使用两个（或多个）对象作为HashMap键 [英] Using two (or more) objects as a HashMap key

问题描述

我想在HashMap中存储某些对象。问题是，通常你只需要使用单个对象作为关键字。 （例如，您可以使用String。）我想要使用多个对象。例如，一个Class和一个String。有没有一个简单干净的方法来实现？

I want to store certain objects in a HashMap. The problem is, usually you just use a single object as a key. (You can, for example, use a String.) What I want to do it to use multiple object. For example, a Class and a String. Is there a simple and clean way to implement that?

推荐答案

你的密钥必须实现hashCode和equals。如果它是一个 SortedMap ，它也必须实现Comparable接口

You key must implement the hashCode and equals. If it is a SortedMap, it must also implements the Comparable interface

public class MyKey implements Comparable<MyKey>
{
private Integer i;
private String s;
public MyKey(Integer i,String s)
{
this.i=i;
this.s=s;
}

public Integer getI() { return i;}
public String getS() { return s;}

@Override
public int hashcode()
{
return i.hashcode()+31*s.hashcode();
}

@Override
public boolean equals(Object o)
{
if(o==this) return true;
if(o==null || !(o instanceof MyKey)) return false;
MyKey cp= MyKey.class.cast(o);
return i.equals(cp.i) && s.equals(cp.s);
    }

   public int compareTo(MyKey cp)
     {
     if(cp==this) return 0;
     int i= i.compareTo(cp.i);
     if(i!=0) return i;
     return s.compareTo(cp.s);
     }


 @Override
    public String toString()
       {
       return "("+i+";"+s+")";
       }

    }

public Map<MyKey,String> map= new HashMap<MyKey,String>();
map.put(new MyKey(1,"Hello"),"world");

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