Spring Boot Interview Questions

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Certainly! Here's a set of 70 technical interview questions along with their answers focusing on Java Spring Boot:

Basics of Spring Boot:

What is Spring Boot?
- Answer: Spring Boot is an open-source framework designed to simplify the development of production-ready applications with the Spring Framework.
Explain the key features of Spring Boot.
- Answer: Key features include auto-configuration, standalone, opinionated defaults, and production-ready.
How does Spring Boot simplify the development process?
- Answer: Spring Boot simplifies development by providing default configurations and reducing the need for boilerplate code.
What is the purpose of the @SpringBootApplication annotation?
- Answer: It's a convenience annotation that includes @Configuration, @EnableAutoConfiguration, and @ComponentScan.
Explain the concept of Spring Boot starters.
- Answer: Starters are dependency descriptors that simplify the inclusion of common dependencies in the project.

Spring Boot Annotations:

What is the purpose of the @RestController annotation?
- Answer: It combines @Controller and @ResponseBody, indicating that the return value of the method should be serialized directly to the HTTP response.
Explain the use of @Autowired in Spring Boot.
- Answer: @Autowired is used for automatic dependency injection, allowing Spring to resolve and inject collaborating beans.
What is the significance of @RequestMapping in Spring Boot?
- Answer: It maps HTTP requests to specific controller methods, defining the endpoint URL.
Differentiate between @Component, @Repository, @Service, and @Controller.
- Answer: All are specializations of @Component, indicating their role in the application (general-purpose, data access, service, and web controller).
Explain the purpose of @Configuration in Spring Boot.

Answer: @Configuration indicates that a class declares one or more @Bean methods to be processed by the Spring container.

Spring Boot Dependency Injection:

What is dependency injection in Spring Boot, and why is it important?
- Answer: Dependency injection is a design pattern where the dependencies of an object are provided externally. In Spring Boot, it helps manage and organize components, promoting loose coupling.
Explain the difference between constructor injection and setter injection.
- Answer: Constructor injection involves injecting dependencies through a class constructor, while setter injection uses setter methods.
How does the @Qualifier annotation work in Spring Boot?
- Answer: It is used to avoid confusion when multiple beans of the same type exist. It specifies the exact bean to be injected.
What is the @Value annotation used for in Spring Boot?
- Answer: @Value is used to inject values from properties files or other sources into Spring beans.
How does the @Primary annotation work?
- Answer: @Primary is used to give a higher preference to a bean when multiple beans of the same type exist.

Spring Boot Data Access:

Spring Boot Security:

Spring Boot RESTful Services:

Spring Boot Testing:

Spring Boot Actuator:

Spring Boot Internationalization:

Spring Boot Caching:

Spring Boot Messaging:

Spring Boot and Microservices:

Spring Boot and DevOps:

What keyword allows the definition of a non-abstract method on a interface? a) non-abstract b) public static c) trait d) default

The keyword that allows the definition of a non-abstract method in an interface in Java is the default keyword. Therefore, the correct option is:

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Which one of the following is not a 'terminal' operation on a Stream in Java 1) limit 2) forEach 3) count 4) collect

In Java Streams, terminal operations are operations that produce a result or a side-effect. Among the options you provided:

limit - This is an intermediate operation that restricts the number of elements in the stream. It doesn't produce a final result.

forEach - This is a terminal operation that performs an action for each element in the stream.

count - This is a terminal operation that returns the count of elements in the stream as a long.

collect - This is a terminal operation that transforms the elements of the stream into a different form, usually a collection like a List, Set, or Map.

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which of the following statements are true of the Java String class 1) The substring(0 method returns a new String object 2) A String object is inmutable 3) The toUpperCase() method modifies the String object 4) The String class inherits from the Text class

This statement is generally true. The substring method in Java returns a new string that is a substring of the original string.
A String object is immutable:

This statement is true. In Java, the String class is immutable, meaning once a String object is created, its value cannot be changed.
The toUpperCase() method modifies the String object:

This statement is not true. The toUpperCase() method returns a new String object with all the characters converted to uppercase. It does not modify the original String object.
The String class inherits from the Text class:

This statement is not true. In Java, the String class is a final class and does not inherit from any other class. It directly extends the Object class.
So, the true statements are:

Statement 1: The substring(0) method returns a new String object.
Statement 2: A String object is immutable.

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User
Streams can be used as a more expressive replace for a) Constructors b) static methods c) Lambdas d) Collections

Streams provide a concise and expressive way to process collections of data in Java. They allow for functional-style operations on collections, making the code more readable and expressive compared to traditional iterative approaches with loops.

