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Java Interfaces
Question 1
Which of the following statements about Java interfaces is true?
- A
An interface can have instance variables
- B
An interface can extend multiple interfaces
- C
An interface can implement another interface
- D
An interface can have a constructor
Question 2
What is the correct way to declare an interface in Java?
- A
interface MyInterface { void myMethod() {}; }
- B
abstract interface MyInterface { void myMethod(); }
- C
public interface MyInterface { void myMethod(); }
- D
class MyInterface { void myMethod(); }
Question 3
What will be the output of the following code?
interface X {
int VALUE = 10;
}
class Y implements X {
public static void main(String[] args) {
System.out.println(VALUE);
}
}
- A
10
- B
Compilation Error
- C
Runtime Error
- D
NullPointerException
Question 4
Can an interface method be private?
- A
Yes, but only in Java 9 and later
- B
No, interface methods must always be public
- C
Yes, in any Java version
- D
Only if the method is static
Question 5
What is the main difference between class and interface?
- A
Class can’t have variables
- B
Interface can be instantiated
- C
Interface can’t have method bodies (pre Java 8)
- D
Class has only abstract methods
Question 6
Which Java feature allows multiple inheritance of type?
- A
Interface
- B
Abstract class
- C
Inheritance
- D
Static block
Question 7
Can an interface have a method body?
- A
No, never
- B
No, only abstract methods
- C
Yes, using default and static methods (Java 8+)
- D
yes, but only private methods
Question 8
How many abstract methods can a functional interface have?
- A
0
- B
1
- C
2
- D
Unlimited
Question 9
Which of the following is a valid functional interface in Java?
- A
Comparator
- B
Runnable
- C
Callable
- D
All of the above
There are 9 questions to complete.
