Comparing the syntax of Java 5 and ActionScript 3

转自：http://flexblog.faratasystems.com/?p=115

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.

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 Person p= 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

Thanks,

Yakov Fain

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19 Comments

－－－－－－－－－－－－－－－－－－

呵呵，似乎是java/delphi的混血哦！！！:)