How does JDK implement the iterator interface?

The following code is used by enthusiastic netizens to implement the iterator interface in the form of anonymous classes:

Import Java. util. iterator; <br/> public class ourarraylist <E> implements iterable <e >{< BR/> private e [] datas; <br/> private int size; </P> <p> Public ourarraylist () {<br/> This (16); <br/>}</P> <p> @ suppresswarnings ("unchecked ") <br/> Public ourarraylist (INT capacity) {<br/> datas = (E []) New object [capacity]; <br/> size = 0; <br/>}</P> <p> @ suppresswarnings ("unchecked") <br/> Public void add (INT index, e OBJ) {<br/> If (size> = datas. length) {<br/> E [] newdata = (E []) New object [datas. length * 2 + 1]; <br/> system. arraycopy (datas, 0, newdata, 0, datas. length); <br/> datas = newdata; <br/>}</P> <p> for (INT I = size-1; I >= index; I --) <br/> datas [I + 1] = datas [I]; <br/> datas [Index] = OBJ; <br/> size ++; <br/>}</P> <p> Public e get (INT index) {<br/> If (index <size) {<br/> return (E) datas [Index]; <br/>}else <br/> return NULL; <br/>}</P> <p> Public iterator <E> iterator () {<br/> // anonymous internal class implementing the iterator interface <br/> return New iterator <E> () {<br/> int COUNT = 0; </P> <p> Public Boolean hasnext () {<br/> return count <size; <br/>}</P> <p> Public E next () {<br/> return get (count ++); <br/>}</P> <p> Public void remove () {<br/> // todo auto-generated method stub </P> <p >}</P> <p> }; <br/>}</P> <p>

In fact, JDK implements the iterator interface in this way. The following code is extracted from the javasactlist.

Private class itr implements iterator <e >{< br/>/** <br/> * index of element to be returned by subsequent call to next. <br/> */<br/> int cursor = 0; </P> <p>/** <br/> * index of element returned by most recent call to next or <br/> * previous. reset to-1 if this element is deleted by a call <br/> * to remove. <br/> */<br/> int lastret =-1; </P> <p>/** <br/> * The modcount value that the iterator bel Ieves that the backing <br/> * List shocould have. if this expectation is violated, the iterator <br/> * has detected concurrent modification. <br/> */<br/> int expectedmodcount = modcount; </P> <p> Public Boolean hasnext () {<br/> return cursor! = Size (); <br/>}</P> <p> Public E next () {<br/> checkforcomodification (); <br/> try {<br/> E next = get (cursor); <br/> lastret = cursor ++; <br/> return next; <br/>} catch (indexoutofboundsexception e) {<br/> checkforcomodification (); <br/> throw new nosuchelementexception (); <br/>}</P> <p> Public void remove () {<br/> If (lastret =-1) <br/> throw new illegalstateexception (); <br/> checkforcomod Ification (); </P> <p> try {<br/> abstractlist. this. remove (lastret); <br/> If (lastret <cursor) <br/> cursor --; <br/> lastret =-1; <br/> expectedmodcount = modcount; <br/>} catch (indexoutofboundsexception e) {<br/> throw new concurrentmodificationexception (); <br/>}</P> <p> final void checkforcomodification () {<br/> If (modcount! = Expectedmodcount) <br/> throw new concurrentmodificationexception (); <br/>}< br/>}