Class Fundamentals & Declaring objects - Java Questions & Answers

This section of our 1000+ Java MCQs focuses on class fundamentals & object declaration in Java Programming Language.

1. What is the stored in the object obj in following lines of Java code?

   box obj;

a) Memory address of allocated memory of object
b) NULL
c) Any arbitrary pointer
d) Garbage
View Answer

Answer: b
Explanation: Memory is allocated to an object using new operator. box obj; just declares a reference to object, no memory is allocated to it hence it points to NULL.

2. Which of these keywords is used to make a class?
a) class
b) struct
c) int
d) none of the mentioned
View Answer

Answer: a
Explanation: None.

3. Which of the following is a valid declaration of an object of class Box?
a) Box obj = new Box();
b) Box obj = new Box;
c) obj = new Box();
d) new Box obj;
View Answer

Answer: a
Explanation: None.

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4. Which of these operators is used to allocate memory for an object?
a) malloc
b) alloc
c) new
d) give
View Answer

Answer: c
Explanation: Operator new dynamically allocates memory for an object and returns a reference to it. This reference is address in memory of the object allocated by new.

5. Which of these statement is incorrect?
a) Every class must contain a main() method
b) Applets do not require a main() method at all
c) There can be only one main() method in a program
d) main() method must be made public
View Answer

Answer: a
Explanation: Every class does not need to have a main() method, there can be only one main() method which is made public.

6. What will be the output of the following Java program?

```
    class main_class 
```
```
    {
```

        public static void main(String args[])

```
        {
```
```
            int x = 9;
```
```
            if (x == 9) 
```
```
            { 
```
```
                int x = 8;
```
```
                System.out.println(x);
```
```
            }
```
```
        } 
```
```
    }
```

a) 9
b) 8
c) Compilation error
d) Runtime error
View Answer

Answer: c
Explanation: Two variables with the same name can’t be created in a class.
output:

$ javac main_class.java
Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	 Duplicate local variable x

7. Which of the following statements is correct?
a) Public method is accessible to all other classes in the hierarchy
b) Public method is accessible only to subclasses of its parent class
c) Public method can only be called by object of its class
d) Public method can be accessed by calling object of the public class
View Answer

Answer: a
Explanation: None.

8. What will be the output of the following Java program?

```
    class box 
```
```
    {
```
```
        int width;
```
```
        int height;
```
```
        int length;
```
```
    } 
```
```
    class mainclass 
```
```
    {
```

        public static void main(String args[])

```
        {        
```
```
             box obj = new box();
```
```
             obj.width = 10;
```
```
             obj.height = 2;
```
```
             obj.length = 10;
```

             int y = obj.width * obj.height * obj.length;

```
             System.out.print(y);
```
```
        } 
```
```
    }
```

a) 12
b) 200
c) 400
d) 100
View Answer

Answer: b
Explanation: None.
output:

$ javac mainclass.java
$ java mainclass
200

9. What will be the output of the following Java program?

```
    class box 
```
```
    {
```
```
        int width;
```
```
        int height;
```
```
        int length;
```
```
    } 
```
```
    class mainclass 
```
```
    {
```

        public static void main(String args[])

```
        {        
```
```
            box obj1 = new box();
```
```
            box obj2 = new box();
```
```
            obj1.height = 1;
```
```
            obj1.length = 2;
```
```
            obj1.width = 1;
```
```
            obj2 = obj1;
```

            System.out.println(obj2.height);

```
        } 
```
```
    }
```

a) 1
b) 2
c) Runtime error
d) Garbage value
View Answer

Answer: a
Explanation: When we assign an object to another object of same type, all the elements of right side object gets copied to object on left side of equal to, =, operator.
output:

$ javac mainclass.java
$ java mainclass
1

10. What will be the output of the following Java program?

```
   class box 
```
```
   {
```
```
        int width;
```
```
        int height;
```
```
        int length;
```
```
   } 
```
```
    class mainclass 
```
```
    {
```

        public static void main(String args[])

```
        {        
```
```
            box obj = new box();
```
```
            System.out.println(obj);
```
```
        } 
```
```
    }
```

a) 0
b) 1
c) Runtime error
d) classname@hashcode in hexadecimal form
View Answer

Answer: d
Explanation: When we print object internally toString() will be called to return string into this format classname@hashcode in hexadecimal form.
output:

$ javac mainclass.java
$ java mainclass
box@130671e

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