本次内容：arraylist（）

1、

1 package list; 2  3 import java.util.ArrayList; 4 import java.util.Date; 5 import java.util.List; 6  7 /** 8  * 测试list的基本方法 9  * @author acer10  *11  */12 public class arraylist {13     public static void main(String[] args)14     {15         List list=new ArrayList();16         //Arraylist():低层实现是数组，查找容易，插入删除复杂。线程不安全17         //LinkedList()：低层实现是链表，查找复杂，插入删除容易。线程不安全18         //Vector（）：低层实现是数组，线程安全19         list.add("aaa");20         list.add(new Date());21         list.add(1234);//包装类：自动装箱22         System.out.println(list.size());23         list.remove(0);24         System.out.println(list.size());25         list.get(0);26         System.out.println(list.get(0));27         list.set(0, "bbb");28         System.out.println(list.get(0));29         System.out.println(list.get(1));30     }31 }

运行结果：

3

2

Tue May 20 22:18:58 CST 2014

bbb

1234

 

2、自己定义arraylist（）函数

 

1 package list;  2   3 import java.util.Date;  4   5 /**  6  * 自己定义arraylist，熟悉其低层实现  7  * @author acer  8  *  9  */ 10 public class myarraylist { 11     private Object[] elementData; 12     private int size; 13     public int size()//数组的大小 14     { 15         return size; 16     } 17     public myarraylist(int initalCapacity)//构造器 18     { 19         elementData=new Object[initalCapacity]; 20     } 21     public Object get(int index)//取数组的值 22     { 23         rangeCheck(index); 24         return elementData[index]; 25     } 26     public void add(Object object)//添加对象 27     { 28         ensureCapacity(); 29         elementData[size++]=object; 30     } 31     public void add(int index,Object obj)//指定位置添加对象 32     { 33         rangeCheck(index); 34         ensureCapacity(); 35         int numMoved=size-index; 36         System.arraycopy(elementData, index, elementData, index+1, numMoved); 37         elementData[index]=obj; 38         size++; 39          40     } 41     private void ensureCapacity()//数组的扩容 42     { 43         if(size==elementData.length) 44         { 45             Object[] newarraylist=new Object[size*2+1]; 46             System.arraycopy(elementData, 0,newarraylist,0,elementData.length); 47             elementData=newarraylist; 48         } 49     } 50     public void remove(int index)//移除对象 51     { 52         rangeCheck(index); 53         int numMoved=size-index-1; 54         if(numMoved>0) 55         { 56             System.arraycopy(elementData, index+1, elementData, index, numMoved); 57         } 58         elementData[--size]=null; 59     } 60     public void remove(Object obj)//移除对象 61     { 62         for(int i=0;i
     
      =size) 77         { 78             try { 79                 throw new Exception(); 80             } catch (Exception e) { 81                 e.printStackTrace(); 82             } 83         } 84     } 85     public static void main(String[] args) 86     { 87         myarraylist list=new myarraylist(3); 88         list.add("aaa"); 89         list.add("bbb"); 90         list.add(new Date()); 91         System.out.println(list.isEmpty()); 92         System.out.println(list.size()); 93         System.out.println(list.get(0)); 94         System.out.println(list.get(1)); 95         System.out.println(list.get(2)); 96         list.remove(0); 97         list.remove(new Date()); 98         System.out.println(list.get(0)); 99         list.add(1, "aaa");100         System.out.println(list.get(1));101     }102 }
     

运行结果：

false

3

aaa

bbb

Tue May 20 23:41:15 CST 2014

bbb

aaa