Java Programming MCQ Questions - Interfaces
11. Which of these keywords is used by a class to use an interface defined previously?
A. Import
B. import
C. implements
D. Implements
View Answer
Ans : C
Explanation: interface is inherited by a class using implements.
12. 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
View Answer
Ans : A
Explanation: Classes always implements an interface. An interface can extends another interface or multiple interfaces. Hence, answer would be A.
13. 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
View Answer
Ans : A
Explanation: In java, an interface contains only abstract method that can be public and it does not have any method implementation.
14. 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
View Answer
Ans : B
Explanation: No Explanation.
15. 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
View Answer
Ans : D
Explanation: All methods and variables are implicitly public if interface is declared public.
16. What type of methods an interface contain by default?
A. abstract
B. static
C. final
D. private
View Answer
Ans : A
Explanation: By default, interface contains abstract methods. The abstract methods need to be implemented by concrete classes.
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
View Answer
Ans : C
Explanation: The methods of interfaces are always abstract. They provide only method definition.
Output:
$ javac interfaces.java
$ java interfaces
4
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
View Answer
Ans : A
Explanation: Constructor is not provided by interface as objects cannot be instantiated.
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
View Answer
Ans : D
Explanation: The JVM needs to distinctly know which value of variable it needs to use. To avoid confusion to the JVM interfaceName.variableName is mandatory.
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
View Answer
Ans : B
Explanation: No, Constructor, Static Initialization Block, Instance Initialization Block and variables cannot be abstract.
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