Interfaces are a crucial aspect of Java, allowing for abstraction and helping in the design of robust and flexible systems. They enable a form of multiple inheritance in Java and are fundamental in the application of the SOLID principles, especially the Interface Segregation Principle. Ready to assess your knowledge of interfaces in Java? Dive into this quiz!
Each question is followed by the correct answer and an explanation to help reinforce your knowledge.
a) Ability to be instantiated
b) Presence of instance variables
c) Absence of method implementations
d) All of the above
Click to View Answer and Explanation Answer: c) Absence of method implementations.
Explanation: Before Java 8, interfaces primarily contained method declarations without implementations. While d) seems correct, interfaces can have static final variables and with Java 8, they can have method implementations via default methods.
2. Why are interfaces crucial in Java? a) For multi-threading
b) For memory management
c) For multiple inheritance
d) For package management
Click to View Answer and Explanation Answer: c) For multiple inheritance.
Explanation: Interfaces enable Java classes to achieve a form of multiple inheritance by implementing multiple interfaces.
3. What is the default access modifier of a method in an interface in Java? a) private
b) protected
c) public
d) None of the above
Click to View Answer and Explanation Answer: c) public.
Explanation: Interface methods are public by default since the idea is for them to be implemented by other classes.
4. Which of these is not allowed in an interface? a) Instance variables
b) Static methods
c) Default methods
d) Abstract methods
Click to View Answer and Explanation Answer: a) Instance variables.
Explanation: Interfaces can have static final variables (constants) but not instance variables.
5. Why were default methods introduced in Java 8 interfaces? a) To provide multiple inheritance
b) To add utility functions
c) To provide backward compatibility with older interface versions
d) For better performance
Click to View Answer and Explanation Answer: c) To provide backward compatibility with older interface versions.
Explanation: Default methods allow developers to add new methods to interfaces with an implementation without affecting classes that already use this interface.
6. Which keyword is used to implement an interface in a class? a) implements
b) extends
c) interface
d) import
Click to View Answer and Explanation Answer: a)implements
Explanation: In Java, the implements keyword is used by classes to adopt the contract specified by an interface.
7. How many interfaces can a Java class implement? a) One
b) Two
c) Four
d) Any number
Click to View Answer and Explanation Answer: d) Any number
Explanation: A Java class can implement any number of interfaces, which is how Java achieves a form of multiple inheritance.
8. Starting from which Java version can an interface contain method implementations? a) Java 5
b) Java 7
c) Java 8
d) Java 9
Click to View Answer and Explanation Answer: c) Java 8
Explanation: From Java 8 onwards, interfaces can have default and static method implementations.
9. Can an interface extend another interface? a) Yes
b) No
c) Only if it provides default implementations
d) Only before Java 8
Click to View Answer and Explanation Answer: a) Yes
Explanation: Interfaces can extend other interfaces, allowing for a hierarchical structure of abstract method declarations.
10. Can a class extend an interface? a) Yes
b) No
c) Only abstract classes
d) Only final classes
Click to View Answer and Explanation Answer: b) No
Explanation: Classes implement interfaces, they don't extend them. Only interfaces can extend other interfaces.
11. How can we achieve multiple inheritance in Java? a) Extending multiple classes
b) Implementing multiple classes
c) Extending multiple interfaces
d) Implementing multiple interfaces
Click to View Answer and Explanation Answer: d) Implementing multiple interfaces
Explanation: Java doesn’t support multiple inheritance with classes. However, it can be achieved by implementing multiple interfaces in a single class.
12. The "diamond problem" in programming refers to... a) Memory issues in OOP
b) Multiple inheritance ambiguity
c) Lack of abstraction
d) Too many static methods
Click to View Answer and Explanation Answer: b) Multiple inheritance ambiguity.
Explanation: The diamond problem occurs when a class inherits from two classes that have a method with the same name, leading to ambiguity. Java avoids this problem by not supporting multiple inheritance of classes.
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