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  • ArrayList底层源码实现练习

    /**
     * Created by chengbx on 2018/5/17.
     * 自己实现一个ArrayList,帮助我们更好的理解ArrayList的底层结构!
     * 一句话概括ArrayList的底层:数组的扩容与数据的拷贝!
     */
    public class CbxArrayList {
        //存储集合中的元素
        private Object[] elementData;
        //容器中存储的元素数量
        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){
            //数组扩容和数据的拷贝
            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];
        }
        //索引校验
        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;
    
        }
        //遍历数组 取出与其相等(equals)的数据 删除
        public boolean remove(Object o){
    
            for(int i =0;i < size; i++){
                if(o.equals(elementData[i])){ //注意:底层调用的是 而不是 ==
                    int numMoved = size - i - 1;
                    if(numMoved > 0){
                        System.arraycopy(elementData,i+1,elementData,i,numMoved);
                    }
                }
                return true;
            }
            return false;
        }
        //取出原数组索引数据 将新数据赋值到对应索引位置,返回老数据
        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++;
        }
    
    
    
    }
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  • 原文地址:https://www.cnblogs.com/cbxBlog/p/9126099.html
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