102.自己实现ArrayList

1 package collection;
  2 
  3 import java.util.ArrayList;
  4 import java.util.List;
  5 
  6 /**
  7  * 自己实现一个ArrayList，帮助理解底层结构
  8  * @author Nicholas
  9  *
 10  */
 11 public class SxArrayList{
 12     private Object[] elementData;
 13     private int size;
 14     
 15     public int size(){
 16         return size;
 17     }
 18     public SxArrayList(){
 19         this(10);//默认长度为10
 20         
 21     }
 22     
 23     public SxArrayList(int initialCapacity){
 24         if(initialCapacity<0){
 25             try {
 26                 throw new Exception();
 27             } catch (Exception e) {
 28                 e.printStackTrace();
 29             }
 30         }
 31         elementData = new Object[initialCapacity];
 32     }
 33     
 34     public boolean isEmpty(){
 35         return size==0;
 36     }
 37     
 38     public void add(Object obj){
 39         //数组扩容和数据的拷贝
 40         ensureCapacity();
 41         elementData[size++] = obj;
 42     }
 43     
 44     public Object get(int index){
 45         rangeCheck(index);
 46         return elementData[index];
 47     }
 48     
 49     public void remove(int index){
 50         rangeCheck(index);
 51         //删除指定位置的对象
 52         int numMoved = size-index-1;
 53         if(numMoved>0){
 54             System.arraycopy(elementData, index+1, elementData, size, numMoved);;
 55         }
 56         elementData[--size] = null;
 57     }
 58     
 59     public void remove(Object obj){
 60         for(int i=0;i<size;i++){
 61             if(get(i).equals(obj)){//调用的是equals不是==
 62                 remove(obj);
 63             }
 64         }
 65     }
 66     
 67     private void rangeCheck(int index){
 68         if(size<0||index>=size){
 69             try {
 70                 throw new Exception();
 71             } catch (Exception e) {
 72                 e.printStackTrace();
 73             }
 74         }
 75     }
 76     
 77     public Object set(int index,Object obj){
 78         rangeCheck(index);
 79         Object oldValue = elementData[index];
 80         elementData[index] = obj;
 81         return oldValue;
 82     }
 83     
 84     public void add(int index,Object obj){
 85         rangeCheck(index);
 86         ensureCapacity();
 87         System.arraycopy(elementData, index, elementData, index+1, size-index);
 88         elementData[index] = obj;
 89         size++;
 90     }
 91     
 92     private void ensureCapacity(){
 93         if(size == elementData.length){
 94             Object[] newArray = new Object[size*2+1];
 95             System.arraycopy(elementData, 0, newArray, 0, elementData.length);
 96             elementData = newArray;
 97         }
 98     }
 99     
100     public static void main(String[] args) {
101         SxArrayList list = new  SxArrayList(3);
102         list.add("3333");
103         list.add("4444");
104         list.add("1111");
105         list.add("2222");
106         System.err.println(list.size);
107         System.err.println(list.get(3));
108     }
109     
110 }