The need to provide equals with an Object parameter

Many Java books do not teach that a class should provide ability to find out whether two objects have the same value.
If a book mention equals, often it will declared with a parameter of type Date:
```
public boolean equals(final Date pDate)
{
   return iYear==pDate.iYear && iMonth==pDate.iMonth && iDay==pDate.iDay;
}
```
If a client attempts to add objects of this class to an object of the Collections API (or Hashtable or Vector), they are in for a shock ...

None of the following methods will work:

`Hashtable`	`contains`, `containsKey`, `get`, `put`, `remove`
`Vector`	`contains`, `indexOf`
`List`	`contains`, `remove`, `indexOf`
`Map`	`containsKey`, `containsValue`, `get`, `put`, `remove`
`Set`	`add`, `contains`, `remove`