Java ArrayList的底层实现

package com.soto.collection;

/**
 * 自己实现一个ArrayList,帮助我们更好地理解ArrayList的底层结构;
 * @author 王
 *
 */
public class SxtArrayList {
	private Object[] elementData;
	private int size;
	public int size(){
		return size;
	}
	public boolean isEmpty(){
		return size == 0;
	}
	
	
	public  SxtArrayList(){
		this(10);
	}
	public SxtArrayList(int initialCapacity){
		if(initialCapacity<0){
			try {
				throw new Exception();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		elementData = new Object[initialCapacity];  //初始化 容量为10 
			
		
	}
	public void add(Object obj){
		elementData[size++] = obj;   //若超过容量了，那么..数组扩容
		if(size==elementData.length){
			//实质：搞个新数组
			Object[] newarray = new Object[size*2+1];
			//数组的copy:
			System.arraycopy(elementData, 0, newarray, 0, elementData.length);
			elementData = newarray;
			
		}
		
	}
	public Object get(int index){
		rangeCheck(index);
		return elementData[index];
	}
	public void remove(int index){  
		rangeCheck(index);
		
		 //删除指定位置对象，删除某位置，相当于 将后往前挪:
		int numMoved = size-index-1;
		if(numMoved>0){
			System.arraycopy(elementData, index+1, elementData, index, numMoved);
		}
	}
	public void remove(Object obj){
		for(int i=0;i<size;i++){
			if(get(i).equals(obj)){   //注意底层调用的equals方法而不是==。
				remove(i);
			}
		}
	}
	
	
	
	private void rangeCheck(int index){
		if(index<0||index>size){
			try {
				throw new Exception();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		
		
	}
	public Object set(int index, Object obj){
		rangeCheck(index);
        Object oldValue = elementData[index];
        elementData[index] = obj;
        return oldValue;
	
	}
	public void add(int index, Object obj){
		rangeCheck(index);
		ensureCapacity(); //扩容
		System.arraycopy(elementData, index, elementData, index + 1,
                size - index);
		elementData[index] = obj;
		size++;
		
	}
	private void ensureCapacity(){
		//扩容
				if(size==elementData.length){
					//实质：搞个新数组
					Object[] newarray = new Object[size*2+1];
					//数组的copy:
					System.arraycopy(elementData, 0, newarray, 0, elementData.length);
					elementData = newarray;	
				}
	}
	
	public static void main(String[] args) {
		SxtArrayList list = new SxtArrayList(3);
		list.add("222");
		list.add("333");
		list.add("444");
		list.add("555");
		list.add("666");
		list.add("777");
		System.out.println(list.size());
		System.out.println(list.get(6));
	}
	

}