java开始到熟悉105-107

1，HashMap基本用法

package list;

import java.util.HashMap;
import java.util.Map;

/**
 * 测试map的基本用法
 * @author acer
 *
 */
public class Hashmap {
    public static void main(String[] args)
    {
        Map map=new HashMap();
        System.out.println(map.isEmpty());
        map.put("日本汽车", new car("丰田"));
        map.put("德国汽车", new car("奥迪"));
        map.put("日本电器", new camera("canon"));
        map.put("one", new Integer(1));
        System.out.println(map.size());
        car c=(car)map.get("日本汽车");
        System.out.println(c.name);
        System.out.println(map.containsKey("日本汽车"));
        System.out.println(map.containsValue(new car("canon")));
        System.out.println(map.containsValue(new Integer(1)));
        map.remove("日本");
    }
}
class car{
    String name;
    public car(String name)
    {
        this.name=name;
    }
}
class camera{
    String name;
    public camera(String name)
    {
        this.name=name;
    }
}

2.自己定义HashMap()(原始版)

package list;
/**
 * 实现较为粗糙的HashMap类
 * Map：1，存放键值对2根据键对象找相应的值对象3键值不能重复
 * @author acer
 *
 */
public class myHashMap {
    arrmap[] arr=new arrmap[100];//此时暂时不考虑数组扩容问题，只实现一些基本的方法
    int size;
    public void put(Object key,Object value)
    {
        arrmap newarr=new arrmap(key,value);
        //解决键值重复的问题
        for(int i=0;i<size;i++)
        {
            if(arr[i].key.equals(key))
            {
                arr[i].value=value;
                return;
            }
        }
        arr[size++]=newarr;
    }
    public Object get(Object key)
    {
        for(int i=0;i<size;i++)
        {
            if(arr[i].key.equals(key))
                return arr[i].value;
        }
        return null;
    }
    public boolean containsKey(Object key)
    {
        for(int i=0;i<size;i++)
        {
            if(arr[i].key.equals(key))
            {
                return true;
            }
        }
        return false;
    }
    public boolean containsValue(Object value)
    {
        for(int i=0;i<size;i++)
        {
            if(arr[i].value.equals(value))
            {
                return true;
            }
        }
        return false;
    }
    public static void main(String[] args)
    {
        myHashMap arr=new myHashMap();
        arr.put("日本", new car("丰田"));
        arr.put("德国", new car("奔驰"));
        arr.put("美国", new car("福特"));
        arr.put("日本电器", new camera("canon"));
        car c=(car)arr.get("日本");
        System.out.println(c.name);
        camera d=(camera)arr.get("日本电器");
        System.out.println(d.name);
        System.out.println(arr.containsKey("日本"));
        System.out.println(arr.containsValue(new car("丰田")));
        arr.put("日本", new car("本田"));
        c=(car)arr.get("日本");
        System.out.println(c.name);
    }
}
 class arrmap
{
    Object key;
    Object value;
    public arrmap(Object key,Object value)
    {
        this.key=key;
        this.value=value;
    }
}

3.升级版

package list;

import java.util.LinkedList;

/**
 * 完善粗糙的myhashmap
 * 提高查询效率
 * @author acer
 *
 */
public class myHashMapUpdate {
    LinkedList[] arr=new LinkedList[999];
    int size;
    public void put(Object key,Object value)
    {
        arrmap arra=new arrmap(key,value);
        int a=key.hashCode()%999;
        if(arr[a]==null)
        {
            LinkedList list=new LinkedList();
            arr[a]=list;
            list.add(arra);
        }
        else
        {
            LinkedList list=arr[a];
            for(int i=0;i<list.size();i++)
            {
                arrmap arra1=(arrmap)list.get(i);
                if(arra1.key.equals(key))
                {
                    arra1.value=value;
                    return;
                }
            }
            arr[a].add(arra);
        }
    }
    public Object get(Object key)
    {
        int a=key.hashCode()%999;
        if(arr[a]!=null)
        {
            LinkedList list=arr[a];
            for(int i=0;i<list.size();i++)
            {
                arrmap arra=(arrmap)list.get(i);
                if(arra.key.equals(key))
                {
                    return arra.value;
                }
            }
        }
        return null;
    }
    public static void main(String[] args)
    {
        myHashMapUpdate arr=new myHashMapUpdate();
        arr.put("日本", new car("丰田"));
        arr.put("日本", new car("本田"));
        arr.put("德国", new car("奔驰"));
        arr.put("美国", new car("福特"));
        arr.put("日本电器", new camera("canon"));
        car c=(car)arr.get("日本");
        System.out.println(c.name);
    }
}