Java SE 8 Interview Questions and Answers (Part-2)

In my previous post, I have discussed some important Java SE 8 Interview Questions and Answers. In this post, we are going to discuss some more Java SE 8 Interview Questions and Answers. Before reading this post, please go through my previous post at: “Java SE 8 Interview Questions (Part 1)”.

Java SE 8 Interview Questions

1. What is Internal Iteration in Java SE 8?
2. Differences between External Iteration and Internal Iteration?
3. What are the major drawbacks of External Iteration?
4. What are the major advantages of Internal Iteration over External Iteration?
5. What is the major drawback of Internal Iteration over External Iteration?
6. What is the major advantage of External Iteration over Internal Iteration?
7. When do we need to use Internal Iteration? When do we need to use External Iteration?
8. Differences between Intermediate Operations and Terminal Operations of Java 8’s Stream API?
9. Is it possible to provide method implementations in Java Interfaces? If possible, how do we provide them?
10. What is a Default Method? Why do we need Default methods in Java 8 Interfaces?
11. What is a Static Method? Why do we need Static methods in Java 8 Interfaces?
12. Differences between Functional Programming and Object-Oriented Programming?
13. Explain issues of Old Java Date API? What are the advantages of Java 8’s Date and Time API over Old Date API and Joda Time API?
14. Why do we need new Date and Time API in Java SE 8?Explain how Java SE 8 Data and Time API solves issues of Old Java Date API?
15. What are the Differences between Java’s OLD Java Date API and Java 8’s Date and Time API?
16. What is Multiple Inheritance? How Java 8 supports Multiple Inheritance?
17. What is Diamond Problem in interfaces due to default methods? How Java 8 Solves this problem?

Java SE 8 Interview Questions and Answers

What is Internal Iteration in Java SE 8?

Before Java 8, We don’t Internal Iteration concept. Java 8 has introduced a new feature known as “Internal Iteration”. Before Java 8, Java Language has only External Iteration to iterate elements of an Aggregated Object like Collections, Arrays etc. Internal Iteration means “Iterating an Aggregated Object elements one by one internally by Java API”. Instead of Java Application do iteration externally, We ask Java API to do this job internally.

Differences between External Iteration and Internal Iteration?

What are the major drawbacks of External Iteration?

External Iteration has the following drawbacks:

• We need to write code in Imperative Style.
• There is no clear separation of Responsibilities. Tightly-Coupling between “What is to be done” and “How it is to be done” code.
• Less Readable Code.
• More Verbose and Boilerplate code.
• We have to iterate elements in Sequential order only.
• It does not support Concurrency and Parallelism properly.

What are the major advantages of Internal Iteration over External Iteration?

Compare to External Iteration, Internal Iteration has the following advantages:

• As it follows Functional Programming style, we can write Declarative Code.
• More Readable and concise code.
• Avoids writing Verbose and Boilerplate code
• No need to iterate elements in Sequential order.
• It supports Concurrency and Parallelism properly.
• We can write Parallel code to improve application performance.
• Clear separation of Responsibilities. Loosely-Coupling between “What is to be done” and “How it is to be done” code.
• We need to write code only about “What is to be done” and Java API takes care about “How it is to be done” code.

What is the major drawback of Internal Iteration over External Iteration?

Compare to External Iteration, Internal Iteration has one major drawback:

• In Internal Iteration, as Java API takes care about Iterating elements internally, we do NOT have control over Iteration.

What is the major advantage of External Iteration over Internal Iteration?

Compare to Internal Iteration, External Iteration has one major advantage:

• In External Iteration, as Java API does NOT take care about Iterating elements, we have much control over Iteration.

When do we need to use Internal Iteration? When do we need to use External Iteration?

We need to understand the situations to use either Internal Iteration or External Iteration.

• When we need more control over Iteration, we can use External Iteration.
• When we do NOT need more control over Iteration, we can use Internal Iteration.
• When we need to develop Highly Concurrency and Parallel applications and we , we should use Internal Iteration.

Differences between Intermediate Operations and Terminal Operations of Java 8’s Stream API?

Is it possible to provide method implementations in Java Interfaces? If possible, how do we provide them?

In Java 7 or earlier, It is not possible to provide method implementations in Interfaces. Java 8 on-wards, it is possible. In Java SE 8, We can provide method implementations in Interfaces by using the following two new concepts:

• Default Methods
• Static Methods

What is a Default Method? Why do we need Default methods in Java 8 Interfaces?

