HashMap does use equals() [was Re: DO NOT REPLY [Bug 18355] - HttpState cannot differentiate credentials for different hosts with sameRealm names]

[Mike Moran]

[EMAIL PROTECTED] wrote:
[ ... ]
The reason is because HashMap only compares the hashCodes of 
the objects and never consults equals. 

[ ... ]

This is not the case. HashMap uses equals() when the hashCode() of two 
objects are the same. If you want good performance it is a good idea to 
have the hashCode() different or at least evenly distributed. However, 
it is not necessary. As a test, try the following code:

import java.util.*;

public class HashMapThing
{
   private static class Key
   {
       private int hashCode;
       private String content;
       private String tag;
       public Key(int hashCode, String content, String tag)
       {
           this.hashCode = hashCode;
           this.content = content;
           this.tag = tag;
       }
       public int hashCode()
       {
           System.out.println("hashCode() called on " + toString());
           return hashCode;
       }
       public boolean equals(Object o)
       {
           System.out.println("equals() called on " + toString()
                              + ", " + o.toString());
           if (o instanceof Key) {
               Key other = (Key) o;
               return this.content.equals(other.content);
           }
           else {
               return false;
           }
       }
      
       public String toString()
       {
           return "tag: \"" + tag
               + "\" code: " + hashCode
               + " content: \"" + content + "\"";
       }
   }

   public static void main(String[] args) throws Exception
   {
       Key entryA = new Key(0, "0", "A");
       Key entryB = new Key(0, "0", "B");
       Key entryC = new Key(0, "1", "C");
       System.out.println("Adding entries:");
       Map map = new HashMap();
       System.out.println("A");
       map.put(entryA, "1");
       System.out.println("B");
       map.put(entryB, "2");
       System.out.println("C");
       map.put(entryC, "3");
       System.out.println("\nGetting entries:");
       String out1 = (String) map.get(entryA);
       String out2 = (String) map.get(entryC);
       System.out.println("\nEntries:");
       System.out.println("1: " + out1);
       System.out.println("2: " + out2);
   }
}
--
Mike
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