Add equals() and hashCode() implementations that allow a Tuple to be used

as a HashMap key.


git-svn-id: https://samskivert.googlecode.com/svn/trunk@470 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/util/Tuple.java

@@ -1,5 +1,5 @@
 //
-// $Id: Tuple.java,v 1.2 2001/08/11 22:43:29 mdb Exp $
+// $Id: Tuple.java,v 1.3 2001/11/26 19:22:12 mdb Exp $
 //
 // samskivert library - useful routines for java programs
 // Copyright (C) 2001 Michael Bayne
@@ -22,6 +22,8 @@ package com.samskivert.util;
 
 /**
  * A tuple is a simple object that holds a reference to two other objects.
+ * It provides hashcode and equality semantics that allow it to be used to
+ * combine two objects into a single key (for hashtables, etc.).
  */
 public class Tuple
 {
@@ -43,6 +45,32 @@ public class Tuple
     {
     }
 
+    /**
+     * Returns the combined hashcode of the two elements.
+     */
+    public int hashCode ()
+    {
+        return left.hashCode() ^ right.hashCode();
+    }
+
+    /**
+     * A tuple is equal to another tuple if the left and right elements
+     * are equal to the left and right elements (respectively) of the
+     * other tuple.
+     */
+    public boolean equals (Object other)
+    {
+        if (other instanceof Tuple) {
+            Tuple to = (Tuple)other;
+            return (left.equals(to.left) && right.equals(to.right));
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * Generates a string representation of this tuple.
+     */
     public String toString ()
     {
         return "[left=" + left + ", right=" + right + "]";