Questions and answers for exam Preparation

MCQs

Total Questions : 30 | Page 3 of 3 pages

What is the output of this program?

class A {
public int i;
protected int j;
}
class B extends A {
int j;
void display() {
super.j = 3;
System.out.println(i + " " + j);
}
}
class Output {
public static void main(String args[])
{
B obj = new B();
obj.i=1;
obj.j=2;
obj.display();
}
}

Discuss Question

Answer: Option A. -> 1 2

Both class A & B have member with same name that is j, member of class B will be called by

default if no specifier is used. I contains 1 & j contains 2, printing 1 2.
output:
$ javac Output.java
$ java Output
1 2

Question 22.

What is the output of this program?

class A {
public int i;
public int j;
A() {
i = 1;
j = 2;
}
}
class B extends A {
int a;
B() {
super();
}
}
class super_use {
public static void main(String args[])
{
B obj = new B();
System.out.println(obj.i + " " + obj.j)
}
}

1 2
2 1
Runtime Error
Compilation Error

Discuss Question

Answer: Option A. -> 1 2

Keyword super is used to call constructor of class A by constructor of class B. Constructor of

Question 23.

What is the output of this program?

class A {
public int i;
private int j;
}
class B extends A {
void display() {
super.j = super.i + 1;
System.out.println(super.i + " " + super.j);
}
}
class inheritance {
public static void main(String args[])
{
B obj = new B();
obj.i=1;
obj.j=2;
obj.display();
}
}

2 2
3 3
Runtime Error
Compilation Error

Discuss Question

Answer: Option D. -> Compilation Error

class contains a private member variable j, this cannot be inherited by subclass B and does not have access to it.
output:
$ javac inheritance.java
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
The field A.j is not visible

Question 24.

What is the output of this program?

class A {
int i;
}
class B extends A {
int j;
void display() {
super.i = j + 1;
System.out.println(j + " " + i);
}
}
class inheritance {
public static void main(String args[])
{
B obj = new B();
obj.i=1;
obj.j=2;
obj.display();
}
}

Discuss Question

Answer: Option C. -> 2 3

None
output:
$ javac inheritance.java
$ java inheritance
2 3

Question 25.

What is the output of this program?

class A {
int i;
void display() {
System.out.println(i);
}
}
class B extends A {
int j;
void display() {
System.out.println(j);
}
}
class inheritance_demo {
public static void main(String args[])
{
B obj = new B();
obj.i=1;
obj.j=2;
obj.display();
}
}

0
1
2
Compilation Error

Discuss Question

Answer: Option C. -> 2

class A & class B both contain display() method, class B inherits class A, when display() method

is called by object of class B, display() method of class B is executed rather than that of Class A.
output:
$ javac inheritance_demo.java
$ java inheritance_demo
2

Question 26.

Which of the following statements are incorrect?

public members of class can be accessed by any code in the program.
private members of class can only be accessed by other members of the class.
private members of class can be inherited by a sub class, and become protected members in sub class.
protected members of a class can be inherited by a sub class, and become private members of the sub class.

Discuss Question

Answer: Option C. -> private members of class can be inherited by a sub class, and become protected members in sub class.

private members of a class cannot be inherited by a sub class.

Question 27.

Which of these is correct way of inheriting class A by class B?