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