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Java Interfaces

Here are 10 essential multiple-choice questions on Java Interfaces, covering key concepts.

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Question 1

Which of the following statements about Java interfaces is true?

An interface can have instance variables
An interface can extend multiple interfaces
An interface can implement another interface
An interface can have a constructor

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Question 2

What will be the output of the following code?

Java

interface A {     default void show() {         System.out.println("A");     } } interface B {     default void show() {         System.out.println("B");     } } class C implements A, B {     public void show() {         A.super.show();     }     public static void main(String[] args) {         new C().show();     } }

A
B
Compilation Error
Runtime Error

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Question 3

What is the correct way to declare an interface in Java?

interface MyInterface { void myMethod() {}; }
abstract interface MyInterface { void myMethod(); }
public interface MyInterface { void myMethod(); }
class MyInterface { void myMethod(); }

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Question 4

Which of the following is true about interfaces and abstract classes?

An abstract class can implement multiple interfaces
An interface can implement an abstract class
An abstract class cannot have final methods
An interface cannot have a static method

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Question 5

What happens if a class implements two interfaces with the same default method?

Compilation fails
Runtime error occurs
The class must override the method
The method from the first interface is used

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Question 6

Which of the following is NOT a valid use of Java interfaces?

Defining method contracts without implementation
Supporting multiple inheritance
Achieving polymorphism
Extending a class

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Question 7

What will be the output of the following code?

Java

interface X {     int VALUE = 10; } class Y implements X {     public static void main(String[] args) {         System.out.println(VALUE);     } }

10
Compilation Error
Runtime Error
NullPointerException

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Question 8

Can an interface method be private?

Yes, but only in Java 9 and later
No, interface methods must always be public
Yes, in any Java version
Only if the method is static

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Question 9

Which of the following correctly implements an interface with a method?

Java

interface Test { void method() {} } class Demo implements Test {}

Java

interface Test { void method(); } class Demo implements Test { public void method() {} }

Java

interface Test { void method(); } class Demo implements Test { void method() {} }

Java

interface Test { void method(); } class Demo extends Test {}

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Question 10

How does Java differentiate between an interface and an abstract class?

An interface cannot have any method implementations, but an abstract class can.
Abstract classes support constructors, but interfaces do not.
A class can implement multiple interfaces but can extend only one abstract class.
All of the above

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