Capgemini Java & Spring Boot Interview Questions for 3 years of experience

If you're preparing for a Java & Spring Boot interview at Capgemini. Below are the key Java and Spring Boot interview questions that were asked on March 7th, along with detailed answers.

1. Features of Java 8

Java 8 introduced several new features, including:

• Lambda Expressions – Allows functional programming.
• Functional Interfaces – Interfaces with only one abstract method.
• Stream API – Provides operations for processing collections.
• Optional Class – Avoids NullPointerException.
• Default & Static Methods in Interfaces – Allows method implementation inside interfaces.
• New Date & Time API – LocalDate, LocalTime, LocalDateTime.

Example of Lambda Expression:

@FunctionalInterface
interface Greeting {
    void sayHello();
}

public class LambdaExample {
    public static void main(String[] args) {
        Greeting greet = () -> System.out.println("Hello, Java 8!");
        greet.sayHello();
    }
}

2. Why is String Immutable in Java?

Reasons why String is immutable:

✅ Security – Used in class loading, networking, etc.

✅ Thread Safety – Multiple threads can safely share a String.

✅ Performance – String pooling optimizes memory usage.

✅ Caching in HashMap – Hashcode remains unchanged.

3. Can We Override a Private Method in Java?

No, private methods cannot be overridden because they are not inherited.

Example:

class Parent {
    private void display() {
        System.out.println("Parent class");
    }
}

class Child extends Parent {
    private void display() {  // Not overriding, just a new method in ChildSystem.out.println("Child class");
    }
}

4. How to Create an Immutable Class?

To make a class immutable:

1. Declare the class as final.
2. Mark fields as private final.
3. Do not provide setters.
4. Use a constructor to set values.

Example:

final class ImmutablePerson {
    private final String name;

    public ImmutablePerson(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

5. Singleton Class in Java

A Singleton ensures only one instance exists.

Example: Thread-Safe Singleton Using synchronized

class Singleton {
    private static Singleton instance;

    private Singleton() {}

    public static synchronized Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

6. Can We Return from a void Method?

Yes, we can use return in a void method but without a value.

Example:

void display() {
    System.out.println("Hello");
    return; // Valid but optional
}

7. Hierarchy of Map in

Map (Interface)
  ├── HashMap
  │   ├── LinkedHashMap
  ├── TreeMap (Sorted)
  ├── Hashtable (Thread-Safe)

8. Overriding equals() Method in Java

When overriding equals(), ensure:

• Check instance type
• Compare field values

Example:

class Person {
    private String name;
    
    public Person(String name) {
        this.name = name;
    }

    @Overridepublic boolean equals(Object obj) {
        if (this == obj) return true;
        if (!(obj instanceof Person)) return false;
        Person p = (Person) obj;
        return name.equals(p.name);
    }
}

9. Java Program to Rearrange an Array (First, Last, Alternate)

Example:

Input: [1, 2, 3, 4, 5]

Output: [5, 1, 4, 2, 3]

Code:

import java.util.Arrays;

public class RearrangeArray {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5};
        int[] result = new int[arr.length];

        int left = 0, right = arr.length - 1, index = 0;

        while (left <= right) {
            if (index % 2 == 0) {
                result[index] = arr[right--];
            } else {
                result[index] = arr[left++];
            }
            index++;
        }

        System.out.println(Arrays.toString(result)); // Output: [5, 1, 4, 2, 3]
    }
}

11. Spring Bean Scopes

Scope Description

singleton Default, one instance per container.

prototypeCreates a new instance per request.

requestNew bean per HTTP request (Web).

sessionNew bean per session (Web).

applicationOne instance per servlet context.

websocketOne instance per WebSocket session.

Example of Prototype Scope:

@Component
@Scope("prototype")
public class PrototypeBean {
    public PrototypeBean() {
        System.out.println("Prototype Bean Created");
    }
}

Conclusion

This blog covered key Java and Spring Boot interview questions asked in the Capgemini interview on March 7th. It included Java 8 features, String immutability, Singleton pattern, Bean scopes, Collection vs. Map, and practical coding questions.

Would you like additional Capgemini-specific questions or system design concepts for your next interview?