7;3. class MyInner {4. public void seeOuter() {5. System.out.println("Outer x is " + x);6. }7. }8. }What is happening when we try compile the code?If you think, the output is Compilation fails then you're wrong. Line 5 looks interesting, because a private member is accessed from an inner class.Is it possible?Yes, it is.

Java Keywords or Not?

2008-06-24T12:19:00.004+02:00

PuzzleThe question is that, are thenulltruefalsewords keywords in Java or not?The answer is:no, there are not.The null, true and false words are literals, not keywords in Java.

Java Wrapper Classes, Autoboxing

2008-06-24T11:48:00.006+02:00

Puzzle 1Given the following code:...Integer i = new Integer( 1 );System.out.println( ++i );...What is the output?The output is:2This is surprising: How is it possible use ++ operator to objects? The answer is the autoboxing, what is available java 5 and above.What's happening in theSystem.out.println( ++i );line?Java unboxes, increments, reboxes the variable i, this is a good sample to

Mediator Design Patter

2008-06-23T14:00:00.024+02:00

I present this post an useful adaptation of Mediator Design Pattern. We need often create GUI forms and of course we want to process the information given by users.Participants of Mediator Design Patter (based on Wikipedia)Mediator - defines the interface for communication between Colleague objects.ConcreteMediator - implements the Mediator interface and coordinates communication between

Java Primitives Expert

2008-06-21T10:28:00.022+02:00

Puzzle 1Given the following code:1. public class Example1 {2. public static void main(String[] args) {3. byte b = 1;4. b = b + 1;5. System.out.println("b: " + b );6. }7. }What is the result?The result is: Compilation fails.Why?The problem is in the line 4: possible loss of precision.Decimal literals are implicit integers. So the type