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.
In Java, this is normally done by providing a method called equals.

Here is a typical call of equals:

final Date tTodaysDate = new Date(2000, 12, 25);
final Date tNoelDate = new Date(2000, 12, 25);
final boolean tIsChristmasDay = tTodaysDate.equals(tNoelDate);

If a book mentions equals, often it will be 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`, `indexOf`, `remove`
`Map`	`containsKey`, `containsValue`, `get`, `put`, `remove`
`Set`	`add`, `contains`, `remove`

For these methods to work, equals requires a parameter of type Object.