For the questions below, consider the following class definition:
public class AClass
{
protected int x;
protected int y;
public AClass(int a, int b)
{
x = a;
y = b;
}
public int addEm( )
{
return x + y;
}
public void changeEm( )
{
x++;
y--;
}
public String toString( )
{
return "" + x + " " + y;
}
}
-Consider that you want to extend AClass to BClass. BClass will have a third int instance data, z. Which of the following would best define BClass'constructor?
A) public BClass(int a, int b, int c) {
Super(a, b, c);
}
B) public BClass(int a, int b, int c) {
X = a;
Y = b;
Z = c;
}
C) public BClass(int a, int b, int c) {
Z = c;
}
D) public BClass(int a, int b, int c) {
Super(a, b);
Z = c;
}
E) public BClass(int a, int b, int c) {
Super( );
}

Question

Quizplus · Accepted Answer

D) Inheritance is useful because it allows you to reuse code. For this problem, you would want to reuse as much of AClass as possible. Answer D allows you to use AClass'constructor, which expects two int parameters. This sets x and y to be a and b respectively. But since AClass does not have an instance data z, you need to directly assign z to be c in the constructor. The answer in B will also work, but does not reuse any code and so is not as desirable as D. The answers in A and E are syntactically invalid since they do not pass the correct number of parameters to AClass'constructor. Finally, the answer in C only sets z correctly and leaves x and y uninitialized.

For the Questions Below, Consider the Following Class Definition