Java5和ActionScript3的語法比較

原帖在 Comparing the syntax of Java 5 and ActionScript 3

下表列出了兩種語言的主要元素、概念的比較，以供參考。你可以從左向右或從右向左進行閱讀。該列表並不完善，可在評論中添加。

Concept/Language Construct	Java 5.0	ActionScript 3.0
類庫打包	.jar	.swc
繼承 Inheritance	class Employee extends Person{…}	class Employee extends Person{…}
變量的聲明與初始化 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;
未聲明變量 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.即任意類型。 A default value: undefined var myVar:*;
變量作用域 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.
字符串 Strings	Immutable, store sequences of two-byte Unicode characters	Immutable, store sequences of two-byte Unicode characters
語句結束符（;）	必須 A must	可省略 If you write one statement per line you can omit it.
嚴格相等運算符     Strict equality operator	n/a	=== for strict non-equality use !==
常數 Constant qualifier	The keyword final   final int STATE=”NY”;	The keyword const   const STATE:int =”NY”;
類型檢查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)
類型檢查運算符Type check operator	instanceof	is – checks data type, i.e. if (myVar is String){…} The is operator is a replacement of older instanceof
as運算符 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
基本數據類型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);
複雜數據類型Complex types	n/a	Array, Date, Error, Function, RegExp, XML, and XMLList
數組聲明與初始化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]; 關聯數組AS3 also has associative arrays that uses named elements instead of numeric indexes (similar to Hashtable).
根類 The top class in the inheritance tree	Object	Object
類型轉換 Casting syntax: cast the class Object to Person:	Person p=(Person) myObject;	var p:Person= Person(myObject); or var p:Person= myObject as Person;
類型向上轉換upcasting	class Xyz extends Abc{} Abc myObj = new Xyz();	class Xyz extends Abc{} var myObj:Abc=new Xyz();
無類型變量Un-typed variable	n/a	var myObject:* var myObject:
包packages	package com.xyz; class myClass {…}	package com.xyz{ class myClass{…} } ActionScript packages can include not only classes, but separate functions as well
類訪問層次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)
命名空間Custom access levels: namespaces	n/a	Similar to XML namespaces. namespace abc; abc function myCalc(){} or abc::myCalc(){} use namespace abc ;
控制檯輸出Console output	System.out.println();	// in debug mode only trace();
imports導入	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.
無序鍵值對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關聯數組   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.
對象實例化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();
私有類Private classes	private class myClass{…}	There is no private classes in AS3.
私有構造函數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.
類和文件名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.
包What can be placed in a package	Classes and interfaces	Classes, interfaces, variables, functions, namespaces, and executable statements.
動態類 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
函數閉包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
抽象類Abstract classes	supported	n/a
函數覆蓋Function overriding	supported	Supported. You must use the override qualifier
函數重載Function overloading	supported	Not supported.
接口Interfaces	class A implements B{…} interfaces can contain method declarations and final variables.	class A implements B{…} interfaces can contain only function declarations.
異常處理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.
正則表達式Regular expressions	Supported	Supported