#static code blocks in AS3.

Introduction

Java developers have static initialization blocks, C# developers have static constructors, simply put it allow you to initialize code when your class is loaded.

Details

Flex use this principle in the Automation Framework classes, see About the automation APIs.

The Flex doc call that a delegate class and is very specific to Flex but still can be usefull in some special cases.

see jim Cheng comment on http://adamflater.blogspot.com/2007/03/static-code-blocks.html

It's used in the Automation Framework classes mainly to register automation delegate implementations to component classes before any instances get the chance to be created. You can do a text search through the framework classes and find all the instances in the mx.automation. namespace. It's not all that interesting what they do in their init() calls, but you'll get the general idea pretty quickly.

Alternatively any class in AS3 can have static code execution

package
{
    public class Something
    {
        trace( "static execution" );
        Something.hello.push( "world" );
        Something.hello.push( "world" );
        Something.hello.push( "world" );
        
        public function Something()
        {
        trace( "ctor called" )
        trace( "Something.hello: " + Something.hello );
        }
        
        public static var hello:Array = [];
        
    }
}

the differene with Flex is using [Mixin] the init() function will be called on the 1st frame during SystemManager instanciation, and with static code execution the code will be called as soon as you import or instanciate the class but before the constructor get called.

In both case, the static block will be called only once.