Implementation for custom keys in Hashtable

Question

If we implement our own keys in Hashtable, then our custom hashtable keys must implement

public int hashCode()
{
}

and

 public Object equals(Object obj)
   {
   }

What will be the implementations for these methods?

Answer 1

Read this article: http://www.ibm.com/developerworks/java/library/j-jtp05273.html

Answer 2

Read "Effective Java 2nd Edition", this is a good time for it.

HashCode and Equals method in Java object – A pragmatic concept

Java Equals Implementation

Equals and Hashcode Implementation.

Answer 3

Effective Java 2nd edition has the best explaination for these two methods: check the gory deailt here.

Answer 4

After you understood it by reading effective java, you might use commons lang EqualsBuilder and HashCodeBuilder to implement it. If the part isn't performance critical, you even can use the refelction method like this:

 public boolean equals(Object obj) {
   return EqualsBuilder.reflectionEquals(this, obj);
 }


public int hashCode() {
   return HashCodeBuilder.reflectionHashCode(this);
 }

It don't gets much easier :)

Answer 5

These methods are used for hashtable implementation to identify elements while inserting and retrieval.

1. hashcode is the key for storing
2. equals used methods contains, get etc to check the keys.