ArrayList的实现

package com.nasuf.arraylist;

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

public class MyArrayList<AnyType> implements Iterable<AnyType> {
    
    private static final int DEFAULT_CAPICITY = 10;
    
    private int theSize;
    private AnyType[] theItems;
    
    public MyArrayList() {
        clear();
    }
    
    public void clear() {
        theSize = 0;
        ensureCapacity(DEFAULT_CAPICITY);
    }
    
    public int size() {
        return theSize;
    }
    
    public boolean isEmpty() {
        return size() == 0;
    }
    
    public void trimToSize() {
        ensureCapacity(size());
    }
    
    public AnyType get(int idx) {
        if (idx < 0 || idx >= size()) 
            throw new ArrayIndexOutOfBoundsException();
        return theItems[idx];
    }
    
    public AnyType set(int idx, AnyType newVal) {
        if (idx < 0 || idx >= size()) 
            throw new ArrayIndexOutOfBoundsException();
        AnyType old = theItems[idx];
        theItems[idx] = newVal;
        return old;
    }

    public void ensureCapacity(int newCapacity) {
        if (newCapacity < theSize)
            return;
        AnyType [] old = theItems;
        theItems = (AnyType []) new Object[ newCapacity ];
        for (int i=0; i<size(); i++) {
            theItems[i] = old[i];
        }
    }
    
    public boolean add(AnyType x) {
        add(size(), x);
        return true;
    }
    
    public void add(int idx, AnyType x) {
        if (theItems.length == size()) 
            ensureCapacity(size() * 2 + 1);
        for (int i=theSize; i>idx; i--)
            theItems[i] = theItems[i=1];
        theItems[idx] = x;
        theSize ++;
    }
    
    public AnyType remove(int idx) {
        AnyType removedItem = theItems[idx];
        for(int i=idx; i<size(); i++) 
            theItems[i] = theItems[i + 1];
        theSize --;
        return removedItem;
    }

    @Override
    public Iterator<AnyType> iterator() {
        return new ArrayListIterator();
    }
    
    private class ArrayListIterator implements Iterator<AnyType> {

        private int current = 0;
        
        @Override
        public boolean hasNext() {
            return current < size();
        }

        @Override
        public AnyType next() {
            if (!hasNext()) 
                throw new NoSuchElementException();
            return theItems[current++];
        }
        
        public void remove() {
            MyArrayList.this.remove(--current);
        }
        
    }

}