Deutsche Telekom Digital Labs Software Engineer Interview Questions, Process, and Tips

Static is used to define class-level variables and methods, while final is used to define constants that cannot be changed.

• Static variables belong to the class itself, while final variables are constants that cannot be modified.

• Static methods can be called without creating an instance of the class, while final methods cannot be overridden.

• Static variables are shared among all instances of a class, while final variables...read more

ArrayList is better for random access, LinkedList is better for frequent insertions/deletions.

• ArrayList uses dynamic array to store elements, LinkedList uses doubly linked list.

• ArrayList provides fast random access to elements using index, LinkedList provides fast insertion/deletion at any position.

• Example: ArrayList is suitable for scenarios where random access is required like searching, LinkedList is suitable for sc...read more

Java8 introduced several new features including lambda expressions, functional interfaces, streams, and default methods.

• Lambda expressions allow you to write code in a more concise and readable way.

• Functional interfaces are interfaces with a single abstract method, which can be implemented using lambda expressions.

• Streams provide a way to work with collections of objects in a functional style.

• Default methods allow inte...read more

Using streams in Java 8 to filter and map a list of numbers

• Create a list of numbers

• Use stream to filter out even numbers

• Use map to square each number

• Collect the results into a new list

Program to print even and odd numbers from 1 to 20 using 2 threads alternately.

• Create two threads, one for printing even numbers and one for printing odd numbers.

• Use wait(), notify(), and notifyAll() to ensure alternate printing.

• Ensure synchronization between the two threads to avoid race conditions.

• Example: Thread 1 prints even numbers (2, 4, 6, ...) and Thread 2 prints odd numbers (1, 3, 5, ...).

Strings are immutable to ensure data integrity and security.

• Immutable strings prevent accidental changes to data

• Immutable strings allow for safe sharing of data between different parts of a program

• Immutable strings help prevent security vulnerabilities like SQL injection attacks

Default methods in Java 8 allow interfaces to have method implementations, enabling backward compatibility and reducing code duplication.

• Default methods were introduced in Java 8 to provide a way to add new methods to interfaces without breaking existing implementations.

• They allow interfaces to have method implementations, which was not possible before Java 8.

• Default methods can be overridden in implementing classes to...read more

Using Java8 streams to solve a problem

• Use stream() method to convert a collection into a stream

• Use filter() method to filter elements based on a condition

• Use map() method to transform elements

• Use collect() method to collect the elements into a new collection

Checked exceptions are exceptions that must be either caught or declared in the method signature.

• Checked exceptions are subclasses of Exception (excluding RuntimeException and its subclasses)

• Checked exceptions must be either caught using try-catch block or declared in the method signature using 'throws' keyword

• Examples of checked exceptions in Java include IOException, SQLException, and ClassNotFoundException

Annotation used to mark a class as a Spring Boot application

• Combines @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations

• Used to bootstrap and launch a Spring application

• Automatically scans for Spring components in the package and sub-packages

Annotation used in Spring to specify which bean to autowire

• Used to disambiguate when multiple beans of the same type are present

• Can be used with @Autowired to specify which bean to inject

• Helps in resolving dependencies when multiple beans of the same type are available

Microservices are a software development technique where an application is composed of small, independent services that communicate with each other.

• Microservices are designed to be small, focused on specific tasks, and independently deployable.

• Each microservice typically runs its own process and communicates with other services through APIs.

• Microservices allow for easier scalability, flexibility, and maintenance compar...read more

Microservices communicate with each other through APIs, messaging queues, or service meshes.

• APIs: Microservices can communicate with each other by exposing APIs that allow them to send and receive data.

• Messaging queues: Microservices can use messaging queues like RabbitMQ or Kafka to send messages to each other asynchronously.

• Service meshes: Microservices can communicate through a service mesh like Istio, which handles...read more

The project involves creating a web-based platform for online shopping with features like user registration, product browsing, shopping cart, and payment processing.

• User registers on the platform with personal information

• User browses products by category or search

• User adds products to the shopping cart

• User proceeds to checkout and makes payment

• Order is confirmed and user receives a confirmation email

Find the minimum element in an array of strings

• Iterate through the array and compare each element to find the minimum

• Use built-in functions like Math.min() or sort() to find the minimum

• Handle edge cases like empty array or array with only one element

Reverse a linked list by changing the next pointers of each node

• Iterate through the linked list and change the next pointers to reverse the list

• Use three pointers - prev, current, and next to keep track of nodes

• Example: 1 -> 2 -> 3 -> 4 -> null, after reversing: 4 -> 3 -> 2 -> 1 -> null