Geek2Nerd

Java Gotchas: Instance Variables Hiding | JAVA Developer's Journal

2010-06-16T10:42:00.000-07:00

Java Gotchas: Instance Variables Hiding | JAVA Developer's Journal

How to remove flex builder licence from windows xp machine ?

2009-12-22T07:32:00.000-08:00

I recently ran into a license key issue with Flex Builder and wanted to share my resolution to the problem.

In a nutshell, I accidentally got the Standard version instead of Pro. I had already entered the license key for Standard and when I went to enter the key for Pro, it balked since it was expecting a Flex 3 Standard to Flex 3 Pro license key, but the one I purchased was for Flex 3 Pro.

I simply wanted to get back to the dialog where I could enter the new Flex 3 Pro key.

I figured out that I could resolve my problem by first clearing the license # from my license.properties file at:

Windows: %ALLUSERSPROFILE%\Application Data\Adobe\Flex\license.properties
Mac: /Library/Application Support/Adobe/Flex/license.properties

I then restarted Flex Builder and was able to enter my new license information successfully.

Bug in Eclipse 3.3 with WTP 2.0.x

2009-12-22T07:27:00.000-08:00

I had just got the flex builder 3.0 licence. So I am trying to install Flex builder as Eclipse plugin (because if I install Flex builder as eclipse plugin then I can work on java project as well as flex project). Since Flex Builder 3.0 works on Eclipse 3.2 or 3.3 only, I had choosen Eclipse 3.3 (more is better :)). My Eclipse 3.3 contains WTP plugin also (WTP 2.0.2). Once I completed Flex Builder installation I had created Dynamic web project which can deploy as war (without EAR support). I had created a server with JBoss 4.2.x mappings. Previously in Eclipse 3.5 my war was successfully deployed on JBoss 4.2.x server. But in Eclipse 3.3 when I am trying to deploy same war file then it is giving deployement error like "NullPointerException "Could not publish to Server" from Eclipse". After googleing for few hours I had found there is bug in Eclipse 3.3(Europa) with WTP 2.0.x.

https://bugs.eclipse.org/bugs/show_bug.cgi?id=219627

So simple solution to this problem is try to deploy your application as ear instead of war. It will work. Other solution is upgrade your WTP with 2.1.x version.

Hidden (Less used) features of java

2009-06-07T23:21:00.000-07:00

Source code URLs. E.g. here is some legal java source code:

http://google.com

(Yes, it was in Java Puzzlers. I laughed...)

"const" is a keyword, but you can't use it.

int const = 1; // "not a statement"

const int i = 1; // "illegal start of expression"

I guess the compiler writers thought it might be used in the future and they'd better keep it reserved.

The value of:

new URL("http://www.yahoo.com").equals(new URL("http://209.191.93.52"))

is true.

Instances of the same class can access private members of other instances:

class Thing {

private int x;

public int addThings(Thing t2) {

return this.x + t2.x; // Can access t2's private value!

}

I was surprised by instance initializers the other day:

public class Foo {

public Foo() { System.out.println("constructor called"); }

static { System.out.println("static initializer called"); }

{ System.out.println("instance initializer called"); }

}

Executing the following code

new Foo();

will display:

static initializer called

instance initializer called

constructor called

instance initializer called

constructor called

I guess these would be useful if you had multiple constructors and needed common code?

Transfer of control in a finally block throws away any exception. The following code does not throw RuntimeException -- it is lost.

public static void doSomething() {

try { //Normally you would have code that doesn't explicitly appear //to throw exceptions so it would be harder to see the problem.

throw new RuntimeException();

} finally {

return;

}

From http://jamesjava.blogspot.com/2006/03/dont-return-in-finally-clause.html

A couple of people have posted about instance initializers, here's a good use for it:

Map map = new HashMap() {{

put("a key", "a value");

put("another key", "another value");

}};

Is a quick way to initialize maps if you're just doing something quick and simple.

Or using it to create a quick swing frame prototype:

JFrame frame = new JFrame();

JPanel panel = new JPanel();

panel.add( new JLabel("Hey there"){{

setBackground(Color.black);

setForeground( COlor.white);

}});

panel.add( new JButton("Ok"){{

addActionListener( new ActionListener(){

public void actionPerformed( ActionEvent ae ){

System.out.println("Button pushed");

}

});

}});

frame.add( panel );

Of course it can be abused:

JFrame frame = new JFrame(){{

add( new JPanel(){{

add( new JLabel("Hey there"){{

setBackground(Color.black);

setForeground( Color.white);

}});

add( new JButton("Ok"){{

addActionListener( new ActionListener(){

public void actionPerformed( ActionEvent ae ){

System.out.println("Button pushed");

}

});

}});

}};

This is not exactly "hidden features" and not very useful, but can be extremely interesting in some cases:

Class sun.misc.Unsafe - will allow you to implement direct memory management in Java (you can even write self-modifying Java code with this if you try a lot):

public class UnsafeUtil {

public static Unsafe unsafe;

private static long fieldOffset;

private static UnsafeUtil instance = new UnsafeUtil();

private Object obj;

static {

try {

Field f = Unsafe.class.getDeclaredField("theUnsafe");

f.setAccessible(true);

unsafe = (Unsafe)f.get(null);

fieldOffset = unsafe.objectFieldOffset(UnsafeUtil.class.getDeclaredField("obj"));

} catch (Exception e) {

throw new RuntimeException(e);

}

};

}

You can declare a class in a method:

public Foo foo(String in) {

class FooFormat extends Format {

public Object parse(String s, ParsePosition pp) { // parse stuff }

}

return (Foo) new FooFormat().parse(in);

}

2008-12-24T00:57:00.000-08:00

I became google addict now. Using iGoogle, Google Calendar, Google Docs and newly entrant Google SMS Channel. We are becoming technology slave.

Some more books

2008-11-21T04:43:00.000-08:00

Google Guice Book

Wicket in Action

Good Books

2008-11-04T05:52:00.000-08:00

Java :

Java Secrets

Excellent Sql Book:

Sql Puzzles

Web Based GroovyShell

2008-07-30T06:51:00.000-07:00

My affection to groovy leads to my first contribution towards groovy.

Web Based Groovy Shell