What is the point of an abstract class?

Question

ok lets say there was a subclass that inhereited another subclass...like a class Person, a class Student, and a class GraduateStudent; why would i want to make the class person abstract and have a abstract void display(); in it if i want to override that method in the subclasses lower on the inheritance tree? Wouldn't it do the same thing to just make a normal class Person and just not have a void display...and the other 2 over ride it anyways so i seriously dont see what the point of abstract classes are

Answer 1

ok lets say there was a subclass that inhereited
another subclass...like a class Person, a class
Student, and a class GraduateStudent; why would i
want to make the class person abstract and have a
abstract void display(); Because all Persons are required to be able to display(), but there's no reasonable common default behavior for display() that you can put in the base class.
Abstract methods say, "Everything of this type must be able to do this, but it's up to the individual implementations to figure out *how* to do it."
in it if i want to override
that method in the subclasses lower on the
inheritance tree? Wouldn't it do the same thing to
just make a normal class Person and just not have a
void display..Then you couldn't do this: Person p = getAPersonThatMightBeAStudentOrWhateverWeDoNotKnowWhat();
p.display();or this:
void doPersonStuff(Person p) {
  p.display();
Person s1 = new Student();
Student s2 = new Student();
Person t1 = new Teacher();
Teacher t2 = new Teacher();
doPersonStuff(s1);
doPersonStuff(s2);
doPersonStuff(t1);
doPersonStuf(t2);
.and the other 2 over ride it anyways
so i seriously dont see what the point of abstract
classes areI hope you do now.
Message was edited by:
jverd