What You Should Know As an Android Developer: Levels, Hard Skills, Interview Questions 

The Android operating system has long been a pillar of the mobile app development industry. As of 2024, Android accounts for more than 70% of the mobile OS market, cementing its position as a leading force in tech.

The widespread adoption of Android can be attributed to several factors, including its open-source nature, the growing number of businesses integrating it into their operations, its compatibility with a myriad of devices, and the relatively lower costs associated with Android (vs iOS) app development.

Consequently, Android development is in high demand, offering a wide range of job opportunities. In this article, we delve into the roles and responsibilities of Android developers at different levels of expertise, outline the essential hard skills required, and discuss common interview questions you might face.

To begin with, it is important to note that it will take approximately one year to progress from Trainee to Junior Android developer. The path from Junior to Middle will take two years, and from Middle to Senior another two to three years. However, these time scales are indicative and may vary depending on the developer and the company.

Junior developer

At the Junior level, you will learn a lot. You will dedicate a significant amount of time to becoming acquainted with the environment and essential features of Android Studio. Your primary responsibility will involve coding, while important project decisions will be made by senior or tech lead colleagues. You will implement decisions made by your more experienced colleagues and seek guidance and feedback from them. Additionally, you will likely handle tasks that are relatively simple and not critical for the product. Typically, minimal communication with the client occurs at the Junior level, as this aspect is managed by more experienced colleagues.

The list of hard skills required of an Android developer is similar at all three levels of expertise. The main difference is the depth of knowledge. As a Junior Android developer, you should have foundational knowledge of both Kotlin and Java, as well as familiarity with the Android SDK. You should understand basic principles of object-oriented programming (OOP) and object-oriented design (OOD), along with basic knowledge of design patterns, networking, and databases. These skills are essential for effectively building and maintaining Android applications.

Questions you might expect when applying for a Junior Android developer role:

• What are the four basic principles of OOP?
• What are DRY and KISS?
• What is the Collection structure in Java?
• What is an abstract class?
• What is the difference between ArrayList and LinkedList?
• What are checked and unchecked exceptions in Java?
• What are Android Components?
• What are the types of intents in Android?
• What are the Data class and Sealed class in Kotlin?
• What is the View Lifecycle?

Middle developer 

As a Middle developer, you will play a more significant role in decision-making, architectural design, and client communication. Your expertise will empower you to determine the most effective approach for specific scenarios. Additionally, you may take part in onboarding and mentoring new team members. 

Building on Junior Android developer skills, a mid-level Android developer should have advanced knowledge of Kotlin and Java, along with a thorough understanding of the Android SDK. At this level, you might use Google Developer Console to monitor app performance and user engagement metrics. You will also need strong skills in object-oriented design (OOD) and should be adept at applying complex design and architectural patterns. Additionally, you should have a solid grasp of networking and database management, enabling you to implement sophisticated functionality and effectively optimize app performance. These enhanced skills equip Middle developers to take on more complex software development projects and contribute significantly to their teams. 

At an interview for a Middle Android developer position, you may be asked: 

• What are Any, Nothing, and Unit in Kotlin? 
• What is null safety in Kotlin? 
• What is DI, and why do you need it? 
• What is garbage collection, and how does it work? 
• What are the differences between Inheritance and Composition? 
• What is SOLID? 
• What are high order functions, and what are some examples? 
• What is multithreading (mutex, semaphore, thread synchronization) in Java? 
• What are the differences between launch and async? 
• What are extension functions in Kotlin? 
• What is “suspend” in a Kotlin coroutine? 
• What is infix in Kotlin? 
• What is doze mode in Android? 
• What are the differences between Git merge vs rebase? 
• What are AIDL and IPC in Android? 
• What is the Bind Service, and what is its lifecycle? 
• What is the Foreground Service in Android? 
• How do you properly handle a change of screen orientation? 
• What is the difference between MVP and MVVM? MVVI? 
• What is fun and reified Inline? 
• How would you implement clean architecture in Android? 
• What is GPU overdraw? 
• What is unit testing, and how do you implement it? 

Senior developer 

As a Senior developer, you might write less code but be more engaged in decision-making and communicating with clients. For instance, a client may request that you consider their business needs when developing a solution. They may send a list of requirements that should be analyzed and described in terms of what can and cannot be implemented in Android. The team will then consider the solution’s architecture and write the code. In addition to programming, Senior developers mentor new colleagues and provide feedback on the code of Junior specialists. 

Senior Android developers should have expert knowledge of Kotlin and Java, coupled with comprehensive mastery of the Android SDK. As a Senior developer, you are expected to excel in object-oriented design (OOD) and have a deep understanding of design and architectural patterns, including their advantages, limitations, and optimal applications. Additionally, your expertise should extend to advanced networking techniques and proficient use of Android’s multiple storage options to ensure robust and efficient application performance. This skill set allows Senior developers to lead development efforts and effectively mentor junior team members. 

The list of questions for Senior Android developers might be as follows: 

• What is JNI, and how can you integrate the native C++ library using Java/Kotlin? 
• Generics, in, out in Kotlin. 
• What is SDLC? 
• What is type erasure in Java? 
• What code do you consider non-testable, and how can it be fixed? 
• What is a Delegate in Kotlin? 
• What is structured concurrency? 
• Does Kotlin have checked exceptions? 
• What are extension functions in Kotlin, and how are they implemented under the hood? 
• What are value classes in Kotlin? 
• What is “inline” and how is it implemented under the hood? 
• What Dispatcher is used if the context does not have any dispatcher or any other Continuation Interceptor? 
• What is “scoped storage” in Android? 

Android development offers a dynamic career path filled with opportunities for growth and innovation. Consider joining our team if you are ready to elevate your career and take on new Android development challenges. Check out the latest vacancies at Intellias and find your place in shaping the future of mobile technology.