三 模拟实现顺序表ArrayList

/**
 * 顺序表，重点是数组动态扩容，插入
 * 底层采用数组，长度可以动态变化,此处采用增长一倍，而java.util.ArrayList每次增长50%
 *  int newCapacity = oldCapacity + (oldCapacity >> 1);
 *
 */
public class ArrayList implements List{
     private Object[] elementData;//底层数组
     private int size;//元素个数

     public ArrayList(int initialCapacity) {
        //给数组分配指定数量空间
         elementData = new Object[initialCapacity];
        //指定顺序表元素个数，默认是0
        //size = 0;
     }

     public ArrayList() {
       //没有指定长度，默认initialCapacity是4
         this(4);
      //没有指定长度，长度是0
//         elementData = new Object[]{};
     }

    @Override
    public int size() {
        // TODO Auto-generated method stub
        return size;
    }

    @Override
    public Object get(int i) {
        if(i<0||i>size-1){
            throw new RuntimeException("数组指针越界:"+i);
        }
        return elementData[i];
    }

    @Override
    public boolean isEmpty() {
        // TODO Auto-generated method stub
        return size == 0;
    }

    @Override
    public boolean contains(Object e) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public int indexOf(Object e) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public void add(int i, Object e) {
        if(i<0||i>size){
            throw new RuntimeException("数组指针越界异常:"+i);
        }
       if(size == elementData.length)
        {
            grow();
        }
        for(int j =size ; j>i  ; j--){
            elementData[j] = elementData[j-1];
        }
        elementData[i] = e;
        size++;

    }

    @Override
    public void add(Object e) {

        this.add(size, e);
//    //动态扩容
//    if(size == elementData.length)
//    {
//        grow();
//    }     //        elementData[size] = e;
//        size++;
//        //System.out.println("length="+elementData.length);
    }

    public void grow(){
//        Object[] newArr = new Object[size*2];
//        for(int i = 0; i<size;i++){
//            newArr[i] = elementData[i];
//        }
//        elementData = newArr;
    elementData = Arrays.copyOf(elementData, elementData.length*2);
    }
}