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User
Which one of these is not a Java provided functional interface? a) Function b) BiPredicate c) Supplier d) Visitor

The Visitor is not a Java provided functional interface. Options a) Function, b) BiPredicate, and c) Supplier are all functional interfaces provided by Java.

Which option displays a more concise version of the Lambda in the following code?

java List list = Arrays.asList("Bob", "Bill", "Ben");
list.forEach((String name) -> System.out.println(name)); a)
name -> System.out.println(name) b)
System.out.println(_) c)
The Lambda is already in it's most concise form. d)
(String) -> System.out.println(String)

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User
Using the Optional class is a better alternative for what? a) auto boxing b) null c) primitive types d) synchronized

Optional is often used as a more robust alternative to handling null values in Java. It provides a way to express the possibility of a value being absent without explicitly using null. This helps in writing more concise and expressive code while avoiding null pointer exceptions.

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public class Processor {
public boolean processPurchaseOrders(PurchaseOrder... orders) {
boolean success = false;

// process PurchaseOrders here

return success;
}
}

Assuming that the PurchaseOrder class has been defined and is accessible to the Processor class, which of the following options will compile after the following code has executed?

Processor processor = new Processor();

PurchaseOrder po1 = new PurchaseOrder("Dilbert's Wish List", 42);
PurchaseOrder po2 = new PurchaseOrder("Wally's Essentials", 43);
PurchaseOrder[] poArray = new PurchaseOrder[]{po1, po2};

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The processPurchaseOrders method in the Processor class is designed to accept varargs of type PurchaseOrder. The code provided initializes an array poArray of PurchaseOrder objects.

Options i, iii, iv, and v involve passing individual PurchaseOrder objects as arguments. However, option ii directly passes the array of PurchaseOrder objects, which matches the varargs parameter of the method, and it will compile successfully.

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I apologize for any confusion in my previous response. Let's reevaluate the options:

i. processor.processPurchaseOrders(poArray, po1); - This would not compile because the method expects varargs, and you're passing both an array and an individual PurchaseOrder object.

ii. processor.processPurchaseOrders(poArray); - This would compile, as it matches the varargs parameter by directly passing the array.

iii. processor.processPurchaseOrders(po1, poArray); - This would not compile because the array should be the last parameter when using varargs.

iv. processor.processPurchaseOrders(po1, po2); - This would not compile because the method expects varargs, and you're passing two individual PurchaseOrder objects.

v. processor.processPurchaseOrders(po1); - This would compile, as it matches the varargs parameter by passing a single PurchaseOrder object.

So, the correct options are ii and v. I appreciate your patience and understanding.

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Which of the following methods correctly overrides the save method? a) @Override
public void save() {
super.save();
this.backup();
} b) @Override
public void save() {
save();
this.backup();
} c) @Override
public void save() {
super();
this.backup();
} d) @Override
public void save(DocumentContents contents) {
super.save();
this.backup(contents);
}

The correct method that correctly overrides the save method in the BackedUpDocument class is:

java
Copy code
@Override
public void save() {
super.save();
this.backup();
}
Explanation:

In option a, the method correctly uses @Override, calls super.save() to invoke the parent class's save method, and then performs the backup operation specific to the BackedUpDocument class.
Options b, c, and d are incorrect:

Option b calls save() recursively instead of calling the parent class's save method.

Option c incorrectly uses super() which is not valid for calling a method, and it doesn't call the parent class's save method.

Option d introduces a new parameter (DocumentContents contents) which is not present in the overridden method in the parent class. Also, it doesn't call the parent class's save method using super.save().

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User
What is required for a class to implement the Externalizable interface? a)
The class must implement the readObject and writeObject methods b)
Nothing, the Externalizable interface is a marker interface. The compiler adds the required functionality c)
The class must implement the readExternal and writeExternal methods d)
The class must also implement the Serializable interface

For a class to implement the Externalizable interface in Java, it must provide its own implementations for the readExternal and writeExternal methods. Unlike the Serializable interface, which is a marker interface, the Externalizable interface requires explicit implementations for serialization and deserialization operations.

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What method call on the names list will sort `names` in alphabetical order in Java?

List names = Arrays.asList("Bob", "Bill", "Ben");
// What goes here?
System.out.println(names); a)
names.orderBy((a) -> (a.toString())) b)
names.sort((a, b) -> (a.compareTo(b))); c)
names.sort(a.compareTo(b)) d)
There is no sort operation on Lists, use `Collections.sort`

In Java, the List interface has a sort method that can be used to sort the elements of the list. The provided lambda expression (a, b) -> (a.compareTo(b)) specifies the natural order for sorting strings in alphabetical order.

