ArrayList模拟实现

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

/**
 * ArrayList模拟实现
 * 
 * @author Jelly
 * 
 * @param <T>
 */
public class MyArrayList<T> implements Iterable<T> {
	
	private static final int DEFAULE_CAPACITY = 10;
	private int theSize;
	private T[] theItems;

	public MyArrayList() {
		clear();
	}

	public void clear() {
		theSize = 0;
		ensureCapacity(DEFAULE_CAPACITY);
	}

	public int size() {
		return theSize;
	}

	public boolean isEmpty() {
		return size() == 0;
	}

	public void trimToSize() {
		ensureCapacity(size());
	}

	public T get(int idx) {
		if (idx < 0 || idx >= size()) {
			throw new ArrayIndexOutOfBoundsException();
		}
		return theItems[idx];
	}

	public T set(int idx, T newVal) {
		if (idx < 0 || idx >= size()) {
			throw new ArrayIndexOutOfBoundsException();
		}
		T old = theItems[idx];
		theItems[idx] = newVal;
		return old;
	}

	public boolean add(T t) {
		add(size(), t);
		return true;
	}

	public void add(int idx, T t) {
		if (theItems.length == size()) {
			ensureCapacity(size() * 2);
		}
		for (int i = size(); i > idx; i--) {
			theItems[i] = theItems[i - 1];
		}
		theItems[idx] = t;
		theSize++;
	}

	public T remove(int idx) {
		T t = theItems[idx];
		for (int i = idx; i < size()-1; i++) {
			theItems[i]=theItems[i+1];
		}
		theSize--;
		return t;
	}

	@SuppressWarnings("unchecked")
	public void ensureCapacity(int newCapacity) {
		if (newCapacity < DEFAULE_CAPACITY) {
			return;
		}
		T[] old = theItems;
		theItems = (T[]) new Object[newCapacity];
		for (int i = 0; i < size(); i++) {
			theItems[i] = old[i];
		}
	}

	@Override
	public Iterator<T> iterator() {
		return new ArrayListIterator();
	}

	public class ArrayListIterator implements Iterator<T> {

		private int current = 0;

		@Override
		public boolean hasNext() {
			return current < size();
		}

		@Override
		public T next() {
			if (!hasNext()) {
				throw new NoSuchElementException();
			}
			return theItems[current++];
		}

		@Override
		public void remove() {
			MyArrayList.this.remove(--current);
		}

	}
}