Question 1

A subclass inherits _____________ from its superclass.
a. private method
b. protected method
c. public method
d. a and c
e. b and c

Accepted Answer

b and c

Question 2

What exception type does the following program throw? public class Test {
Public static void main(String[] args) {
Object o = new Object();
String d = (String)o;
}
}
A) ArithmeticException
B) No exception
C) StringIndexOutOfBoundsException
D) ArrayIndexOutOfBoundsException
E) ClassCastException

Accepted Answer

The program is trying to cast an object of type Object to type String, which is not allowed. This results in a ClassCastException being thrown at runtime.

Question 3

What exception type does the following program throw? public class Test {
Public static void main(String[] args) {
Object o = null;
System.out.println(o.toString());
}
}
A) ArrayIndexOutOfBoundsException
B) ClassCastException
C) NullPointerException
D) ArithmeticException
E) StringIndexOutOfBoundsException

Accepted Answer

In the given code, a null object is being used to access a method 'toString()', which is not possible and results in a NullPointerException.

Question 4

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(String s) {
System.out.println(s);
}
}
Public class C {
Public static void main(String[] args) {
B b = new B("The constructor of B is invoked");
}
}
A) none
B) "The constructor of B is invoked"
C) "The default constructor of A is invoked" "The constructor of B is invoked"
D) "The default constructor of A is invoked"

Accepted Answer

When an object of class B is created, the constructor of B is invoked which prints "The constructor of B is invoked". However, since class B extends class A, the constructor of A is also invoked before the constructor of B. Therefore, the output will be "The default constructor of A is invoked" followed by "The constructor of B is invoked".

Question 5

What is wrong in the following code?
Test {
main(String[] args) {
Number x = Integer(3);
System.out.println(x.intValue());
System.out.println((Integer)x.compareTo(new Integer(4)));
}
}

Accepted Answer

The answer of What is wrong in the following code?
Test...

Question 6

Which of the following possible modifications will fix the errors in this code? public class Test {
Private double code;
Public double getCode() {
Return code;
}
Protected abstract void setCode(double code);
}
A) Remove abstract in the setCode method declaration.
B) Change protected to public.
C) Add abstract in the class declaration.
D) b and c

Accepted Answer

The class contains an abstract method (setCode), which means the class itself must be declared abstract. Removing abstract from the method or changing its access modifier does not address the fundamental issue that an abstract method exists within a non-abstract class.

Question 7

Write a method to find the max in an array of comparable objects (Assume that the objects in the argument are instances of Comparable). The method signature is as follows:
public static Comparable max(Comparable[] a)

Accepted Answer

The answer of Write a method to find the max...

Question 8

What is the output of running the class C. public class C {
Public static void main(String[] args) {
Object[] o = {new A(), new B()};
System.out.print(o[0]);
System.out.print(o[1]);
}
}
Class A extends B {
Public String toString() {
Return "A";
}
}
Class B {
Public String toString() {
Return "B";
}
}
A) AB
B) BA
C) AA
D) BB
E) None of above

Accepted Answer

When the code runs, it creates an object array `o` with two elements, one of type `A` and one of type `B`. Then it prints out the first (`o[0]`) and second (`o[1]`) elements of the array using `System.out.print()`. 
The `toString()` method is called on each object when it is printed. `A` overrides `toString()` to return the `String` "A", and `B` overrides it to return the `String` "B". Therefore, the output will be "AB".

Question 9

What is wrong in the following code?
Test {
main(String[] args) {
Number x = Integer(3);
System.out.println(x.intValue());
System.out.println));
}
}

Accepted Answer

The answer of What is wrong in the following code?
Test...

Question 10

Analyze the following code. class Test {
Public static void main(String[] args) {
Object x = new Integer(2);
System.out.println(x.toString());
}
}
A) The program has syntax errors because an Integer object is assigned to x.
B) When x.toString() is invoked, the toString() method in the Object class is used.
C) When x.toString() is invoked, the toString() method in the Integer class is used.
D) None of the above.

Accepted Answer

The code declares an Object variable x and assigns it an Integer object with value 2. When x.toString() is invoked, the toString() method in the Integer class is used because x refers to an Integer object. Therefore, the output will be "2". The code is free of syntax errors.

Question 11

The program has a syntax error because the member access operator The java.util.Date class implements java.lang.Cloneable and overrides the equals method to return true if two objects have the same date and time. Show the output of the following code.
import java.util.*;
public class Test extends Object {
public static void main(String[] args) {
Date d1 = new Date();
Date d2 = new Date(349324);
Date d3 = d1;
System.out.println("(1) " + (d1 == d2));
System.out.println("(2) " + (d1 == d3));
System.out.println("(3) " + d1.equals(d2));
System.out.println("(4) " + d1.equals(d3));
}
}

Accepted Answer

The answer of The program has a syntax error because...

