Java Just In Time compiler-JIT compiler

In Java you have to write and compile a program only once. The Java on any platform will interpret the compiled bytecode into instructions understandable by the particular processor. However java virtual machine handles only one bytecode instruction at a time that makes execution slow. But Using the Java just-in-time compiler at the particular system platform compiles the bytecode into the particular system code. After the code has been (re-)compiled by the JIT compiler, it will usually run more quickly on the computer.
The just-in-time compiler comes with JVM and is used optionally. It compiles the bytecode into platform-specific executable code that is immediately executed. JIT compiler option should be used especially if the method executable is repeatedly reused in the code.

core skills needed by all software developers are:

The core skills needed by all software developers are:

Core Skill	Description
Read Code	The ability to understand an existing code base in order to analyze its behavior and make fixes or enhancements to it.
Write Code	This does not include any significant amount of design – just the basics of coding. An example is being able to write a method given the desired behavior (inputs, outputs, pre-conditions and post-conditions).
Design Software	The ability to determine what code is necessary to achieve some specified functionality, particularly the higher-level structure or organization of the code.
Awareness of the Software Development Life Cycle	This is an awareness of the 'big picture' of software development beyond just writing code - how the other life cycle stages (requirements, design, testing, and maintenance) impact coding and vice-versa. This includes an understanding of the types of methodologies (e.g. Agile or Waterfall) that can be used to progress through this cycle.
Use of Libraries and Frameworks	This skill could also be called "Reuse Existing Code". This skill includes the ability to search for and evaluate libraries and frameworks based on how effectively they meet your needs and the ability to integrate the chosen package into the software you are writing.
Debugging	The ability to analyze the behavior of code to diagnose a problem and find the underlying cause. This includes but is not limited to using a debugger.
Use of Integrated Development Environments	The ability to effectively use modern IDEs and an understanding of their strengths and weaknesses.
Use of Version Control	This skill includes basic use of a version control tool as well as a general understanding of software configuration management.
Automated Unit Testing	This is the ability to unit test code by writing automated tests.
Refactoring	The ability to revise existing code without impacting its functional behavior.
Use of Build Automation	This goes beyond simply writing a build script to include other related automation like continuous integration, automated deployments, and static code analysis tools.

Confirm Password Validation Using JavaScript

Password Validation Using Java Script

Collection Framework:List of classess and Interfaces

How many ways we can set java class path

How to set Java classpath? List as many ways as you can. This can be an interesting Java job interview question. Here are what I came up with:

1. Use -classpath JVM option:
   

   java -classpath C:\hello\build\classes com.javahowto.test.HelloWorld

2. Use -cp JVM option, a short form of -classpath:
   

   java -cp C:\hello\build\classes com.javahowto.test.HelloWorld

3. Use -Djava.class.path system property:
   

   java -Djava.class.path=C:\hello\build\classes com.javahowto.test.HelloWorld

4. Use CLASSPATH environment variable:
   

   set CLASSPATH=C:\hello\build\classes;
   java com.javahowto.test.HelloWorld

5. Use current directory as the default classpath:
   

   cd C:\hello\build\classes;
   java com.javahowto.test.HelloWorld

6. Package all classes into a self-containing jar file that has this in its META-INF/MANIFEST.MF.
   Main-Class: com.javahowto.test.HelloWorld
   

   java -jar hello-world.jar

   Note: when you run java with -jar option, any -classpath, or -cp options are ignored, as JVM thinks all classes are already contained inside the jar file.

Among all those options, I usually use option 1, and occasionally 6. I don't like my Java apps have dependency on environment settings like CLASSPATH, which is totally unpredictable. Using current directory as the default classpath is not a good idea either, since your classes may be scattered in several directories, folders and jar files.

Can I set classpath at java runtime dynamically and programmatically? No. Although you can set the system property java.class.path in your application, but its new value doesn't affect the system classloader. If you need to reset classpath, it's time to consider using a custom classloader as the child loader of the system classloader.

With a custom classloader, you have full control where to load class files, from local file system, remote url, or even database. Classes loaded by such a custom loader are only visible by this loader and its child loaders, but not to its parent loader nor the system classloader.

For the same reason, you can't dynamically set minimum/maximum heap size of a JVM. These JVM options are all set once when JVM is started and unchanged throughout its life.

JDK 6 now support * in classpath, so you can include all jar files in a directory to the classpath easily. But you may run into problems described in http://javahowto.blogspot.com/2006/07/jdk-6-supports-in-classpath-but-be.html

While using Glassfish v3.1 with JSF 2.0 I ended up getting this very annoying warning. WARNING: PWC4011: Unable to set request character encoding to UTF-8 from context /, because request parameters have already been read, or ServletRequest.getReader() has already been called

This seems to be very common with a very hard to find solution on google.
Finnally after a lot of search I found this link which had the solution.


Place the following in the glassfish-web.xml of the web application.

<parameter-encoding default-charset="UTF-8"/>

<!DOCTYPE glassfish-web-app PUBLIC "-//GlassFish.org//DTD GlassFish Application Server 3.1 

Servlet 3.0//EN" "http://glassfish.org/dtds/glassfish-web-app_3_0-1.dtd">

 <glassfish-web-app error-url="">
 <parameter-encoding default-charset="UTF-8"/>

...
</glassfish-web-app>

Getting values From the url in jsf

1. activation.xhtml











Your account is successfully activated!
You will in 3 seconds be redirected to home page


Activation failed! Please enter your email address to try once again.

...




Backing Bean:


/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package com.example;

import java.util.Map;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;
import javax.faces.bean.RequestScoped;
import javax.faces.context.FacesContext;

/**
*
* @author Pujya Sri
*/
@ManagedBean
@RequestScoped
public class Activation {
private boolean valid;

public boolean isValid() {
return valid;
}

public void setValid(boolean valid) {
this.valid = valid;
}

@PostConstruct
public void init() {
Map requestMap = FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap();
String key = (String) requestMap.get("key");
System.out.println("hello from url" + key);

// Get User based on activation key.
// Delete activation key from database.
// Login user.
}
// ...
}

counting the number of times a user has visited a page in HTML 5

<script type="text/javascript">
if (localStorage.pagecount)
{
localStorage.pagecount=Number(localStorage.pagecount) +1;
}
else
{
localStorage.pagecount=1;
}
document.write("Visits "+ localStorage.pagecount + " time(s).");
</script>