Interview Experience with IBM for an Experienced Java Developer Role
As an experienced Java developer with three years under my belt, I recently had the opportunity to interview with IBM. This blog post details my experience, the questions asked, and the solutions I provided. This might help you prepare for similar roles and understand what to expect.
Interview Date: 15th June 2024
Role: Experienced Java Developer
Duration: 1 hour
Verbal Questions
Q1: Write a code to find the first non-repeating character in a string.
Here’s the solution I provided:
import java.util.HashMap;
import java.util.Map;
class Solution {
public static void main(String[] args) {
String word = "simplest"; // i
Map<Character, Integer> charCount = new HashMap<>();
for (char c : word.toCharArray()) {
charCount.put(c, charCount.getOrDefault(c, 0) + 1);
}
for (char c : word.toCharArray()) {
if (charCount.get(c) == 1) {
System.out.println(c);
break;
}
}
}
}
Q2: How to implement Serialize and Deserialize in Java? Fix the bug in the following code:
import java.io.Serializable;
import java.util.Map;
import java.util.HashMap;
class House implements Serializable {
private static final long serialVersionUID = 1L; // Added serialVersionUID
public House(int number) {
super();
this.number = number;
this.cities = new HashMap<>(); // Initialize cities map
}
Wall wall;
int number;
Map<String, String> cities;
}
class Wall implements Serializable {
private static final long serialVersionUID = 1L; // Added serialVersionUID
int length;
int breadth;
int color;
}
Q3: Create a custom annotation in Java to have a minimum length of 5.
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface MinLength {
int value() default 5;
}
Q4: Create a custom exception in Java.
public class CustomException extends Exception {
public CustomException(String message) {
super(message);
}
}
Q5: How to autowire an interface object in Java if we have multiple classes implementing the interface?
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;
interface Car {
void speed();
}
@Component("swift")
class Swift implements Car {
// Implement speed
}
@Component("kia")
class KIA implements Car {
// Implement speed
}
@Service
class CarService {
@Autowired@Qualifier("swift")
Car car;
}
Q6: Reverse the ArrayList of elements in Java using Stream.
import java.util.Arrays;
import java.util.List;
import java.util.Collections;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args) {
List<String> listOfStrings = Arrays.asList("Facebook", "Twitter", "YouTube", "WhatsApp", "LinkedIn");
List<String> reversedList = listOfStrings.stream()
.sorted(Collections.reverseOrder())
.collect(Collectors.toList());
System.out.println("Reversed ArrayList: " + reversedList);
}
}
Q7: What is the parent interface of Collections?
Answer: The parent interface of Collections is Iterable.
Q8: Types of Functional Interface.
Answer:
- Predicate
- Consumer
- Supplier
- Function
Q9: What does the mvn clean command do?
Answer: It deletes/cleans the target directory.
Q10: Maven command to run the Spring Boot project?
- Answer:
mvn spring-boot:run
Q11: How to read the value from application.properties file in Java?
Answer:
- Using
@Valueannotation to access the values defined in theapplication.properties. - Using
@AutowiredandEnvironment.
Q12: What is the latest Spring Boot version?
- Answer: As of my last update, the latest version was Spring Boot 2.5.5.
Q13: How to load some properties while the server starts in Java?
- Answer: You can use Spring Boot's
@ConfigurationPropertiesannotation to load properties during server startup.
Q14: How to pass command line arguments in Spring Boot?
- Answer: Use
mvn spring-boot:run -Dspring-boot.run.arguments=--person.name=Test
Q15: What are the features of dependency injection in Spring Boot?
Answer: Loose coupling, easier unit testing, and improved code maintainability.
Q16: Types of Dependency Injection?
Answer: Constructor Injection, Setter Injection, and Interface Injection.
Q17: Difference between HashMap, HashSet, and TreeSet.
Answer:
- HashMap:
- Implements the Map interface.
- Stores key-value pairs.
- Uses a hash table data structure.
- Allows one null key and multiple null values.
- HashSet:
- Implements the Set interface.
- Stores unique elements.
- Uses a hash table internally.
- Allows one null element.
- TreeSet:
- Implements the Set interface.
- Stores unique elements in sorted order.
- Uses a Red-Black tree internally.
- Does not allow null elements.
Q18: How to create a thread in Java?
Answer: You can implement threads by extending the Thread class or by implementing the Runnable interface.
public class MyThread extends Thread {
public void run() {
System.out.println("Thread running");
}
public static void main(String[] args) {
MyThread myThread = new MyThread();
myThread.start();
}
}
public class MyRunnable implements Runnable {
public void run() {
System.out.println("Thread running");
}
public static void main(String[] args) {
Thread thread = new Thread(new MyRunnable());
thread.start();
}
}
Q19: Explain the life cycle of a thread.
Answer:
- New: When a thread is created but has not yet started executing.
- Runnable: After calling the
start()method, but the thread may not be executing. - Running: When the CPU scheduler selects the thread for execution.
- Blocked/Waiting: When a thread is waiting for a resource or another thread.
- Timed Waiting: When a thread waits for a specified time.
- Terminated: When a thread completes its execution or is explicitly terminated.
Q21: Optional Keyword in Java.
Answer: Optional is a container object that may or may not contain a non-null value, aiming to reduce NullPointerExceptions.
Q22: Java 8 code to convert a list of lists into a linear list.
public static void main(String[] args) {
List<List<Integer>> listOfLists = new ArrayList<>();
listOfLists.add(Arrays.asList(1, 2, 3));
listOfLists.add(Arrays.asList(4, 5, 6));
listOfLists.add(Arrays.asList(7, 8, 9));
List<Integer> linearList = listOfLists.stream()
.flatMap(List::stream)
.collect(Collectors.toList());
System.out.println("Linear list: " + linearList);
}
Q23: What is @SpringBootApplication Annotation?
Answer: This annotation marks the main class of a Spring Boot application, encapsulating @Configuration, @EnableAutoConfiguration, and @ComponentScan.
Q24: Different Spring Boot starter dependencies.
Answer:
spring-boot-starterspring-boot-starter-webspring-boot-starter-data-jpaspring-boot-starter-data-mongodbspring-boot-starter-securityspring-boot-starter-testspring-boot-starter-actuatorspring-boot-starter-validationspring-boot-starter-mailspring-boot-starter-cache
Q25: Basic design patterns and examples.
Answer:
- Singleton Pattern:
public class Singleton {
private static Singleton instance;
private Singleton() {}
public static Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
- Factory Method Pattern:
public interface Animal {
void makeSound();
}
public class Dog implements Animal {
public void makeSound() {
System.out.println("Woof");
}
}
public class Cat implements Animal {
public void makeSound() {
System.out.println("Meow");
}
}
public interface AnimalFactory {
Animal createAnimal();
}
public class DogFactory implements AnimalFactory {
public Animal createAnimal() {
return new Dog();
}
}
public class CatFactory implements AnimalFactory {
public Animal createAnimal() {
return new Cat();
}
}
Conclusion
Interviewing with IBM was a rigorous but enriching experience. The technical questions tested both my theoretical knowledge and practical skills in Java. I hope this detailed account helps fellow developers prepare for their interviews. Good luck!
Feel free to ask any questions or share your interview experiences in the comments below!