Need for Iterators 7 2 T getint at

Iterable<T> {interface} Iterable + Iterator<T> iterator(); My. List<T> {interface} (see the java document) ….

Iterator<T> {interface} API java. util. Iterator<E> head 0 + boolean has. Next(); + T

my. Iterator inner class package my. Util; import java. util. Iterator; import java. util.

my. Iterator (countined) /*****This is an inner class for my. Iterator ******/ public class

public Iterator<T> iterator() { return new my. Iterator(); } internal class Anonymous Class public

A Marker Interface static <T extends Random. Access> void swap(T x, int i, int

Single Linked List It is very common to add new items to the end

API java. util. List. Iterator<T> Tail doesn’t help tail head 0 1 2 3

API java. util. List. Iterator<E> head tail 0 1 2 3 4 next. Node

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Need for Iterators 7 2 T get(int at) 6 1 for (int i=0; i< L. size(); i++) {. . L. get(i). . . } 8 We cannot improve this, because the internal information and structures are protected. But, 1+2+3+. . . +n = (1+n)*n/2 O(n 2) 9/9/2020 3 5 this is a common application Suppose L. size() = n O(n) ? 4 IT 179 1

Iterable<T> {interface} Iterable + Iterator<T> iterator(); My. List<T> {interface} (see the java document) …. package my. Util; import java. util. Iterator; import java. util. No. Such. Element. Exception; public class My. SLinked. List <T> implements My. List<T>{ {. . . . public Iterator<T> iterator() { return new my. Iterator(); }. . . } 9/9/2020 Another inner class that defines our iterator. IT 179 2

Iterator<T> {interface} API java. util. Iterator<E> head 0 + boolean has. Next(); + T next(); + void remove(); 1 2 3 next. Node 4 5 6 Point to the node that will be returned by next call of next() seen. Node Point to the node that is seen (may be removed later) prev. Node 9/9/2020 Point to the node before the seen node. IT 179 3

my. Iterator inner class package my. Util; import java. util. Iterator; import java. util. No. Such. Element. Exception; public class My. SLinked. List<T> implements My. List<T>, Iterable<T>{. . /***** This is an inner class for my. Iterator ******/ public class my. Iterator implements Iterator<T> { private Node<T> prev. Node=null, seen. Node=null, next. Node=head; // current node to be seen //by next() public boolean has. Next() { return (next. Node != null); } … … } /***** This is the end of inner class my. Iterator ******/ 9/9/2020 IT 179 4

my. Iterator (countined) /*****This is an inner class for my. Iterator ******/ public class my. Iterator implements Iterator<T> {. . . . public T next() { if (! has. Next()) throw new No. Such. Element. Exception("No. Such. Element. Exception: "); if (seen. Node != null) // The seen node is not removed prev. Node = seen. Node; seen. Node = next. Node; next. Node = next. Node. next; return seen. Node. data; }. . . . /***** This is the end of inner class my. Iterator ******/ 9/9/2020 IT 179 5

my. Iterator (countined) /*****This is an inner class for my. Iterator ******/ public class my. Iterator implements Iterator<T> {. . . . public void remove() { if (seen. Node == null) throw new Illegal. State. Exception("Illegal. State. Exception: "); if (seen. Node == head) { head = seen. Node. next; } else { prev. Node. next = next. Node; } seen. Node = null; // it's gone size--; }. . . . } /***** This is the end of inner class my. Iterator ******/ 9/9/2020 IT 179 6

public Iterator<T> iterator() { return new my. Iterator(); } internal class Anonymous Class public Iterator<T> iterator() { return new Iterator<T>() { /* Return an Anonymous class as an iterator ***/ …… /* same as the body the my. Iterator */ …… /* This is the end of the Anonymous class *****/ }; /** don't forget "; " **/ } /* end of iterator */ 9/9/2020 IT 179 7

A Marker Interface static <T extends Random. Access> void swap(T x, int i, int j) { if (!(x instanceof List)) return; T temp = x. get(i); x. set(i, x. get(j)); x. set(j, temp); } public static void main(String[] args) { Array. List<Object> A = new Array. List<Object>(); Linked. List<Object> B = new Linked. List<Object>(); List<Object> C; . . . swap(A, 30, 95); swap(B, 30, 95); C = B swap(C, 30, 95); } 9/9/2020 IT 179 8

Single Linked List It is very common to add new items to the end of the list public void add(T item) { // append item to the end of the list add(size, item); } Easy Solution: tail head 52 Can Iterator help? No! 12 14 16 23 for (int i=0; i<n; i++) { something =. . . list. add(something); } 9/9/2020 45 1+2+3+. . . +n = (1+n)*n/2 O(n 2) Add to the tail (append) IT 179 48 9

API java. util. List. Iterator<T> Tail doesn’t help tail head 0 1 2 3 4 next. Node List. Iterator<T> {interface} + + + + + boolean has. Next(); boolean has. Previous(); T next(); T previous(); void remove(); int next. Index() int previous. Index(); void add(T item); void set(T item); Point to the node that will be returned by next call of next() seen. Node Point to the node that is seen (may be removed later) prev. Node 9/9/2020 Point to the node before the seen node. IT 179 10

API java. util. List. Iterator<E> head tail 0 1 2 3 4 next. Node List. Iterator<T> {interface} + + + + + boolean has. Next(); boolean has. Previous(); T next(); T previous(); void remove(); int next. Index() int previous. Index(); void add(T item); void set(T item); Point to the node that will be returned by next call of next() seen. Node Point to the node that is seen (may be removed later) 9/9/2020 IT 179 13