Java MCQ – Classes and Objects

This collection of Java Multiple Choice Questions and Answers (MCQs): Quizzes & Practice Tests with Answer focuses on “Classes and Objects”.
 

1. What is stored in “obj” in the following line of code?

MyClass obj;

A NULL

B Pointer

C Memory address allocated for the object

D Garbage

2. Which of these keywords is used to create a class?

A class

B struct

C int

D None of the above

3. Which of the following statements is a valid declaration of an object that belongs to “MyClass”?

A MyClass obj = new MyClass();

B MyClass obj = new MyClass;

C obj = new MyClass();

D new MyClass obj;

4. Which of these operators is used to allocate memory for an object?

A malloc

B alloc

C new

D realloc

5. Which of the following statements is incorrect?

A Each class should have a main() method

B The program does not require a main() method

C We can only have one main() method in a program

D main() method must be public

6. What is the output of this program?

class Main
{
        public static void main(String args[])
        {
            int x = 3;
            if (x == 3) 
            { 
                int x = 4;
                System.out.println(x);
            }
        } 
}

A Runtime error

B Compilation error

C 3

D 4

B

Two variables with the same name cannot be created in the same class. This produces a compilation error.
 

 

7. What is the output of this program?

class MyClass
{
     int width;
     int height;
     int length;
} 
    
public class MainClass
{
        public static void main(String args[]) 
        {        
             MyClass obj = new MyClass();
             obj.width = 5;
             obj.height = 2;
             obj.length = 5;
             int y = obj.width * obj.height * obj.length; 
             System.out.print(y);
        } 
}

A 10

B 5

C 50

D 25

$ javac MainClass.java
$ java MainClass
50

8. What is the output of this program?

class MyClass
{
     int width;
     int height;
     int length;
} 

public class MainClass
{
        public static void main(String args[]) 
        {
            MyClass objA = new MyClass();
            MyClass objB = new MyClass();
            objA.height = 1;
            objA.length = 2;
            objA.width = 1;
            objB = objA;
            System.out.println(objB.height);
        } 
}

A Runtime error

B Compilation error

C 1

D 2

$ javac MainClass.java
$ java MainClass
1

9. Which of the following statements is correct?

A Public method is accessible to all other classes in the hierarchy

B Public method is only accessible to subclasses of its parent class

C Public method can only be called by the object of its class

D We can access the public method by calling the object of the public class

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