A good answer might be:

  • Is a String an Object?
    • Yes
  • Is a Card an Object?
    • Yes
  • Is a Applet an Object?
    • Yes

Arrays of Object

Since every class is a descendant of Object, an Object reference variable can be used with an object of any class. For example: 

Object obj;

String        str = "Yertle" ;
Double        dbl = new Double( 32.0 );
YouthBirthday ybd = new YouthBirthday( "Ian", 4 );

obj = str;
obj = dbl;
obj = ybd;

Each of the last three statements is correct (although in this program, useless.) It would not be correct if this followed the above statements: 

obj.greeting();
It is true that obj refers to a YouthBirthday object, which has a greeting() method. But the compiler needs to be told this with a type cast. The following is OK: 
((YouthBirthday)obj).greeting();
A typecast is used to tell the compiler what is "really" in a variable that itself is not specific enough.To avoid such complications, always use reference variables that are as specific as possible.

QUESTION 16:

Is the following OK? 

Object obj;
String str = "Yertle" ;

obj = str;
((YouthBirthday)obj).greeting();

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