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Your First Groovy

To run it from command line

Overview

Groovy classes compile down to Java bytecode and so there's a 1-1 mapping between a Groovy class and a Java class.
Indeed each Groovy class can be used inside normal Java code - since it is a Java class too.

Probably the easiest way to get groovy is to try working with collections. In Groovy List (java.util.List) and Map (java.util.Map) are both first class objects in the syntax. So to create a List of objects you can do the following...

Notice that everything is an object (or that auto-boxing takes place when working with numbers). To create maps...

Iterating over collections is easy...

Once you have some collections you can then use some of the new collection helper methods or try working with closures...

Working with closures

Closures are similar to Java's inner classes, except they are a single method which is invokable, with arbitrary parameters. A closure can have as many parameters as you wish...

If no parameter(s) is(are) specified before -> symbol then a default named parameter, called 'it' can be used. e.g.

Using closures allows us to process collections (arrays, maps, strings, files, SQL connections and so forth) in a clean way. e.g

Note: If a given closure is the last parameter of a method, its definition can reside outside of the parentheses. Thus the following code is valid:

Here are a number of helper methods available on collections & strings...

each

iterate via a closure

collect

collect the return value of calling a closure on each item in a collection

find

finds first item matching closure predicate

findAll

finds all items matching closure predicate

Error rendering macro 'code': Invalid value specified for parameter 'lang'
def value = [1, 2, 3].findAll { it > 1 }
assert value == [2, 3]

inject

allows you to pass a value into the first iteration and then pass the result of that iteration into the next iteration and so on. This is ideal for counting and other forms of processing

In addition there's 2 new methods for doing boolean logic on some collection...

every

returns true if all items match the closure predicate

any

returns true if any item match the closure predicate

Other helper methods include:

max / min

returns the max/min values of the collection - for Comparable objects

join

concatenates the values of the collection together with a string value

Also the 'yield' style of creating iterators, available in Python and Ruby via the yield statement, is available. The only difference is rather than using a yield statement, we're just using closures.

outputs
A-B-C-

The use of Closure in the method prototype is optional. If we have syntax sugar for invoking closures as if they are method calls, then the generator method could look even more like the python/ruby equivalent. Especially if parentheses are optional...

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