ArrayList.java

package com.coding.basic;

import java.util.Arrays;

public class ArrayList implements List {
	
	private int size = 0;
	
	private Object[] elementData = new Object[3];
	
	public void add(Object o){
		ensureCapacity(size + 1);
		elementData[size] = o;
		size++;
	}

	public void add(int index, Object o){
		if (index > size){
			throw new IndexOutOfBoundsException();
		}

		// 扩容
		ensureCapacity(size + 1);

		// 移动元素
		System.arraycopy(elementData,index,elementData,index + 1 ,size-index);
		elementData[index] = o;
		size ++ ;
	}

	private void ensureCapacity(int minCapacity) {
		int newLength = Math.max(minCapacity, size * 2);
		elementData = Arrays.copyOf(elementData, newLength);
	}

	public Object get(int index){
		checkIndex(index);
		return elementData[index];
	}
	
	public Object remove(int index){
		checkIndex(index);
		Object removed = elementData[index];
		System.arraycopy(elementData,index + 1,elementData,index,size-1 - index);
		size --;
		return removed;
	}

	private void checkIndex(int index) {
		if (index > size-1){
			throw new IndexOutOfBoundsException();
		}
	}

	public int size(){
		return size;
	}
	
	public Iterator iterator(){
		return new ArrayListIterator();
	}

	private class ArrayListIterator implements Iterator {

		private int position = 0;

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

		@Override
		public Object next() {
			Object o = get(position);
			position++ ;
			return o;
		}
	}
	
}