java开始到熟悉100-102

   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 acer

10  *

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;i++)

 63         {

 64             if(get(i).equals(obj))

 65             {

 66                 remove(i);

 67             }

 68         }

 69     }

 70     public boolean isEmpty()//判是否为空

 71     {

 72         return size==0;

 73     }

 74     private void rangeCheck(int index)//检测检索值是否越界

 75     {

 76         if(index<0||index>=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