Java ArrayList的底层实现方法

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));	}	 }