Java, Groovy & Scala: side to side 2

最新推荐文章于 2025-06-09 11:36:18 发布

最新推荐文章于 2025-06-09 11:36:18 发布 · 130 阅读

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Java, Groovy & Scala: side to side 2

Posted By: Andres Almiray on Thu. Jun. 12, 2008

Second part of the series, (first part here). Thanks a lot to Daniel Spiewak who took the time to expand the topics presented about Scala. Without further ado...

Feature	Java	Groovy	Scala
Instance Fields	[access_modifier] Type name where access_modifier is any of public protected private empty - means package protected [default access]	[access_modifier] Type name where access_modifier is any of public [default access] protected private If no access modifier is provided then the field would be promoted to a property. Properties have their get/set methods auto generated in bytecode which means that the following Groovy class class Person { String name } Is equivalent to the following Java class public class Person { private String name; public void setName( String name ) { this .name = name; } public String getName() { return name; } }	[access_modifier] [definition] name: Type where access_modifier is any of empty - [default access] protected private where definition is any of var - mutable val - immutable (think final in Java) private works as in Java protected baffles me, as a subclass can't access its parent's protected fields (perhaps I missed something here), same thing with empty access modifier (strong encapsulation?)
Class Fields (static)	[access_modifier] static Type name where access_modifier is any of public protected private empty - means package protected [default access]	[access_modifier] static Type name where access_modifier is any of public protected private	No static modifier (?) but object can be used object Foo { val aConstant = "Foo" private var seed = 42 def foo() = { seed += 1; seed - 1 } } object Bar { import Foo._ def main(args: Array[String]) { var bar = foo() println( aConstant ) // Foo println( bar ) // 42 println( foo() ) // 43 } }
Global Variables	Not supported. Every field/constant must belong to a class	Supported only in scripts, otherwise follows Java rules	Not supported. Every field/constant must belong to a class
Method definition	class Person { [access_modifier] Type name() { // statements } } where access_modifier is any of public protected private empty - means package protected [default access]	class Person { [access_modifier] Type name() { // statements } } where access_modifier is any of public protected private empty - same as public [default access]	class Person { [access_modifier] def name() [:Type] = { // statements } } where access_modifier is any of protected private empty - public? [default access] The type of the method may be optional No-arg methods can be written and called without parens class Person { def name = { "Scala" } } ... // this is a method call new Person().name
Static Method Definition	class Person { [access_modifier] static Type name() { // statements } } where access_modifier is any of public protected private empty - same as public [default access]	class Person { [access_modifier] static Type name() { // statements } } where access_modifier is any of public protected private empty - same as public [default access]	Follows the rules of Class Fields and Method Definition
Returning from a method	return expression; return ;	Same as Java. But can leave the return statement - in that case the last expression evaluated is returned.	Same as Java. But can leave the return statement - in that case the last expression evaluated is returned.
Null	null	null - Guillaume Laforge notes that "Null Object Pattern" is supported in Groovy. See also: NullObject. So, you can call null.toString() for example.	null Which is actually of type Null , the only one of its kind. Can't call methods on it.
Arrays	int [] a = new int[10]; a[0] = 3;	int [] a = new int[10] a[0] = 3	var a:Array[Int] = new Array(10) a(0) = 3 also var a = new Array[Int](10) a(0) = 3
Array Literals	int[] a = {0,1,2}; a[0] = 3;	int [] a = [0,1,2] a[0] = 3	val nums = Array(0,1,2)
Lists	Supported by the Collections framefork (JSL), not really part of the language	List list = [0,1,2] list[0] = 'Foo' list[10] = 11 Lists can be heterogeneous Lists grow as needed	val nums = List(1,2,3,4) Lists are immutable, values can't be reassigned List are homogeneous
Hash Literals	Not supported. (See java.util.Map)	def hash = [key:'value', 'id': 1] hash.key = 'value2' // bean like access hash[key] = 'value3' // hash like access	val nums = Map("one" -> 1, "two" -> 2, "three" -> 3) nums("one") // 1 nums("two") // 2 Daniel explains: Scala does have a syntax for map literals (sort of), but it's not really built into the language. It's actually an implicit conversion on Any (common superclass of all objects incl. primitives) and a symbolic method.