Monday

as3 syntax reference























































































































































































































Concept/Language Construct



Java 5.0




ActionScript 3.0



Class library packaging



.jar



.swc




Inheritance



class Employee extends Person{



class Employee extends Person{




Variable declaration and initialization



String firstName=”John”;


Date shipDate=new Date();


int i;


int a, b=10;


double salary;



var firstName:String=”John”;


var shipDate:Date=new Date();


var i:int;


var a:int, b:int=10;


var salary:Number;



Undeclared variables




n/a



It’s an equivalent to the wild card type notation *. If you declare a variable but do not specify its type, the * type will apply.


A default value: undefined


var myVar:*;




Variable scopes



block: declared within curly braces,

local: declared within a method or a block



member: declared on the class level



no global variables



No block scope: the minimal scope is a function



local: declared within a function



member: declared on the class level



If a variable is declared outside of any function or class definition, it has global scope.



Strings




Immutable, store sequences of two-byte Unicode characters



Immutable, store sequences of two-byte Unicode characters



Terminating statements with semicolons



A must




If you write one statement per line you can omit it.



Strict equality operator



n/a



===



for strict non-equality use


!==



Constant qualifier



The keyword final



final int STATE=”NY”;




The keyword const



const STATE:int =”NY”;



Type checking



Static (checked at compile time)




Dynamic (checked at run-time) and static (it’s so called ‘strict mode’, which is default in Flex Builder)



Type check operator



instanceof



is – checks data type, i.e. if (myVar is String){




The is operator is a replacement of older instanceof



The as operator



n/a



Similar to is operator, but returns not Boolean, but the result of expression:




var orderId:String=”123”;


var orderIdN:Number=orderId as Number;


trace(orderIdN);//prints 123




Primitives



byte, int, long, float, double,short, boolean, char




all primitives in ActionScript are objects.

Boolean, int, uint, Number, String



The following lines are equivalent;


var age:int = 25;


var age:int = new int(25);




Complex types



n/a



Array, Date, Error, Function, RegExp, XML, and XMLList




Array declaration and instantiation



int quarterResults[];


quarterResults =

new int[4];




int quarterResults[]={25,33,56,84};





var quarterResults:Array

=new Array();


or


var quarterResults:Array=[];



var quarterResults:Array=

[25, 33, 56, 84];


AS3 also has associative arrays that uses named elements instead of numeric indexes (similar to Hashtable).



The top class in the inheritance tree



Object




Object




Casting syntax: cast the class Object to Person:




Person p=(Person) myObject;




var p:Person= Person(myObject);


or


var p:Person= myObject as Person;



upcasting



class Xyz extends Abc{}


Abc myObj = new Xyz();




class Xyz extends Abc{}


var myObj:Abc=new Xyz();




Un-typed variable



n/a



var myObject:*


var myObject:



packages



package com.xyz;


class myClass {



package com.xyz{


class myClass{



}


ActionScript packages can include not only classes, but separate functions as well



Class access levels



public, private, protected


if none is specified, classes have package access level



public, private, protected


if none is specified, classes have internal access level (similar to package access level in Java)



Custom access levels: namespaces



n/a




Similar to XML namespaces.


namespace abc;


abc function myCalc(){}



or



abc::myCalc(){}



use namespace abc ;





Console output



System.out.println();



// in debug mode only


trace();





imports



import com.abc.*;


import com.abc.MyClass;



import com.abc.*;



import com.abc.MyClass;



packages must be imported even if the class names are fully qualified in the code.



Unordered key-value pairs



Hashtable, Map



Hashtable friends = new Hashtable();




friends.put(“good”,

“Mary”);


friends.put(“best”,

“Bill”);


friends.put(“bad”,

“Masha”);



String bestFriend= friends.get(“best”);


// bestFriend is Bill




Associative Arrays



Allows referencing its elements by names instead of indexes.


var friends:Array=new Array();

friends["good"]=”Mary”;


friends["best"]=”Bill”;


friends["bad"]=”Masha”;



var bestFriend:String= friends[“best”]




friends.best=”Alex”;



Another syntax:


var car:Object = {make:”Toyota”, model:”Camry”};


trace (car["make"], car.model);


// Output: Toyota Camry



Hoisting




n/a



Compiler moves all variable declarations to the top of the function, so you can use a variable name even before it’s been explicitly declared in the code.



Instantiation objects from classes



Customer cmr = new Customer();




Class cls = Class.forName(“Customer”);


Object myObj= cls.newInstance();



var cmr:Customer = new Customer();



var cls:Class = flash.util.getClassByName(“Customer”);

var myObj:Object = new cls();



Private classes



private class myClass{



There is no private classes in AS3.




Private constructors




Supported. Typical use: singleton classes.



Not available. Implementation of private constructors is postponed as they are not the part of the ECMAScript standard yet.


To create a Singleton, use public static getInstance(), which sets a private flag instanceExists after the first instantiation. Check this flag in the public constructor, and if instanceExists==true, throw an error.



Class and file names



A file can have multiple class declarations, but only one of them can be public, and the file must have the same name as this class.



A file can have multiple class declarations, but only one of them can be placed inside the package declaration, and the file must have the same name as this class.



What can be placed in a package



Classes and interfaces




Classes, interfaces, variables, functions, namespaces, and executable statements.



Dynamic classes (define an object that can be altered at runtime by adding or changing properties and methods).



n/a



dynamic class Person {



var name:String;


}


//Dynamically add a variable // and a function


var p:Person = new Person();


p.name=”Joe”;


p.age=25;


p.printMe = function () {


trace (p.name, p.age);


}



p.printMe(); // Joe 25



function closures



n/a. Closure is a proposed addition to Java 7.



myButton.addEventListener(“click”, myMethod);



A closure is an object that represents a snapshot of a function with its lexical context (variable’s values, objects in the scope). A function closure can be passed as an argument and executed without being a part of any object



Abstract classes



supported



n/a



Function overriding



supported



Supported. You must use the override qualifier




Function overloading



supported



Not supported.



Interfaces



class A implements B{


interfaces can contain method declarations and final variables.



class A implements B{


interfaces can contain only function declarations.



Exception handling




Keywords: try, catch, throw, finally, throws



Uncaught exceptions are propagated to the calling method.



Keywords: try, catch, throw, finally



A method does not have to declare exceptions.



Can throw not only Error objects, but also numbers:



throw 25.3;



Flash Player terminates the script in case of uncaught exception.




Regular expressions




Supported



Supported



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