Question 12

When you implement a method that is defined in a superclass, you __________ the original method.
A) overload
B) override
C) copy
D) call

Accepted Answer

When you implement a method that is defined in a superclass, you override the original method. Overriding means providing a new implementation for a method in a subclass. The overridden method has the same name, parameters, and return type as the original method in the superclass, but it provides a different implementation.

Question 13

Show the output of running the class Test in the following code: interface A {
Void print();
}
Class C {}
Class B extends C implements A {
Public void print() { }
}
Public class Test {
Public static void main(String[] args) {
B b = new B();
If (b instanceof A)
System.out.println("b is an instance of A");
If (b instanceof C)
System.out.println("b is an instance of C");
}
}
A) Nothing.
B) b is an instance of A.
C) b is an instance of C.
D) b is an instance of A followed by b is an instance of C.

Accepted Answer

Class B extends C and implements A, so an instance of B is considered an instance of both A and C.

Question 14

Write a class named Hexagon that extends GeometricObject and implements the Comparable interface. Assume all six sides of the hexagon are of equal size. The Hexagon class is defined as follows:
public class Hexagon extends GeometricObject implements Comparable {
private double side;
/** Construct a Hexagon with the specified side */
public Hexagon(double side) {
// Implement it
}
/** Implement the abstract method getArea in
GeometricObject */
public double getArea() {
// Implement it (  )
}
/** Implement the abstract method getPerimeter in
GeometricObject */
public double getPerimeter() {
// Implement it
}
/** Implement the compareTo method in
the Comparable interface to */
public int compareTo(Object obj) {
// Implement it (compare two Hexagons based on their areas)
}
}

Accepted Answer

The answer of Write a class named Hexagon that extends...

Question 15

The method _____ overrides the following method: protected double xMethod(int x) {…};
A) private double xMethod(int x) {…}
B) protected int xMethod(double x) {…}
C) public double xMethod(double x) {…}
D) public double xMethod(int x) {…}

Accepted Answer

Overriding a method in Java requires the child method to have the same signature as the parent method, including the return type and parameter types. The only difference allowed is a change in the access level modifier, where the overriding method can have a less restrictive access level. Option D, "public double xMethod(int x) {…}", matches the parent method's signature with an int parameter and a double return type, and uses a less restrictive access level (public instead of protected), making it a correct override.

Question 16

Analyze the following code: public class Test1 {
Public Object max(Object o1, Object o2) {
If ((Comparable)o1.compareTo(o2) >= 0) {
Return o1;
}
Else {
Return o2;
}
}
}
A) The program has a syntax error because Test1 does not have a main method.
B) The program has a syntax error because o1 is an Object instance and it does not have the compareTo method.
C) The program has a syntax error because you cannot cast an Object instance o1 into Comparable.
D) The program would compile if ((Comparable)o1.compareTo(o2) >= 0) is replaced by (((Comparable)o1).compareTo(o2) >= 0).
E) b and d are both correct.

Accepted Answer

Option B is correct because Object class does not have the method compareTo(), so it will give a compilation error.
Option C is incorrect because casting to Comparable is allowed in Java, so there is no syntax error.
Option D is correct because when trying to cast o1 into Comparable, the compiler doesn't know if the method is present in Object or in a subclass of Object. Therefore, we must apply a cast to the object before invoking the method. Hence, ((Comparable) o1).compareTo(o2) is the correct syntax.
Option A is incorrect because not having the main method is not a syntax error. It's only necessary if we want to execute the program as a stand-alone Java application. So, it's not a compilation error but might be a runtime error if we try to run the program directly.

Quiz 2: Elementary Programming

A subclass inherits _____________ from its superclass. a. private method b. protected method c. public method d. a and c e. b and c

What exception type does the following program throw? public class Test { Public static void main(String[] args) { Object o = new Object() ; String d = (String) o; } }

What exception type does the following program throw? public class Test { Public static void main(String[] args) { Object o = null; System.out.println(o.toString() ) ; } }

What is wrong in the following code? Test { main(String[] args) { Number x = Integer(3); System.out.println(x.intValue()); System.out.println((Integer)x.compareTo(new Integer(4))); } }

Which of the following possible modifications will fix the errors in this code? public class Test { Private double code; Public double getCode() { Return code; } Protected abstract void setCode(double code) ; }

Write a method to find the max in an array of comparable objects (Assume that the objects in the argument are instances of Comparable). The method signature is as follows: public static Comparable max(Comparable[] a)

What is wrong in the following code? Test { main(String[] args) { Number x = Integer(3); System.out.println(x.intValue()); System.out.println)); } }

Analyze the following code. class Test { Public static void main(String[] args) { Object x = new Integer(2) ; System.out.println(x.toString() ) ; } }

When you implement a method that is defined in a superclass, you __________ the original method.

The method _____ overrides the following method: protected double xMethod(int x) {…};

Analyze the following code: public class Test1 { Public Object max(Object o1, Object o2) { If ((Comparable) o1.compareTo(o2) >= 0) { Return o1; } Else { Return o2; } } }