Iterators

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Iterators

• Dan Fleck

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Iterators

• Iterator
• Object that can access a collection of objects
  one object at a time
• Traverses the collection of objects
• JCF defines generic interface java.util.Iterator
• And a subinterface ListIterator

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Iterator Example

• ArrayList aList new ArrayList()
• populateListWithStrings(aList)
• Iterator itr aList.iterator()
• while (itr.hasNext())
• String nextStr (String)itr.next()
• System.out.printf(List item is s, nextStr)

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Iterator Example with Generics

• ArrayListltStringgt aList new ArrayListltStringgt()
  
• populateListWithStrings(aList)
• IteratorltStringgt itr aList.iterator()
• while (itr.hasNext())
• String nextStr itr.next()
• System.out.printf(List item is s, nextStr)

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Iterator methods

• See Javadoc for Iterator
• Do all Iterators implement the remove operation?
  What happens if they dont?
• What is another way to iterate through a
  Collection (ArrayList, Vector, Set, HashSet,
  LinkedList, etc)?

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ListIterator

• Extends iterator to allow
• reverse iteration of a List
• hasPrevious(), previous methods
• Has an add() method
• Has a set() method to replace elements
• Lets you get the index of the element
• Int nextIndex(), int previousIndex()