简单实现MyArrayList

这篇看不懂下篇看了也没有！

package cn.limbo.java_structure;

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

/**
 * MyArrayList:
 * 1:保持基础数,数组的容量以及存储在MyArrayList中当前项数
 * 2:提出一种机制用来改变基础数组的容量.获得一个新的数组,将老数组拷贝到新数组中用来改变数组的容量,允许虚拟机回收老数组
 * 3:提供get和set实现,将提供基本的类型 size isEmpty clear AND remove 和重载的add 方法可以自增容量的
 * 4:提供一个实现Iterator接口的类并且提供next hasNext remove方法的实现并且直接实现Iterator接口的该类的新构造的实例
 */
public class MyArrayList implements Iterable {

    //定义初始长度是16
    private static final int DEFAULT_CAPACITY = 10;
    private int theSize;//表示当前数组的长度
    private T[] theItems;

    public MyArrayList() {
        clear();
    }

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

    public int size() {
        return theSize;
    }

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

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

    private void ensureCapacity(int newCapacity) {
        if (newCapacity == theSize)
            return;
        T[] old = theItems;
        theItems = (T[]) new Object[newCapacity];
        for (int i = 0; i < size(); i++) {
            theItems[i] = old[i];
        }
    }

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

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

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

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

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


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

    private class ArrayListIterator implements Iterator {

        private int current = 0;

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

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

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

}