Linked lists - Data Structures and Problem Solving Using Java - page 645

36 public void remove( )
37 {
38 if( expectedModCount != modCount )
39 throw new ConcurrentModificationException( );
40 if( lastVisited == null )
41 throw new IllegalStateException( );
42
43 LinkedList.this.remove( lastVisited );
44 lastVisited = null;
45 if( lastMoveWasPrev )
46 current = current.next;
47 expectedModCount++;
48 }
49
50 public boolean hasPrevious( )
51 {
52 if( expectedModCount != modCount )
53 throw new ConcurrentModificationException( );
54 return current != beginMarker.next;
55 }
56
57 public AnyType previous( )
58 {
59 if( !hasPrevious( ) )
60 throw new NoSuchElementException( );
61
62 current = current.prev;
63 lastVisited = current;
64 lastMoveWasPrev = true;
65 return current.data;
66 }
67 }

figure 17.30b
Iterator inner class
implementation for
standard LinkedList
class ( continued )

remove . If lastVisited is null , the remove is illegal. Finally, lastMoveWasPrev is
true if the last movement of the iterator prior to remove was via previous ; it is
false if the last movement was via next .
The hasNext and hasPrevious methods are fairly routine. Both throw an
exception if an external modification to the list has been detected.
The next method advances current (line 32) after getting the value in the
node (line 30) that is to be returned (line 34). Data fields lastVisited and
lastMoveWasPrev are updated at lines 31 and 33, respectively. The implemen-
tation of previous is not exactly symmetric, because for previous , we
advance current prior to obtaining the value. This is evident when one con-
siders that the initial state for backwards iteration is that current is at the
endmarker.