Linked Lists

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Chapter 7
Linked Lists
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myLinked.head
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myLinked.head
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myLinked.head
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newEntry
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newEntry
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An iterator is an object that enables a user to
loop through a collection without accessing the
collections fields.
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head
element next
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head
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To print myList in reverse order itr
myList.listIterator (myList.size( )) while
(itr.hasPrevious( )) System.out.println
(itr.previous( ))
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Another ListIterator method / Inserts an
element into the LinkedList in front of the
element that would be returned by next() and
in back of the element that would be returned by
previous(). / public void add (E
element)
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LinkedListltDoublegtmyList new LinkedListltDoublegt(
) myList.add (0.0) myList.add
(1.0) ListIteratorltDoublegt itr
myList.listIterator() itr.next() itr.add (0.8)
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The LinkedList would now have 0.0, 0.8, 1.0
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Another ListIterator method / Removes the
last returned element. / public void
remove()
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Users guide for choosing ArrayList or
LinkedList If the application entails a lot of
accessing and/or modifying elements at widely
varying indexes, an ArrayList will be much
faster than a LinkedList. If a large part of the
application consists of iterating through a list
and making insertions and/or removals during the
iterations, a LinkedList will be much faster
than an ArrayList.
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Fields and implementation of the LinkedList
class There are two fields  
  private
transient int size 0    private transient
EntryltEgt header new Entry (null, null,
null)
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Fields and implementation of the LinkedList
class There are two fields  
Field not
saved if object is serialized   private
transient int size 0    private transient
Entry header new Entry (null, null,
null)
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private static class EntryltEgt E element
EntryltEgt next EntryltEgt previous Entry (ltEgt
element, EntryltEgt next, EntryltEgt previous)  
this.element element this.next
next this.previous previous //
constructor // class Entry
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public LinkedList() header.next
header.previous header For
example, ListltStringgt names new
LinkedListltStringgt()
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Empty LinkedList
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LinkedList with on element
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LinkedList with two elements
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The significance of the header entry is that
there is always an entry in back of an in front
of any entry. That simplifies insertions and
removals.
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Details of insertion into a LinkedList

• names.add (1, Don)
• The method heading for this method is
• public void add (int index, E element)
• This add method calls
• addBefore (element, entry (index))
• and the heading for addBefore is
• private EntryltEgt addBefore (E element, EntryltEgt
  e)

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• So Don will be inserted in front of the entry
  at index 1.

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Start
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Step 1 Code // insert newEntry in front of e
EntryltEgt newEntry new
Entry(element, e, e.previous)
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Step 1
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Step 2 // make newEntry follow its
predecessor newEntry.previous.next newEntry

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Step 2
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Step 3 Code // make newEntry precede its
successor, e newEntry.next.previous newEntry

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Step 3
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The same strategy works for names.add (0,
Kalena) // inserts between header entry and
entry at // index 0 names.add (names.size(),
Hana) // inserts between entry at index size()
1 // and header entry
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Group exercise Determine the output from the
following
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LinkedListltStringgt myList new
LinkedListltStringgt() myList.add ("a")
myList.add ("b") myList.add ("c")
myList.add ("d") myList.add ("e")
myList.add (2, "r") myList.remove (4)
ListIteratorltStringgt itr myList.listIterator
(3) itr.previous() itr.add ("x")
itr.next() itr.remove() itr
myList.listIterator (myList.size()) while
(itr.hasPrevious())
System.out.println (itr.previous())
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• Line editor A program that manipulates test,
  line by line.
• First line line 0
• One line is designated the current line.
• Each editing command begins with .

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protected void line (int m) if (m lt
0) throw new RuntimeException
(M_LESS_THAN_ZERO) if (m gt
text.size()) throw new
RuntimeException (M_TOO_LARGE)
current text.listIterator (m) // method line
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