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