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<p>Groovy has native language support for collections, lists, maps and arrays.</p><h2>Lists</h2><p>You can create lists as follows. Notice that [] is the empty list expression.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def list = [5, 6, 7, 8]
assert list.get(2) == 7
assert list[2] == 7
assert list instanceof java.util.List

def emptyList = []
assert emptyList.size() == 0
emptyList.add(5)
assert emptyList.size() == 1
</pre></td></tr></table><p>Each list expression creates an implementation of <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/util/List.html">java.util.List</a>.</p><p>See <a href="http://groovy.codehaus.org/JN1015-Collections">Lists and Sets</a> for more information on using Lists.</p><h2>Ranges</h2><p>Ranges allow you to create a list of sequential values. These can be used as Lists since <a href="http://groovy.codehaus.org/apidocs/groovy/lang/Range.html">Range</a> extends <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/util/List.html">java.util.List</a>.<br /> Ranges defined with the <em>..</em> notation are inclusive (that is the list contains the from and to value).<br /> Ranges defined with the <em>..&lt;</em> notation are half-open, they include the first value but not the last value.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>// an inclusive range
def range = 5..8
assert range.size() == 4
assert range.get(2) == 7
assert range[2] == 7
assert range instanceof java.util.List
assert range.contains(5)
assert range.contains(8)

// lets use a half-open range
range = 5..&lt;8
assert range.size() == 3
assert range.get(2) == 7
assert range[2] == 7
assert range instanceof java.util.List
assert range.contains(5)
assert ! range.contains(8)

//get the end points of the range without using indexes
def range = 1..10
assert range.from == 1
assert range.to == 10
</pre></td></tr></table><p>Note that ranges are implemented efficiently, creating a lightweight Java object containing a from and to value.</p><p>Ranges can be used for any Java object which implements <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Comparable.html">java.lang.Comparable</a> for comparison and also have methods next() and previous() to return the next / previous item in the range.<br /> e.g. you can use Strings in a range</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>// an inclusive range
def range = 'a'..'d'
assert range.size() == 4
assert range.get(2) == 'c'
assert range[2] == 'c'
assert range instanceof java.util.List
assert range.contains('a')
assert range.contains('d')
assert ! range.contains('e')
</pre></td></tr></table><p>Ranges can be used to iterate using the for statement.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>for (i in 1..10) {
  println "Hello ${i}"
}
</pre></td></tr></table><p>but alternatively you can achieve the same effect, by iterating a range with <em>each</em> method:</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>(1..10).each { i ->
  println "Hello ${i}"
}
</pre></td></tr></table><p>Ranges can be also used in the <code>switch</code> statements:</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>switch (years) {
   case 1..10: interestRate = 0.076; break;
  case 11..25: interestRate = 0.052; break;
      default: interestRate = 0.037;
}
</pre></td></tr></table><h2>Maps <img class="editor-inline-macro" src="/plugins/servlet/confluence/placeholder/macro?definition=e2FuY2hvcjptYXBzfQ&amp;locale=en_GB&amp;version=2" data-macro-name="anchor" data-macro-default-parameter="maps"></h2><p>Maps can be created using the following syntax. Notice that [:] is the empty map expression.</p><p>Map keys are strings by default: [a:1] is equivalent to [&quot;a&quot;:1]. But if you really want a variable to become the key, you have to wrap it between parentheses: [(a):1].</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def map = [name:"Gromit", likes:"cheese", id:1234]
assert map.get("name") == "Gromit"
assert map.get("id") == 1234
assert map["name"] == "Gromit"
assert map['id'] == 1234
assert map instanceof java.util.Map

def emptyMap = [:]
assert emptyMap.size() == 0
emptyMap.put("foo", 5)
assert emptyMap.size() == 1
assert emptyMap.get("foo") == 5
</pre></td></tr></table><p>Maps also act like beans so you can use the property notation to get/set items inside the Map provided that the keys are Strings which are valid Groovy identifiers.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def map = [name:"Gromit", likes:"cheese", id:1234]
assert map.name == "Gromit"
assert map.id == 1234

