Java-数据结构-ArrayList

import java.util.Iterator;
import java.util.NoSuchElementException;

public class ArrayList<E> implements Iterable<E> {
    private final int INITIAL_CAPACITY = 50;
    private int count;
    private E[] data;

    public ArrayList() {
        count = 0;
        data = (E[]) new Object[INITIAL_CAPACITY];
    }

    public Iterator<E> iterator() {
        return new ArrayListIterator<E>(this);
    }

    private class ArrayListIterator<E> implements Iterator<E> {
        // fields to store state
        private ArrayList<E> list;// reference to the list it is iterating down
        private int nextIndex = 0; // the index of the next value to return
        private boolean canRemove = false;

        private ArrayListIterator(ArrayList<E> list) {
            this.list = list;
        }

        public boolean hasNext() {
            return (nextIndex < list.count);
        }

        public E next() {
            if (nextIndex >= list.count) throw new NoSuchElementException();
            canRemove = true;               //← for the remove method
            return list.get(nextIndex++);   //← increment and return
        }

        public void remove() {
            if (!canRemove) throw new IllegalStateException();
            canRemove = false;
            nextIndex--;
            list.remove(nextIndex);
        }
    }

    public E get(int index) {
        return data[index];
    }

    public void add(E item) {
        data[count++] = item;
    }

    public void remove(int index) {
        for (int i = index; i < count; i++)
            data[i] = data[i + 1];
        data[--count] = null;
    }

    public void remove() {
        remove(count - 1);
    }

}