/**
 * Created by chengbx on 2018/5/17.
 * 自己實現一個ArrayList，幫助我們更好的理解ArrayList的底層結構！
 * 一句話概括ArrayList的底層：數組的擴容與數據的拷貝！
 */
public class CbxArrayList {
    //存儲集合中的元素
    private Object[] elementData;
    //容器中存儲的元素數量
    private int size;

    public  CbxArrayList(){
        this(10);
    }
    public CbxArrayList(int
 
 initialCapacity){
        if(initialCapacity < 0){
            try {
                throw new Exception();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        elementData = new Object[initialCapacity];
    }

    public void add(Object obj){
        
 
//數組擴容和數據的拷貝
        if(size+1 > elementData.length){
            Object[] newArray = new Object[size*2+1];
            System.arraycopy(elementData,0,newArray,0,elementData.length);
            elementData = newArray;
        }
        elementData[size++] = obj;
    }
    public int size(){
        
 
return  size;
    }

    public boolean isEmpty(){
        return size == 0;
    }
    public Object get(int index){

       RangeCheck(index);
       return elementData[index];
    }
    //索引校驗
    private void RangeCheck(int index){
        if(index >= size){
            try {
                throw new Exception();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    public void remove(int index){
        int numMoved = size - index - 1;
        if(numMoved > 0){
            System.arraycopy(elementData,index+1,elementData,index,numMoved);
        }
        elementData[--size] = null;

    }
    //遍歷數組 取出與其相等(equals)的數據 刪除
    public boolean remove(Object o){

        for(int i =0;i < size; i++){
            if(o.equals(elementData[i])){ //註意：底層調用的是 而不是 ==
                int numMoved = size - i - 1;
                if(numMoved > 0){
                    System.arraycopy(elementData,i+1,elementData,i,numMoved);
                }
            }
            return true;
        }
        return false;
    }
    //取出原數組索引數據 將新數據賦值到對應索引位置，返回老數據
    public Object set(int index,Object o){
        Object oldData = elementData[index];
        elementData[index] = o;
        return oldData;
    }
    public void add(int index,Object object){
        RangeCheck(index);
        System.arraycopy(elementData,index,elementData,index+1,size - index);
        elementData[index] = object;
        size++;
    }



}

ArrayList底層源碼實現練習