Answered: Assume that we have four classes:…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Question

Assume that we have four classes: Person, Teacher, Student, and PhDStudent. Teacher
and Student are both subclasses of Person. PhDStudent is a subclass of Student.
A.Which of the following assignments are legal, and why or why not?
Person p1 = new Student();
Person p2 = new PhDStudent();
PhDStudent phd1 = new Student();
Teacher t1 = new Person();
Student s1 = new PhDStudent();
Suppose that we have the following legal declarations and assignments:
Person p1 = new Person();
Person p2 = new Person();
PhDStudent phd1 = new PhDStudent();
Teacher t1 = new Teacher();
Student s1 = new Student();
B.Based on those just mentioned, which of the following assignments are
legal, and why or why not?
s1 = p1;
s1 = p2;
p1 = s1;
t1 = s1;
s1 = phd1;
phd1 = s1;

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