Why Android Developers Should Learn Java

Android Development · Java 2026

Why Android Developers Should Learn Java

SECTION 01Android is built on Java

The Android SDK itself is written in Java — and even when you use Kotlin, you're still compiling to bytecode and calling Java-based APIs. Understanding Java means understanding what's really happening under the hood.

SECTION 02Legacy codebases need Java

Millions of Android apps are still in Java. When a company hires an Android developer, they often need someone who can read, maintain, and modernise existing Java code.

// Java — a common Android Activity
public class MainActivity extends AppCompatActivity {
    private TextView greeting;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        greeting = findViewById(R.id.greeting);
        greeting.setText("Hello, Android!");

        Button button = findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                greeting.setText("Button clicked!");
            }
        });
    }
}

// Kotlin — the same Activity
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val greeting = findViewById<TextView>(R.id.greeting)
        greeting.text = "Hello, Android!"

        val button = findViewById<Button>(R.id.button)
        button.setOnClickListener {
            greeting.text = "Button clicked!"
        }
    }
}

// Kotlin compiles down to the same bytecode
// Understanding Java helps you understand both.

SECTION 03Interviews still test Java & DSA

Even if the job is Kotlin-first, most Android interviews still test core Java, DSA, and OOP concepts. This is where knowing Java pays off.

• Data structures & algorithms — most DSA content and interview problems are in Java.
• OOP principles — classes, inheritance, interfaces, polymorphism.
• Collections framework — ArrayList, HashMap, etc., still core interview material.
• Concurrency — threads, executors, coroutines vs threads.
• Android-specific Java — Activity lifecycle, Context, Intents.

SECTION 04Career options beyond Android

Java isn't just for Android — it's the backbone of backend systems, enterprise software, and big data. Learning Java opens career paths far beyond mobile development.

SECTION 05How to learn Java as an Android dev

If you're already comfortable in Kotlin, learning Java is easier than you think. Here's a focused roadmap:

• Learn syntax basics — classes, methods, types, control flow.
• Master OOP — inheritance, interfaces, abstract classes, polymorphism.
• Learn the collections framework — List, Set, Map, and their implementations.
• Understand generics — crucial for Android APIs.
• Study concurrency — threads, ExecutorService, and how they compare to Kotlin coroutines.
• Read real Android code — look at open-source Android apps written in Java.
• Build a small project — recreate a simple Kotlin app in Java to see the differences.

SECTION 06Interview Q&A — Java for Android Developers

SECTION 07Test yourself — Java for Android Developers

SECTION 08Frequently asked questions

SECTION 09Related reads