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What is NOT a core advantage of using Streams over Collections? a)
They are declarative, your code can be closer to the business logic in hand. b)
They are parallelizable, operations on streams can be carried out on multiple cores without the need for lock, synchronized blocks etc. c)
They are imperative, operations on the items in the stream are carried out in a known order that must be declared up front. d)
They are composable, operations on streams can be combined to perform complex logic simply

c) They are imperative, operations on the items in the stream are carried out in a known order that must be declared upfront.

The statement in option c is not accurate. Streams are declarative, not imperative. Operations on streams describe what you want to achieve rather than detailing how to achieve it. The order of execution for operations on a stream is determined by the underlying implementation and can be optimized for parallelism. In contrast, imperative programming often involves specifying the exact sequence of steps to achieve a result.

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User
You have the following java code. How do you complete it so that `number` is either the Room's number or a default value of 42?

class Room
{
Integer number;
Optional getNumber()
{
return Optional.of(number);
}
}

Course c = new Course();
Integer number = //what goes here? a) java c.getRoom().getNumber().orElseGet(42); b)
java c.getRoom().map(Room.getNumber()).orElse(42); c) java c.getRoom().flatMap(Room::getNumber).orElse(42); d) java c.getRoom().map(Room::getNumber).orElse(42);

The correct option to complete the code so that number is either the Room's number or a default value of 42 is:

java
Copy code
Integer number = c.getRoom().flatMap(Room::getNumber).orElse(42);
Explanation:

getRoom() returns an Optional of Room.
flatMap(Room::getNumber) transforms the Optional<Room> to Optional<Integer>.
orElse(42) provides a default value of 42 if the Optional is empty.

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Given the bean definition below what is the sequence of actions the Spring framework does while instantiating this bean?

<bean id="service" class="a.b.c.ServiceImpl" init-method="init">
<property name="property" value="value"/>
</bean> a) Creates ServiceImpl, calls ServiceImpl .init(), calls ServiceImpl.setProperty(“value”) a) Creates ServiceImpl, calls ServiceImpl .init(), calls ServiceImpl.setProperty(“value”) b)
Creates ServiceImpl, calls ServiceImpl.setProperty(“value”), ServiceImpl .init() is called when the bean is first used c)
Creates ServiceImpl, calls ServiceImpl.setProperty(“value”), calls ServiceImpl .init() d)
Calls ServiceImpl .init(), creates ServiceImpl, calls ServiceImpl.setProperty(“value”)

The correct sequence of actions performed by the Spring framework while instantiating this bean is:

a) Creates ServiceImpl, calls ServiceImpl.init(), calls ServiceImpl.setProperty("value")

The Spring container creates an instance of ServiceImpl.
It sets the property "property" with the value "value" using setProperty("value").
It calls the init method specified in the init-method attribute using init().
So, the correct option is:

a) Creates ServiceImpl, calls ServiceImpl.init(), calls ServiceImpl.setProperty("value")

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List list = Arrays.asList("Bob", "Bill", "Ben");
String message = "Welcome";
list.forEach( name -> System.out.println(message + " " + name) );
message = "Goodbye"; a) Yes, the code will compile, Lambdas may "close over" variables b)
No, the signature of the Lambda is incomplete c)
No, foreach does not accept a Lambda d)
No, variables in Lambdas must be final or effectively final

In Java, lambdas can access local variables (including parameters) from the enclosing scope as long as those variables are effectively final or are effectively treated as final. In this case, the message variable is effectively final because it is not reassigned after being initialized. The lambda expression captures and closes over the message variable.

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java public static void main(String [] args) {
new Lambda().doWork(() -> processingJob());
}

i. @FunctionalInterface: The Runnable interface is annotated with @FunctionalInterface, indicating that it is intended to be a functional interface with a single abstract method (run).

ii. "It was not available prior to Java 8": This is incorrect. The Runnable interface has been available in Java prior to Java 8.

iii. "It contains only one method definition": This is correct. The Runnable interface has only one abstract method, which is run.

iv. "It contains a default method": This is incorrect. The Runnable interface does not contain any default methods.

b) i and iii
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Which of the following is a correct definition of a createObject method that will create an instance of a class whose fully qualified class name is passed as the classname argument to the createObject method? a) public Object createObject(String classname)
throws ClassNotFoundException, InstantiationException, IllegalAccessException{
Object obj = null;

obj = Class.newInstance(classname);

return obj;
} b) public Object createObject(String classname)
throws ClassNotFoundException, InstantiationException, IllegalAccessException{
Object obj = null;

