\/\/hello.groovy
\n<\/FONT><\/SPAN>println “hello, world”
<\/FONT><\/SPAN>
\nfor<\/FONT><\/SPAN> (arg in this<\/FONT><\/SPAN>.args ) {
\n println “Argument:”<\/FONT><\/SPAN> + arg;
\n}
\n\/\/ <\/FONT>this<\/FONT><\/SPAN> is a comment
\n<\/FONT><\/SPAN>\/* a block comment, commenting out an alternative to above:
\nthis<\/FONT><\/SPAN>.args.each{ arg -> println “hello, ${arg}”<\/FONT><\/SPAN>}
\n*\/
<\/PRE><\/DIV><\/DIV>
\nTo run it from command line<\/P>
\n
\ngroovy hello.groovy MyName yourName HisName<\/PRE><\/DIV><\/DIV><\/DIV>
\n
\n<\/A>Overview<\/H2>
\nGroovy 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.<\/P>
\n
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…<\/P>
\n
\ndef list = [1, 2, ‘hello’, new<\/FONT><\/SPAN> java.util.Date()]
\nassert<\/FONT><\/SPAN> list.size() == 4
\nassert<\/FONT><\/SPAN> list.get(2) == ‘hello’
\nassert<\/FONT><\/SPAN> list[2] == ‘hello’
<\/PRE><\/DIV><\/DIV>
\nNotice that everything is an object (or that auto-boxing takes place when working with numbers). To create maps…<\/P>
\n
\ndef map = [‘name’:’James’, ‘location’:’London’]
\nassert<\/FONT><\/SPAN> map.size() == 2
\nassert<\/FONT><\/SPAN> map.get(‘name’) == ‘James’
\nassert<\/FONT><\/SPAN> map[‘name’] == ‘James’
<\/PRE><\/DIV><\/DIV>
\nIterating over collections is easy…
<\/P>
\n
\ndef list = [1, 2, 3]
\nfor<\/FONT><\/SPAN> (i in list) { println i }
<\/PRE><\/DIV><\/DIV>
\nOnce you have some collections you can then use some of the new collection helper methods or try working with closures…<\/P><\/DIV>
\n
\n<\/A>Working with closures<\/H2>
\nClosures 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…<\/P>
\n
\ndef closure = { param -> println(“hello ${param}”<\/FONT><\/SPAN>) }
\nclosure.call(“world!”<\/FONT><\/SPAN>)
<\/p>\nclosure = { greeting, name -> println(greeting + name) }
\nclosure.call(“hello “<\/FONT><\/SPAN>, “world!”<\/FONT><\/SPAN>)
<\/PRE><\/DIV><\/DIV>
\nIf no parameter(s) is(are) specified before -> symbol then a default named parameter, called ‘it’ can be used. e.g.
<\/P>
\n
\ndef closure = { println “hello “<\/FONT><\/SPAN> + it }
\nclosure.call(“world!”<\/FONT><\/SPAN>)
<\/PRE><\/DIV><\/DIV>
\nUsing closures allows us to process collections (arrays, maps, strings, files, SQL connections and so forth) in a clean way. e.g
<\/P>
\n
\n[1, 2, 3].each ({ item -> print “${item}-“<\/FONT><\/SPAN> })
\n[“k1”<\/FONT><\/SPAN>:“v1”<\/FONT><\/SPAN>, “k2”<\/FONT><\/SPAN>:“v2”<\/FONT><\/SPAN>].each {key, value -> println key + “=”<\/FONT><\/SPAN> + value}<\/PRE><\/DIV><\/DIV>
\nNote:<\/B> 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:<\/P>
\n
\ndef fun(int<\/FONT><\/SPAN> i, Closure c) {
\n c.call(i)
\n}
<\/p>\n\/\/ put Closure out of ()
\n<\/FONT><\/SPAN>[1, 2, 3].each() { item -> print “${item}-“<\/FONT><\/SPAN> } \/\/ 1-2-3-
\n<\/FONT><\/SPAN>fun(123) { i -> println i } \/\/ 123
<\/FONT><\/SPAN>
\n\/\/ omit ()<\/FONT><\/SPAN><\/PRE><\/DIV><\/DIV><\/FONT><\/SPAN>
\n
<\/FONT><\/SPAN>[1, 2, 3].each ({ item -> print “${item}-“<\/FONT><\/SPAN> }) \/\/ 1-2-3-<\/FONT><\/SPAN><\/DIV>
\n
<\/FONT><\/SPAN>
\/\/ omit enclosing ()
<\/FONT><\/SPAN>[1, 2, 3].each { item -> print “${item}-“<\/FONT><\/SPAN> } \/\/ 1-2-3-
<\/FONT><\/SPAN>
\/\/ normal
<\/FONT><\/SPAN>[1, 2, 3].each(({ item -> print “${item}-“<\/FONT><\/SPAN> })) \/\/ 1-2-3-
<\/FONT><\/SPAN>
\/\/ using the fun function to <\/FONT>do<\/FONT><\/SPAN> the same thing
<\/FONT><\/SPAN>[1,2,3].each {fun(it,{item -> print “${item}-“<\/FONT><\/SPAN>})} \/\/ 1-2-3-
<\/FONT><\/SPAN>
def closure = { i -> println i}
\/\/[1, 2, 3].each() closure \/\/ error. closure has been previously defined<\/FONT><\/SPAN><\/DIV>