A Default Method is a method which is implemented in an interface with “default” keyword. It’s new featured introduced in Java SE 8. We need Default Methods because of the following reasons:

• It allow us to provide method’s implementation in Interfaces.
• To add new Functionality to Interface without breaking the Classes which implement that Interface.
• To provide elegant Backwards Compatibility Feature.
• To ease of extend the existing Functionality.
• To ease of Maintain the existing Functionality.

What is a Static Method? Why do we need Static methods in Java 8 Interfaces?

A Static Method is an Utility method or Helper method, which is associated to a class (or interface). It is not associated to any object. We need Static Methods because of the following reasons:

• We can keep Helper or Utility methods specific to an interface in the same interface rather than in a separate Utility class.
• We do not need separate Utility Classes like Collections, Arrays etc to keep Utility methods.
• Clear separation of Responsibilities. That is we do not need one Utility class to keep all Utility methods of Collection API like Collections etc.
• Easy to extend the API.
• Easy to Maintain the API.

Differences between Functional Programming and Object-Oriented Programming?

NOTE:- For more information about FP, IP and OOP comparisons, Please go through my previous post at: “Compare FP, OOP(IP)”

Explain issues of Old Java Date API? What are the advantages of Java 8’s Date and Time API over Old Date API and Joda Time API?

Java’s OLD Java Date API means Date API available before Java SE 8 that is Date, Calendar, SimpleDateFormat etc. Java’s Old Date API has the following Issues or Drawbacks compare to Java 8’s Date and Time API and Joda Time API.

• Most of the API is deprecated.
• Less Readability.
• java.util.Date is Mutable and not Thread-Safe.
• java.text.SimpleDateFormat is not Thread-Safe.
• Less Performance.

Java SE 8’s Date and Time API has the following Advantages compare to Java’s OLD Date API.

• Very simple to use.
• Human Readable Syntax that is More Readability.
• All API is Thread-Safe.
• Better Performance.

Why do we need new Date and Time API in Java SE 8?Explain how Java SE 8 Data and Time API solves issues of Old Java Date API?

We need Java 8’s Date and Time API to develop Highly Performance, Thread-Safe and Highly Scalable Java Applications. Java 8’s Date and Time API solves all Java’s Old Date API issues by following Immutability and Thread-Safety principles.

What are the Differences between Java’s OLD Java Date API and Java 8’s Date and Time API?

Differences between Java’s OLD Java Date API and Java 8’s Date and Time API:

What is Multiple Inheritance? How Java 8 supports Multiple Inheritance?

Multiple Inheritance means a class can inherit or extend characteristics and features from more than one parent class. In Java 7 or Earlier, Multiple Inheritance is not possible because Java follows “A class should extend one and only one class or abstract class” Rule. However, it’s possible to provide Multiple Implementation Inheritance using Interface because Java follows “A class can extend any number of Interfaces” Rule. However, Java 8 supports “Implementing Methods in Interfaces” by introducing new features: Default methods in Interface. Because of this feature, Java 8 supports Multiple Inheritance with some limitations.

What is Diamond Problem in interfaces due to default methods? How Java 8 Solves this problem?

Java 8 default methods can introduce a diamond problem when a class implements multiple interfaces. It occurs when a Class extends more than one interfaces with the same method implementations (Default method). Sample Java SE 8 Code to show the Diamond Problem with interface default methods.

interface A {
	default void display() {
		System.out.println("A");
	}
}

interface B extends A {
	default void display() {
		System.out.println("B");
	}
}

interface C extends A {
	default void display() {
		System.out.println("C");
	}
}

class D implements B, C {
}

In the above code snippet, class D gives compile-time error as “Duplicate default methods named display with the parameters () and () are inherited from the types C and B”. It’s because Java Compiler will get confused about which display() to use in class D. Class D inherits display() method from both interfaces B and C. To solve this problem, Java 8 has given the following solution.

class D implements B, C {

	@Override
	public void display() {
		B.super.display();
	}
	
}

This B.super.display(); will solve this Diamond Problem. If you want to use C interface default method, then use C.super.display();. That’s all about Java 8 Interview Questions. We will discuss some more Java SE 8 Interview Questions in my coming posts. Please drop me a comment if you like my post or have any issues/suggestions.