Below is a short comparison table of major elements/concepts of these two languages for a quick reference.
You can read this table either left-to-right or right-to-left, depending on what’s your primary programming language is today.
This list is not complete, and your input is appreciated.
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Concept/Language Construct
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Java 5.0
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ActionScript 3.0
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Class library packaging
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.jar
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.swc
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Inheritance
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class Employee extends Person{…}
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class Employee extends Person{…}
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Variable declaration and initialization
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String firstName=”John”;
Date shipDate=new Date();
int i;
int a, b=10;
double salary;
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var firstName:String=”John”;
var shipDate:Date=new Date();
var i:int;
var a:int, b:int=10;
var salary:Number;
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Undeclared variables
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n/a
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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:*;
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Variable scopes
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block: declared within curly braces,
local: declared within a method or a block
member: declared on the class level
no global variables
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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.
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Strings
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Immutable, store sequences of two-byte Unicode characters
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Immutable, store sequences of two-byte Unicode characters
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Terminating statements with semicolons
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A must
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If you write one statement per line you can omit it.
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Strict equality operator
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n/a
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===
for strict non-equality use
!==
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Constant qualifier
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The keyword final
final int STATE=”NY”;
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The keyword const
const STATE:int =”NY”;
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Type checking
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Static (checked at compile time)
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Dynamic (checked at run-time) and static (it’s so called ‘strict mode’, which is default in Flex Builder)
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Type check operator
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instanceof
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is – checks data type, i.e. if (myVar is String){…}
The is operator is a replacement of older instanceof
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The as operator
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n/a
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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
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Primitives
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byte, int, long, float, double,short, boolean, char
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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);
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Complex types
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n/a
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Array, Date, Error, Function, RegExp, XML, and XMLList
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Array declaration and instantiation
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int quarterResults[];
quarterResults =
new int[4];
int quarterResults[]={25,33,56,84};
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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).
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The top class in the inheritance tree
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Object
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Object
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Casting syntax: cast the class Object to Person:
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Person p=(Person) myObject;
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var p:Person= Person(myObject);
or
var p:Person= myObject as Person;
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upcasting
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class Xyz extends Abc{}
Abc myObj = new Xyz();
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class Xyz extends Abc{}
var myObj:Abc=new Xyz();
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Un-typed variable
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n/a
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var myObject:*
var myObject:
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packages
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package com.xyz;
class myClass {…}
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package com.xyz{
class myClass{…}
}
ActionScript packages can include not only classes, but separate functions as well
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Class access levels
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public, private, protected
if none is specified, classes have package access level
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public, private, protected
if none is specified, classes have internal access level (similar to package access level in Java)
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Custom access levels: namespaces
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n/a
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Similar to XML namespaces.
namespace abc;
abc function myCalc(){}
or
abc::myCalc(){}
use namespace abc ;
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Console output
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System.out.println();
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// in debug mode only
trace();
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imports
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import com.abc.*;
import com.abc.MyClass;
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import com.abc.*;
import com.abc.MyClass;
packages must be imported even if the class names are fully qualified in the code.
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Unordered key-value pairs
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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
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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
|
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Hoisting
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n/a
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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.
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Instantiation objects from classes
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Customer cmr = new Customer();
Class cls = Class.forName(“Customer”);
Object myObj= cls.newInstance();
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var cmr:Customer = new Customer();
var cls:Class = flash.util.getClassByName(”Customer”);
var myObj:Object = new cls(); |
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Private classes
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private class myClass{…}
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There is no private classes in AS3.
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Private constructors
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Supported. Typical use: singleton classes.
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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.
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Class and file names
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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.
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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.
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What can be placed in a package
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Classes and interfaces
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Classes, interfaces, variables, functions, namespaces, and executable statements.
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Dynamic classes (define an object that can be altered at runtime by adding or changing properties and methods).
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n/a
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dynamic class Person {
var name:String;
}
//Dynamically add a variable // and a function
Person p= new Person();
p.name=”Joe”;
p.age=25;
p.printMe = function () {
trace (p.name, p.age);
}
p.printMe(); // Joe 25
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function closures
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n/a. Closure is a proposed addition to Java 7.
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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
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Abstract classes
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supported
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n/a
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Function overriding
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supported
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Supported. You must use the override qualifier
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Function overloading
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supported
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Not supported.
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Interfaces
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class A implements B{…}
interfaces can contain method declarations and final variables.
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class A implements B{…}
interfaces can contain only function declarations.
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Exception handling
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Keywords: try, catch, throw, finally, throws
Uncaught exceptions are propagated to the calling method.
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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.
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Regular expressions
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Supported
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Supported
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Thanks,
Yakov Fain
19 Comments
Thanks!
Yakov
That’s one of the great missing in as for me…
b) specifying the exclusive data type it must store
http://www.dannypatterson.com/Resources/Blog/EntryDetail.cfm?id=98
trace(”i=”+i);
}
trace (”i====”+i);
This was an extra line (copy/paste error) in the AS3 column. Fixed
abc::myCalc(){}
For example:
case “ALPHA”:
trace(”alpha”);break;
trace(”beta”);break;
public class Test {
public static void main(String args[]) {
CASES selector = CASES.ALPHA;
switch ( selector ) {
case ALPHA: System.out.println(”alpha”); break;
case BETA: System.out.println(”beta”); break;
}
}
}