Define a class named Document that contains an instance variable of type String named text that stores any textual content for the document. Create a method named toString that returns the text field...

Define a class named Document that contains an instance variable of type String
named text that stores any textual content for the document. Create a method
named toString that returns the text field and also include a method to set
this value.
Next, define a class named Email that is derived from Document and includes instance
variables for the sender , recipient , and title of an email message. Implement
appropriate accessor(get) and mutator (set) methods. For example get and set method for sender variable. The body of the email message should
be stored in the inherited variable text . Redefine the toString method to concatenate
all text fields.
Similarly, define a class named File that is derived from Document and includes a
instance variable for the pathname . The textual contents of the file should be stored
in the inherited variable text . Redefine the toString method to concatenate all
text fields.
Finally, create several sample objects of type Email and File in your main method.
Test your objects by passing them to the following subroutine that returns true if
the object contains the specified keyword in the text property.
public static boolean ContainsKeyword(Document docObject,
String keyword)
{
if (docObject.toString().indexOf(keyword,0) >= 0)
return true ;
return false ;
}