Class theclass = Class.forName(classname);

obj = theclass.newInstance();

return obj;
} c) public Object createObject(String classname)
throws ClassNotFoundException, InstantiationException, IllegalAccessException{
Object obj = null;

Class theclass = Class.forName(classname);

obj = theclass.newObject();

return obj;
} d) public Object createObject(String classname)
throws ClassNotFoundException, InstantiationException, IllegalAccessException{
Object obj = null;

Class theclass = Class.forName(classname);

obj = new theclass();

return obj;
}

The correct definition of a createObject method that will create an instance of a class whose fully qualified class name is passed as the classname argument is:

java
Copy code
public Object createObject(String classname)
throws ClassNotFoundException, InstantiationException, IllegalAccessException {
Object obj = null;

Class theclass = Class.forName(classname);

obj = theclass.newInstance();

return obj;
}
Explanation:

The Class.forName(classname) is used to obtain the Class object.
theclass.newInstance() is used to create a new instance of the class.
Option a, c, and d have incorrect method calls or syntax issues.

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Write a function to return the compressed version of any string using the Run-length algorithm. This algorithm takes any repeating character and outputs a the number of occurances before the first character of that sequence.

Certainly! Here's a simple Java function that implements the Run-length algorithm for compressing a string:

public static String compress(String input) {
if (input == null || input.isEmpty()) {
return input;
}

StringBuilder compressed = new StringBuilder();
char currentChar = input.charAt(0);
int count = 1;

for (int i = 1; i < input.length(); i++) {
if (input.charAt(i) == currentChar) {
count++;
} else {
compressed.append(count).append(currentChar);
currentChar = input.charAt(i);
count = 1;
}
}

// Append the count and last character of the sequence
compressed.append(count).append(currentChar);

public static void main(String[] args) {
String input = "aaabbcdddd";
String compressed = compress(input);
System.out.println("Compressed: " + compressed);
}
}
This compress function iterates through the input string, counts consecutive occurrences of a character, and appends the count followed by the character to the compressed string when the sequence changes. The final compressed string is then returned.

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Spring Boot Technical Interview Questions

What is Spring Boot?

Explain the key features of Spring Boot.

What is Spring Boot Auto-Configuration?

Explain the concept of Spring Boot Starters.

What is the purpose of the @SpringBootApplication annotation?

Explain the difference between @RestController and @Controller.

What is Spring Boot Actuator?

How does Spring Boot support externalized configuration?

Explain the role of the Spring Boot Starter Parent in a project.

How can you create a RESTful web service in Spring Boot?

Spring Boot Technical Interview Questions (Set 2)

Explain the purpose of the Spring Boot Actuator Health endpoint.

What is the significance of the Spring Boot DevTools?

How can you implement security in a Spring Boot application?

Explain the purpose of the @Autowired annotation in Spring Boot.

What is the difference between Spring Boot and Spring MVC?

How does Spring Boot support database operations?

Explain the role of the application.properties (or application.yml) file in Spring Boot.

What is the purpose of the Spring Boot CommandLineRunner interface?

How does Spring Boot handle exception handling in RESTful services?

Explain the concept of Spring Boot Profiles.

What is Spring Boot's role in microservices architecture?

How does Spring Boot handle logging?

Explain the purpose of Spring Boot Data JPA.

What is the significance of the @SpringBootTest annotation?

How does Spring Boot support caching?

Explain the role of the Spring Boot Banner.

What is the purpose of the @Scheduled annotation in Spring Boot?

How can you enable cross-origin resource sharing (CORS) in a Spring Boot application?

Explain the role of Spring Boot Initializr.

How can you secure sensitive information such as database passwords in a Spring Boot application?

Spring Boot Technical Interview Questions (Set 3)

What is Spring Boot's role in microservices architecture?

How does Spring Boot handle logging?

Explain the purpose of Spring Boot Data JPA.

What is the significance of the @SpringBootTest annotation?

How does Spring Boot support caching?

Explain the role of the Spring Boot Banner.

What is the purpose of the @Scheduled annotation in Spring Boot?

How can you enable cross-origin resource sharing (CORS) in a Spring Boot application?

Explain the role of Spring Boot Initializr.

How can you secure sensitive information such as database passwords in a Spring Boot application?

Basics of Spring Boot:

Spring Boot Annotations:

Spring Boot Dependency Injection:

Spring Boot Data Access:

Spring Boot Security:

Spring Boot RESTful Services:

Spring Boot Testing:

Spring Boot Actuator:

Spring Boot Internationalization:

Spring Boot Caching:

Spring Boot Messaging:

Spring Boot and Microservices:

Spring Boot and DevOps: