CSE 3302Lecture'17:'Control28'Oct'2010Nate'NystromUniversity'of'Texas'at'ArlingtonFor loopsPascal:for$x$:=$1$to$10$do$$$$writeln(x)C:for$(x$=$1;$x$<$10;$x++)$$$$printf(“%d\n”,$x);2IterationList<String>$counting$=$$$$Arrays.asList(“yan”,$“tan”,$“tethera”,$“methera”,$“pip”);for$(int$i$=$0;$i$<$counting.size();$i++)${$$$$String$s$=$counting.get(i);$$$$println(s);}3Java iteratorsList<String>$counting$=$$$$Arrays.asList(“yan”,$“tan”,$“tethera”,$“methera”,$“pip”);for$(String$s$:$counting)${$$$$println(s);}4Java iteratorsList<String>$counting$=$$$$Arrays.asList(“yan”,$“tan”,$“tethera”,$“methera”,$“pip”);for$(String$s$:$counting)${$$$$println(s);}shorthand'for:for$(Iterator<String>$i$=$counting.iterator();$i.hasNext();$)${$$$$String$s$=$i.next();$$$$println(s);}5Java iteratorsUsing'iterators'is'easy.How'about'wriGng'one?6Writing a Java iteratorImplement'java.util.Iterator:interface$Iterator<T>${$$$$boolean$hasNext();$$$$T$next();$$$$void$remove();$$//$we’ll$ignore$this$one!}7Writing a Java iteratorclass$ArrayListIterator<T>$implements$Iterator<T>${$$$$ArrayList<T>$list;$$$$int$pos$=$0;$$$$boolean$hasNext()${$return$pos$<$list.size();$}$$$$T$next()${$$$$$$$$if$(pos$<$list.size())${$$$$$$$$$$$$pos++;$$$$$$$$$$$$return$list.get(posU1);$$$$$$$$}$$$$$$$$else$throw$new$NoSuchElementException();$$$$}}8Writing a Java iteratorclass%TreeIterator<T>%implements%Iterator<T>%{%%%%Stack<TreeNode<T>>%stack;%%%%TreeIterator(TreeSet<T>%tree)%{%%%%%%%%stack%=%new%Stack<TreeNode<T>>();%%%%%%%%pushLeft(tree.root);%%%%}%%%%void%pushLeft(TreeNode<T>%n)%{%%%%%%%%if%(n%!=%null)%stack.push(n);%%%%%%%%pushLeft(n.left);%%%%}%%%%boolean%hasNext()%{%return%!%stack.isEmpty();%}%%%%T%next()%{%%%%%%%%if%(stack.isEmpty())%throw%new%NoSuchElementException();%%%%%%%%TreeNode<T>%x%=%stack.pop();%%%%%%%%pushLeft(x.right);%%%%%%%%return%x.value;%%%%}}9class%TreeSet<T>%{%%%%%TreeNode<T>%root;%%%%%class%TreeNode<T>%{%%%%%%%%%TreeNode<T>%left,%right;%%%%%%%%%T%value;%%%%%}}Writing a Java iteratorIterator'needs'to'maintain'state◾what'have'I'already'returned?◾what'do'I'return'when'next'invoked?10Hashtable'iteratorWhat'bucket'am'I'currently'in?Where'in'the'bucket'am'I?11A better wayJust'write'a'traversal'of'the'data'structure.At'each'element'and'yield'back'to'the'iterator.12Coroutine iteratorsclass$ArrayList<T>${$$$$T[]$array;$$$$elements()$iterates$T${$$$$$$$$for$(int$i$=$0;$i$<$size;$i++)${$$$$$$$$$$$$yield$array[i];$$$$$$$$}$$$$}}for$(T$x$:$list.elements())${$$$$println(x);}13Syntax'is'Java'with'a'hypoth e1cal'extension'that'adds'a'yield'statement.class$ArrayList<T>${$$$$T[]$array;$$$$elements()$iterates$T${$$$$$$$$for$(int$i$=$0;$i$<$size;$i++)${$$$$$$$$$$$$yield$array[i];$$$$$$$$}$$$$}}for$(T$x$:$list.elements())${$$$$println(x);}yield'suspends'the'elements(),'returns'control'back'to'the'caller.When'iterator'nex
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