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= Iterator Pattern


The http://en.wikipedia.org/wiki/Iterator_pattern[Iterator Pattern] allows sequential access to the elements of an aggregate object without exposing its underlying representation.

Groovy has the iterator pattern built right in to many of its closure operators, e.g. `each` and `eachWithIndex` as well as the `for .. in` loop.

For example:

[source,groovy]
----
include::{projectdir}/src/spec/test/DesignPatternsTest.groovy[tags=iterator_example,indent=0]
----

Results in the output:

----
1
2
3
4
May=31
Mar=31
Apr=30
java.awt.Color[r=0,g=0,b=0]
java.awt.Color[r=255,g=255,b=255]
----

Another example:

[source,groovy]
----
include::{projectdir}/src/spec/test/DesignPatternsTest.groovy[tags=iterator_example2,indent=0]
----

Results in:

----
Position 0 contains 'java.awt.Color[r=0,g=0,b=0]'
Position 1 contains 'java.awt.Color[r=255,g=255,b=255]'
----

The iterator pattern is also built in to other special operators such as the `eachByte`, `eachFile`, `eachDir`, `eachLine`, `eachObject`, `eachMatch` operators for working with streams, URLs, files, directories and regular expressions matches.