【17期】什么情况用ArrayList or LinkedList呢?

public boolean add(E e){
   ensureCapacity(size+1);//确保内部数组有足够的空间
   elementData[size++]=e;//将元素加入到数组的末尾，完成添加
   return true;      
} 

public vod ensureCapacity(int minCapacity){
  modCount++;
  int oldCapacity=elementData.length;
  if(minCapacity>oldCapacity){    //如果数组容量不足，进行扩容
      Object[] oldData=elementData;
      int newCapacity=(oldCapacity*3)/2+1;  //扩容到原始容量的1.5倍
      if(newCapacitty<minCapacity)   //如果新容量小于最小需要的容量，则使用最小
                                                    //需要的容量大小
         newCapacity=minCapacity ;  //进行扩容的数组复制
         elementData=Arrays.copyof(elementData,newCapacity);
  }
}

public boolean add(E e){
   addBefore(e,header);//将元素增加到header的前面
   return true;
}

private Entry<E> addBefore(E e,Entry<E> entry){
     Entry<E> newEntry = new Entry<E>(e,entry,entry.previous);
     newEntry.provious.next=newEntry;
     newEntry.next.previous=newEntry;
     size++;
     modCount++;
     return newEntry;
}

public void add(int index,E element){
   if(index>size||index<0)
      throw new IndexOutOfBoundsException(
        "Index:"+index+",size: "+size);
         ensureCapacity(size+1);
         System.arraycopy(elementData,index,elementData,index+1,size-index);
         elementData[index] = element;
         size++;
}

public void add(int index,E element){
   addBefore(element,(index==size?header:entry(index)));
}

public E remove(int index);

public E remove(int index){
   RangeCheck(index);
   modCount++;
   E oldValue=(E) elementData[index];
  int numMoved=size-index-1;
  if(numMoved>0)
     System.arraycopy(elementData,index+1,elementData,index,numMoved);
     elementData[--size]=null;
     return oldValue;
}

public E remove(int index){
  return remove(entry(index));         
}
private Entry<E> entry(int index){
  if(index<0 || index>=size)
      throw new IndexOutBoundsException("Index:"+index+",size:"+size);
      Entry<E> e= header;
      if(index<(size>>1)){//要删除的元素位于前半段
         for(int i=0;i<=index;i++)
             e=e.next;
     }else{
         for(int i=size;i>index;i--)
             e=e.previous;
     }
         return e;
}

public  ArrayList(){
  this(10);  
}
public ArrayList (int initialCapacity){
   super();
   if(initialCapacity<0)
       throw new IllegalArgumentException("Illegal Capacity:"+initialCapacity)
      this.elementData=new Object[initialCapacity];
}

public ArrayList(int initialCapacity) 

String tmp;
long start=System.currentTimeMills();    //ForEach 
for(String s:list){
    tmp=s;
}
System.out.println("foreach spend:"+(System.currentTimeMills()-start));
start = System.currentTimeMills();
for(Iterator<String> it=list.iterator();it.hasNext();){    
   tmp=it.next();
}
System.out.println("Iterator spend;"+(System.currentTimeMills()-start));
start=System.currentTimeMills();
int size=;list.size();
for(int i=0;i<size;i++){                     
    tmp=list.get(i);
}
System.out.println("for spend;"+(System.currentTimeMills()-start));