Data commit

Task/Queue-Usage/Groovy/queue-usage-1.groovy

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+def q = new LinkedList()

Task/Queue-Usage/Groovy/queue-usage-2.groovy

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+assert q.empty
+println q
+// "push" adds to end of "queue" list
+q.push('Stuart')
+println q
+assert !q.empty
+// "add" adds to end of "queue" list
+q.add('Pete')
+println q
+assert !q.empty
+// left shift operator ("<<") adds to end of "queue" list
+q << 'John'
+println q
+assert !q.empty
+// add assignment ("+=") adds the list elements
+// to the end of the "queue" list in list order
+q += ['Paul', 'George']
+println q
+assert !q.empty
+// "poll" removes and returns the first element in the
+// "queue" list ("pop" exists for Groovy lists, but it
+// removes and returns the LAST element for "Stack"
+// semantics). "poll" only exists in objects that
+// implement java.util.Queue, like java.util.LinkedList
+assert q.poll() == 'Stuart'
+println q
+assert !q.empty
+assert q.poll() == 'Pete'
+println q
+assert !q.empty
+q << 'Ringo'
+println q
+assert !q.empty
+assert q.poll() == 'John'
+println q
+assert !q.empty
+assert q.poll() == 'Paul'
+println q
+assert !q.empty
+assert q.poll() == 'George'
+println q
+assert !q.empty
+assert q.poll() == 'Ringo'
+println q
+assert q.empty
+assert q.poll() == null