Java中IdentityHashMap与HashMap区别详解

if (e.hash == hash && ((k = e.key) == key || key.equals(k))) 

 if (item == k) 

package com.scc;
import java.awt.Color;
/**
 * 双胞兄弟
 */
public class Twins
{
    /**
     * 衣服颜色
     */
    private Color color;
    public Twins(Color color)
    {
        this.color = color;
    }
    @Override
    public boolean equals(Object o)
    {
        if (o == this)
            return true;
        if (!(o instanceof Twins))
        {
            return false;
        }
        Twins user = (Twins)o;
        return color.equals(user.color);
    }
    @Override
    public int hashCode()
    {
        int result = 17;
        result = 31 * result + color.hashCode();
        return result;
    }
    public void setColor(Color color)
    {
        this.color = color;
    }
}

package com.scc;
import java.awt.Color;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Map;
public class MainTest
{
    public static void main(String[] args)
    {
        Map<Twins, String> hashMap = new HashMap<Twins, String>();
        Map<Twins, String> identityMap = new IdentityHashMap<Twins, String>();
        // 兄弟
        Twins brother = new Twins(Color.green);
        // 哥哥
        Twins eldBrother = new Twins(Color.green);
        hashMap.put(brother, "弟弟");
        hashMap.put(eldBrother, "哥哥");
        System.out.println(hashMap);//{com.scc.Twins@ff01010f=哥哥} 结果却只有哥哥
        identityMap.put(brother, "绿色衣服的弟弟");
        //第二天弟弟换了一身蓝衣服
        brother.setColor(Color.BLUE);
        identityMap.put(brother, "蓝色衣服的弟弟");
        System.out.println(identityMap);//{com.scc.Twins@ff00030e=蓝色衣服的弟弟} 结果弟弟还是弟弟,只是颜色不同罢了
    }
}