java开始到熟悉100-102

本次内容：arraylist（）

1、

 package list;

 import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;

 /**
  * 测试list的基本方法
  * @author acer
  *
  */
 public class arraylist {
     public static void main(String[] args)
     {
         List list=new ArrayList();
         //Arraylist():低层实现是数组，查找容易，插入删除复杂。线程不安全
         //LinkedList()：低层实现是链表，查找复杂，插入删除容易。线程不安全
         //Vector（）：低层实现是数组，线程安全
         list.add("aaa");
         list.add(new Date());
         list.add(1234);//包装类：自动装箱
         System.out.println(list.size());
         list.remove(0);
         System.out.println(list.size());
         list.get(0);
         System.out.println(list.get(0));
         list.set(0, "bbb");
         System.out.println(list.get(0));
         System.out.println(list.get(1));
     }
 }

运行结果：
3
2
Tue May 20 22:18:58 CST 2014
bbb
1234

2、自己定义arraylist（）函数

 package list;

 import java.util.Date;

 /**
  * 自己定义arraylist，熟悉其低层实现
  * @author acer
  *
  */
 public class myarraylist {
     private Object[] elementData;
     private int size;
     public int size()//数组的大小
     {
         return size;
     }
     public myarraylist(int initalCapacity)//构造器
     {
         elementData=new Object[initalCapacity];
     }
     public Object get(int index)//取数组的值
     {
         rangeCheck(index);
         return elementData[index];
     }
     public void add(Object object)//添加对象
     {
         ensureCapacity();
         elementData[size++]=object;
     }
     public void add(int index,Object obj)//指定位置添加对象
     {
         rangeCheck(index);
         ensureCapacity();
         int numMoved=size-index;
         System.arraycopy(elementData, index, elementData, index+1, numMoved);
         elementData[index]=obj;
         size++;

     }
     private void ensureCapacity()//数组的扩容
     {
         if(size==elementData.length)
         {
             Object[] newarraylist=new Object[size*2+1];
             System.arraycopy(elementData, 0,newarraylist,0,elementData.length);
             elementData=newarraylist;
         }
     }
     public void remove(int index)//移除对象
     {
         rangeCheck(index);
         int numMoved=size-index-1;
         if(numMoved>0)
         {
             System.arraycopy(elementData, index+1, elementData, index, numMoved);
         }
         elementData[--size]=null;
     }
     public void remove(Object obj)//移除对象
     {
         for(int i=0;i<size;i++)
         {
             if(get(i).equals(obj))
             {
                 remove(i);
             }
         }
     }
     public boolean isEmpty()//判是否为空
     {
         return size==0;
     }
     private void rangeCheck(int index)//检测检索值是否越界
     {
         if(index<0||index>=size)
         {
             try {
                 throw new Exception();
             } catch (Exception e) {
                 e.printStackTrace();
             }
         }
     }
     public static void main(String[] args)
     {
         myarraylist list=new myarraylist(3);
         list.add("aaa");
         list.add("bbb");
         list.add(new Date());
         System.out.println(list.isEmpty());
         System.out.println(list.size());
         System.out.println(list.get(0));
         System.out.println(list.get(1));
         System.out.println(list.get(2));
         list.remove(0);
         list.remove(new Date());
         System.out.println(list.get(0));
         list.add(1, "aaa");
         System.out.println(list.get(1));
     }
 }

运行结果：

false
3
aaa
bbb
Tue May 20 23:41:15 CST 2014
bbb
aaa