Quiz 5 (incomplete)

Question 1

You can declare two variables with the same name in ________.

Answer 1

different methods in a class

Question 2

Object-oriented programming allows you to derive new classes from existing classes. This is called ________.

Answer 2

inheritance

Question 3

Which of the following statements are true? (Choose two.)

Answer 3

A subclass is usually extended to contain more functions and more detailed information than its superclass.

“class A extends B” means A is a subclass of B.

Question 4

Suppose you create a class Cylinder to be a subclass of Circle. Analyze the following code:

class Cylinder extends Circle {
    double length;

Cylinder(double radius) {
     Circle(radius);
} }

Answer 4

The program has a compile error because you attempted to invoke the Circle class’s constructor illegally.

Question 5

What is the output of running class C?

class A {
    public A() {
         System.out.println("The default constructor of A is invoked");
    }
}

class B extends A {
    public B() {
         System.out.println("The default constructor of B is invoked");
    }
}

public class C {
    public static void main(String[ ] args) {
         B b = new B();
    }
}

Answer 5

“The default constructor of A is invoked”“The default constructor of B is invoked”

Question 6

Analyze the following code:

public class Test { 
    public static void main(String[ ] args) {
         B b = new B();
         b.m(5);
         System.out.println("i is " + b.i);
    }
}

class A {
    int i;

public void m(int i) { 
     this.i = i; 
} }

class B extends A {
    public void m(String s) {
    }
}

Answer 6

The method m is not overridden in B. B inherits the method m from A and defines an overloaded method m in B.

Question 7

Given the following code, find the compile error. (Choose two.)

public class Test {
    public static void main(String[ ] args) {
         m(new GraduateStudent());
         m(new Student());
         m(new Person());
         m(new Object());
    }

public static void m(Student x) {
     System.out.println(x.toString());
} }

class GraduateStudent extends Student {
}

class Student extends Person {
    public String toString() {
         return "Student";
    }
}

class Person extends Object {
    public String toString() {
         return "Person";
    }
}

Answer 7

m(new Person()) causes an error

m(new Object()) causes an error

Question 8

Analyze the following code: (Choose two.)

public class Test {
    public static void main(String[ ] args) {
         Object a1 = new A();
         Object a2 = new Object();
         System.out.println(a1);
         System.out.println(a2);
    }
}

class A {
    int x;
    public String toString() {
         return "A's x is " + x;
    }
}

Answer 8

When executing System.out.println(a2), the toString() method in the Object class is invoked.

When executing System.out.println(a1), the toString() method in the A class is invoked.