\nHere are a number of helper methods available on collections & strings…<\/P>
\n
\n<\/A>each<\/H3>
\niterate via a closure<\/P>
\n
\n[1, 2, 3].each { item -> print “${item}-“<\/FONT><\/SPAN> }<\/PRE><\/DIV><\/DIV><\/DIV>
\n
\n<\/A>collect<\/H3>
\ncollect the return value of calling a closure on each item in a collection<\/P>
\n
\ndef value = [1, 2, 3].collect { it * 2 }
\nassert<\/FONT><\/SPAN> value == [2, 4, 6]<\/PRE><\/DIV><\/DIV><\/DIV>
\n
\n<\/A>find<\/H3>
\nfinds first item matching closure predicate<\/P>
\n
\ndef value = [1, 2, 3].find { it > 1 }
\nassert<\/FONT><\/SPAN> value == 2<\/PRE><\/DIV><\/DIV><\/DIV>
\n
\n<\/A>findAll<\/H3>
\nfinds all items matching closure predicate<\/P>
\n
\ndef value = [1, 2, 3].findAll { it > 1 }
\nassert<\/FONT><\/SPAN> value == [2, 3]<\/PRE><\/DIV><\/DIV><\/DIV>
\n
\n<\/A>inject<\/H3>
\nallows 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<\/P>
\n
\ndef value = [1, 2, 3].inject(‘counting: ‘) { str, item -> str + item }
\nassert<\/FONT><\/SPAN> value == “counting: 123”<\/FONT><\/SPAN><\/p>\nvalue = [1, 2, 3].inject(0) { count, item -> count + item }
\nassert<\/FONT><\/SPAN> value == 6<\/PRE><\/DIV><\/DIV>
\nIn addition there’s 2 new methods for doing boolean logic on some collection…<\/P><\/DIV>
\n
\n<\/A>every<\/H3>
\nreturns true if all items match the closure predicate<\/P>
\n
\ndef value = [1, 2, 3].every { it < 5 }
\nassert<\/FONT><\/SPAN> value<\/p>\nvalue = [1, 2, 3].every { item -> item < 3 }
\nassert<\/FONT><\/SPAN> ! value<\/PRE><\/DIV><\/DIV><\/DIV>
\n
\n<\/A>any<\/H3>
\nreturns true if any item match the closure predicate<\/P>
\n
\ndef value = [1, 2, 3].any { it > 2 }
\nassert<\/FONT><\/SPAN> value<\/p>\nvalue = [1, 2, 3].any { item -> item > 3 }
\nassert<\/FONT><\/SPAN> value == false<\/FONT><\/SPAN><\/PRE><\/DIV><\/DIV>
\nOther helper methods include:<\/P><\/DIV>
\n
\n<\/A>max \/ min<\/H3>
\nreturns the max\/min values of the collection – for Comparable objects<\/P>
\n
\nvalue = [9, 4, 2, 10, 5].max()
\nassert<\/FONT><\/SPAN> value == 10
\nvalue = [9, 4, 2, 10, 5].min()
\nassert<\/FONT><\/SPAN> value == 2
\nvalue = [‘x’, ‘y’, ‘a’, ‘z’].min()
\nassert<\/FONT><\/SPAN> value == ‘a’
<\/PRE><\/DIV><\/DIV><\/DIV>
\n
\n<\/A>join<\/H3>
\nconcatenates the values of the collection together with a string value<\/P>
\n
\ndef value = [1, 2, 3].join(‘-‘)
\nassert<\/FONT><\/SPAN> value == ‘1-2-3’<\/PRE><\/DIV><\/DIV><\/DIV><\/DIV><\/DIV><\/p>\n","protected":false},"excerpt":{"rendered":"Your First Groovy \/\/hello.groovy println “hello, world” for (arg in this.args ) { println “Argument:” + arg; } \/\/ this is a comment \/* a block comment, commenting out an alternative to above: this.args.each{ arg -> println “hello, ${arg}”} *\/ To run it from command line groovy hello.groovy MyName yourName HisName Overview Groovy classes compile … Continue reading Your First Groovy<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[120],"class_list":["post-464","post","type-post","status-publish","format-standard","hentry","category-linux","tag-groovy"],"_links":{"self":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts\/464","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=464"}],"version-history":[{"count":1,"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts\/464\/revisions"}],"predecessor-version":[{"id":906,"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts\/464\/revisions\/906"}],"wp:attachment":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=464"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=464"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=464"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}