Creating an ArrayList iterator from scratch
I am having trouble understanding how iterators are supposed to be implemented in a working program. I am trying to make an ArrayList that I can iterate through and supports wrap-around. I'm not sure if the methods are one-hundred percent correct since I can't even get a working driver to test them with. Here's what I have so far.
publicinterface Iterator<E>{
publicboolean hasNext();
public E next();
publicvoid remove();
}
publicinterface ListIterator<E>extends Iterator<E>{
publicvoid add(E e);
publicboolean hasNext();
publicboolean hasPrevious();
public E next();
publicint nextIndex();
public E previous();
publicint previousIndex();
publicvoid remove();
publicvoid set(E e);
}
publicclass ArrayIterator<E>implements ListIterator<E>{
protected E[] a;
protectedint size;
protectedint cursor;
protectedint lastIndex;
public ArrayIterator(){
this.a = a;
this.size = size;
cursor = -1;
lastIndex = -1;
}
publicvoid add(E e){
thrownew UnsupportedOperationException("Size of array is fixed" );
}
publicboolean hasNext(){
return size > 0;
}
publicboolean hasPrevious(){
return size > 0;
}
public E next(){
if ( cursor == -1 || cursor == size )
cursor = 0;
lastIndex = cursor;
return a[cursor++];
}
publicint nextIndex(){
int i = lastIndex + 1;
if ( i == size )
i = 0;
return i;
}
public E previous(){
if ( cursor <= 0 )
cursor = size;
lastIndex = --cursor;
return a[cursor];
}
publicint previousIndex(){
int i = lastIndex - 1;
if ( i < 0 )
i = size - 1;
return i;
}
publicvoid remove(){
thrownew UnsupportedOperationException("Size of array is fixed" );
}
publicvoid set(E e){
a[lastIndex] = e;
}
public Iterator<E> iterator(){
returnthis;
}
}
publicclass ArrayIndexList<E>implements IndexList<E>{
private E[] A;
privateint capacity = 16;
privateint size = 0;
privateboolean usedNext =false;
public ArrayIndexList(){
A = (E[])new Object[capacity];
}
publicvoid add(int r, E e){
if (size == capacity){
capacity *= 2;
E[] B =(E[])new Object[capacity];
for (int i = 0; i < size; i++)
B[i] = A[i];
A = B;
}
for (int i = size-1; i >= r; i--)
A[i+1] = A[i];
A[r] = e;
size++;
}
public E get(int i){
return A[i];
}
publicboolean isEmpty(){
return ( size == 0 );
}
public Iterator iterator(){
returnnew ArrayIterator();
}
public E remove(int r){
E temp = A[r];
for (int i = r; i < size-1; i++)
A[i] = A[i+1];
size--;
return temp;
}
publicvoid set(int i, E e){
A[i] = e;
}
publicint size(){
return size;
}
public String toString(){
Iterator<E> it = this.iterator();
String s ="[";
while (it.hasNext()){
s += it.next();
if (it.hasNext())
s +=", ";
}
s +="]";
return s;
}
}
If someone can tell me what I'm doing wrong, or can give/link me an example of a fully functioning ArrayList iterator with all of the classes, then that'd be great. I'm sorry I can't be any more specific with what I'm stuck on. I don't know even know which questions I should be asking. :(
