Java Constructor Rules

The following rules must be adhered to when creating Java constructors:

1) The name of the constructor must be the same as the class name for which the constructor is being defined.
2) The constructor must not define a return type.
3) If a constructor is not defined for a class, the compiler creates a default constructor. This default constructor contains no arguments.
4) If a constructor is defined for class, the compiler does not create a default constructor.
5) Overloaded constructors may be created but there cannot be two constructors in the same class with the same argument list.

Add Additional Parameters to an ExtJS Tree Node Click

I recently encountered a situation in which I needed to send additional, dynamic parameters to a URL when an ExtJS tree node was clicked. After some trial and error, I discovered that I needed to add a TreeLoader object to my tree. (I was previously trying to use the dataUrl property of the tree itself.)

I had some parameters that were the same for each node. These I defined in the TreeLoader’s baseParams config.

The dynamic parameters I had to handle differently, since I wouldn’t know what they were until the tree node was actually clicked. To capture this click event, I defined the “beforenodeclick” event of the TreeLoader. Then, within this event, I retrieved individual attributes that had been defined for the node (in my case via a JSON packet) and added these to the TreeLoader’s baseParam config.

Example:

What is a Java Constructor?

In Java, a constructor defines the code that is run when a new object is created.

To create a constructor, define a block of code with the same name as the class. For example, the following defines the construtor for a class called “Painting”.

To invoke a constructor, use the “new” keyword, followed by the name of the class.

When creating a Java constructor, remember the Java Constructor Rules.

How to Get the Web Application Root in a JSP

To get the web application root in a Java Server Page (JSP), use the getRealPath method of the application class, as demonstrated in the example below:

How to Install jQuery

Go to http://docs.jquery.com/Downloading_jQuery

Scroll down to the “Current Version” section.

Right-click on “Uncompressed” and select “Save Link As…”

Save the file to your local web root (somewhere like C:\wwwroot\js\)

Now that the file is downloaded, jQuery is ready to be included in your website. Include it with the standard script tag, then check for the existence of jQuery, as shown in the example below:

ExtJS Expand Tree Node Listener

The listener for expanding a node in ExtJS is “expandnode”. This can be added to the “listeners” config of an ExtJS tree. Any code added to the expandnode section will run whenever a node is expanded in the tree. See example below.

How to Show and Hide an ExtJS Tree Node

Reference the example below for the syntax to show and hide an ExtJS tree node:

Note that “tree” is a variable reference to an ExtJS tree and “nodeID” is a node within that tree.