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 }