Java Programming Multiple Choice Questions - Interfaces

This section focuses on the "Interfaces" in Java programming. These Multiple Choice Questions (MCQ) should be practiced to improve the Java programming skills required for various interviews (campus interviews, walk-in interviews, company interviews), placements and other competitive examinations.

1. Which of these keywords is used to define interfaces in Java?

A. interface
B. Interface
C. intf
D. Intf

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2. A java interface can contain _______.

A. Abstract methods(unimplemented) and implemented methods both
B. public Abstract methods
C. public static Final Variables only
D. public static Final Variables and abstract methods both

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3. Which of these access specifiers can be used for an interface?

A. Public
B. private
C. Protected
D. All of the mentioned

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4. Which of the following is a correct interface?

A. abstract interface A { abstract void print(); { }}
B. abstract interface A { print(); }
C. interface A { void print() { } }
D. interface A { void print(); }

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5. Which of the following classes directly implement Set interface?

A. Vector
B. HashSet
C. HashTable
D. LinkedList

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6. Which of these keywords is used by a class to use an interface defined previously?

A. Import
B. import
C. implements
D. Implements

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7. Which is the correct way to inherit and implement the interface?

A. class Cat implements IAnimal{}
B. class Cat import IAnimal{}
C. class Cat extends IAnimal{}
D. None is correct

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8. which of the following is true about methods in an interface in java?

A. An interface can contain only abstract method.
B. We can define a method in an interface
C. Private and protected access modifiers can also be used to declare methods in interface
D. None of the above

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9. Which of the following is the correct way of implementing an interface salary by class manager?

A. class manager imports salary {}
B. class manager implements salary {}
C. class manager extends salary {}
D. none of the mentioned

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10. Which of the following is an incorrect statement about packages?

A. Interfaces are specified public if they are to be accessed by any code in the program
B. Interfaces specifies what class must do but not how it does
C. All variables in interface are implicitly final and static
D. All variables are static and methods are public if interface is defined pubic

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11. Which of these can be used to fully abstract a class from its implementation?

A. Objects
B. Packages
C. Interfaces
D. None of the Mentioned

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12. What is the output of this program?

interface calculate
{
   void cal(int item);
}
class display implements calculate
{
	int x;
	public void cal(int item)
	{
		x = item * item;
	}
}
class Main
{
   public static void main(String args[])
   {
    display arr = new display();
    arr.x = 0;
    arr.cal(2);
    System.out.print(arr.x);
   }
}

A. 0
B. 2
C. 4
D. None of the mentioned

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13. All methods must be implemented of an interface.

A. TRUE
B. FALSE
C. Can be true or false
D. can not say

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14. What type of variable can be defined in an interface?

A. public static
B. private final
C. public final
D. static final

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15. What does an interface contain?

A. Method definition
B. Method declaration
C. Method declaration and definition
D. Method name

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16. What type of methods an interface contain by default?

A. abstract
B. static
C. final
D. private

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17. What will happen if we provide concrete implementation of method in interface?

A. The concrete class implementing that method need not provide implementation of that method
B. Runtime exception is thrown
C. Compilation failure
D. Method not found exception is thrown

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18. What happens when a constructor is defined for an interface?

A. Compilation failure
B. Runtime Exception
C. The interface compiles successfully
D. The implementing class will throw exception

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19. What happens when we access the same variable defined in two interfaces implemented by the same class?

A. Compilation failure
B. Runtime Exception
C. The JVM is not able to identify the correct variable
D. The interfaceName.variableName needs to be defined

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20. Can "abstract" keyword be used with constructor, Initialization Block, Instance Initialization and Static Initialization Block.

A. TRUE
B. FALSE
C. Can be true or false
D. can not say

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