Java, Groovy & Scala: side to side 1
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Java, Groovy & Scala: side to side 1
Posted By: Andres Almiray on Wed. Jun. 11, 2008
This is the first part of the series. I shamelessly borrowed Sundar's layout and categorization. These are the language versions I'm testing the code with in case anyone is interested
· Java - Java5 (jdk1.6.0_06/jre1.6.0._10)
· Groovy - 1.6-beta-2-SNAPSHOT
· Scala - 2.7.1.final
Disclaimer: I know Groovy better than I know Scala, if someone spots a mistake please let me know
Feature
Java
Groovy
Scala
Type System
Static with few dynamic checks inserted as needed.
Dynamic, optional static types.
Static, with type inference.
Comments
/* * multiline comment */ /** * javadoc comment */ // single line comment
/* * multiline comment */ /** * groovydoc comment */ // single line comment
/* * multiline comment */ /** * scaladoc comment */ // single line comment
End of statement
;
a new line will do most in most cases. Use ; when ambiguous
a new line will do most in most cases. Use ; when ambiguous
Control Statements - if
if (condition) { // statements } if (condition) { // statements } else if (condition) { // statements } else { // statements }
if (condition) { // statements } if (condition) { // statements } else if (condition) { // statements } else { // statements }
if (condition) { // statements } if (condition) { // statements } else if (condition) { // statements } else { // statements }
Control Statements - ternary operator
(condition) ? true_statement : false_statement
(condition) ? true_statement : false_statement Elvis operator, a refinement over the ternary operator. If the condition expression is true then said condition expression will be the true_statement condition ?: false_statement
if (condition) true_statement else false_statement
Control Statements - while
while (condition) { // statements } do { // statements } while (condition);
while (condition) { // statements }
while (condition) { // statements } do { // statements } while (condition)
Control Statements - for
for (init; condition; increment ) { // statements } for (Type t: iterable ) { // statements }
for (init; condition; increment ) { // statements } for (Type t: iterable ) { // statements } for ( variable in iterable ) { // statements } Every single object in Groovy is iterable, default impl returns the object itself
for ( t <- list-value ) { // statements } list-value may also be an Array for ( s ) yield statement s may be one of
- generator: val x <- e e is a list-value expression, binding x to successive values in the list
- definition: val x = e introduces x as a name for the value of e in the rest of the comprehension
- filter: a Boolean expression, omits all bindings (values?) for which the expression is false
@Tony Morris has more info at http://blog.tmorris.net/type-safe-scala-sequence-comprehensions
Control Statements - switch
switch (target) { case constant_expr: // statements [break] ... default: // statements }
switch (target) { case constant_expr: // statements [break] ... default: // statements } * target may be any object * case statements may use same expressions as in Java plus Strings, Matchers, regular expression, closures, ranges, any object that supports isCase()
Not supported Scala has a similar feature as Groovy's any object as case (case classes and matchers, they deserve a more detailed explanation)
Control Statements - conditions
conditions must be evaluated in a boolean context
conditions may be evaluated in many contexts, this is known as the Groovy Truth, some rules follow (this is not a complete set, please refer to Groovy in Action or Groovy's site) evaluates to false
- false
- null references
- empty Map
- empty List
- Matcher with no matches
conditions must be evaluated in a Boolean context
String Literals
"Hello Java"
"Hello Groovy" // double quote 'Hello Groovy' // single quoute """Hello Groovy""" // multiline // variable interpolation name = "Groovy" "Hello ${name}" // evals to Hello Groovy
"Hello Scala" """Hello Scala""" // multiline @Daniel mentions Scala supports triple-quote too
Class declaration
class HelloWorld { // fields // methods }
class HelloWorld { // fields // methods }
class HelloWorld { // fields // methods } // defines a singleton object object HelloWorld { // fields // methods }
原文链接http://groovygrails.com/gg/blog/view/123147;jsessionid=11297C7AB6F87D53BBBC1CEFBCA6B0AB.vhost01
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