def emptyMap = [:]
assert emptyMap.size() == 0
emptyMap.foo = 5
assert emptyMap.size() == 1
assert emptyMap.foo == 5
</pre></td></tr></table><p>Note: by design map.foo will always look for the key foo in map. This means foo.class will return null on an empty map and not result in calling the method getClass()</p><p>See <a href="http://groovy.codehaus.org/JN1035-Maps">Maps</a> for more information on using maps.</p><h2>Getting efficient with the star-dot '*.' operator</h2><p>You can perform operations on all the members of a collection using the '*.' operator, e.g.:</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>assert [1, 3, 5] == ['a', 'few', 'words']*.size()
</pre></td></tr></table><h2>Enhanced Collection Methods</h2><p>In addition to providing the literal syntax for collections, Groovy adds some additional methods to make working with collections more convenient. As an example, you can find big words from a list as follows:</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def words = ['ant', 'buffalo', 'cat', 'dinosaur']
assert words.findAll{ w -> w.size() > 4 } == ['buffalo', 'dinosaur']
</pre></td></tr></table><p>Or you can find the first letters of some words as follows:</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def words = ['ant', 'buffalo', 'cat', 'dinosaur']
assert words.collect{ it[0] } == ['a', 'b', 'c', 'd']
</pre></td></tr></table><p>In addition to findAll and collect shown above, you have methods like findIndexOf, grep, any, every, min, max, flatten, intersect, disjoint, sort, join and others. Simply look up the <a href="http://groovy.codehaus.org/groovy-jdk/">GDK doco</a> for more details. You might want to look up the added methods for Collection, List and Object to start with.</p><p>Some more details about these methods can also be found in the Quick Start Guide under <a class="confluence-link" href="/display/GROOVY/JN1015-Collections" data-linked-resource-id="75027" data-linked-resource-type="page" data-linked-resource-default-alias="JN1015-Collections" data-base-url="http://docs.codehaus.org">JN1015-Collections</a>.</p><h2>Slicing with the subscript operator</h2><p>You can index into Strings, Lists, arrays, Maps, regexs and such like using the subscript expression.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def text = "nice cheese gromit!"
def x = text[2]

assert x == "c"
assert x.class == String

def sub = text[5..10]
assert sub == 'cheese'

def map = [name:"Gromit", likes:"cheese", id:1234]

assert map["name"] == "Gromit"
assert map.name == "Gromit"

def list = [10, 11, 12]
def answer = list[2]
assert answer == 12
</pre></td></tr></table><p>Notice that you can use ranges to extract part of a List/array/String/regex. This is often referred to as <em>slicing</em> in scripting languages like Python. You can also use a list of indexes too.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def list = 100..200
def sub = list[1, 3, 20..25, 33]
assert sub == [101, 103, 120, 121, 122, 123, 124, 125, 133]
</pre></td></tr></table><p>You can update items using the subscript operator too</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def list = ["a", "b", "c"]
list[2] = "d"
list[0] = list[1]
list[3] = 5
assert list == ["b", "b", "d", 5]
</pre></td></tr></table><p>You can use negative indices to count from the end of the List, array, String etc.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def text = "nice cheese gromit!"
def x = text[-1]
assert x == "!"

def name = text[-7..-2]
assert name == "gromit"
</pre></td></tr></table><p>Also if you use a backwards range (the starting index is greater than the end index) then the answer is reversed.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def text = "nice cheese gromit!"
def name = text[3..1]
assert name == "eci"
</pre></td></tr></table><h2>Dynamic objects (Expandos)</h2><p>The Expando is not a collection in the strictest sense, but in some ways it is similar to a Map, or objects in JavaScript that do not have to have their properties defined in advance. It allows you to create dynamic objects by making use of Groovy's <a class="confluence-link" href="/display/GROOVY/Closures+-+Informal+Guide" data-linked-resource-id="2729" data-linked-resource-type="page" data-linked-resource-default-alias="Closures - Informal Guide" data-base-url="http://docs.codehaus.org">closure mechanisms</a>. An <a href="http://groovy.codehaus.org/gapi/groovy/util/Expando.html">Expando</a> is different from a map in that you can provide synthetic methods that you can call on the object.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>def player = new Expando()
player.name = "Dierk"
player.greeting = { "Hello, my name is $name" }

println player.greeting()
player.name = "Jochen"
println player.greeting()
</pre></td></tr></table><p>The player.greeting assignment passes in a <a class="confluence-link" href="/display/GROOVY/Closures+-+Informal+Guide" data-linked-resource-id="2729" data-linked-resource-type="page" data-linked-resource-default-alias="Closures - Informal Guide" data-base-url="http://docs.codehaus.org">closure</a> to execute when greeting() is called on the <a href="http://groovy.codehaus.org/gapi/groovy/util/Expando.html">Expando</a>. Notice that the closure has access to the properties assigned to the <a href="http://groovy.codehaus.org/gapi/groovy/util/Expando.html">Expando</a>, even though these values may change over time, using Groovy's <a class="confluence-link" href="/display/GROOVY/Strings+and+GString" data-linked-resource-id="2771" data-linked-resource-type="page" data-linked-resource-default-alias="Strings and GString" data-base-url="http://docs.codehaus.org">GString</a> &quot;$variableOrProperty&quot; notation.</p>