Kotlin vs. Java: Which Is Best for Developing Android Apps?


For over two decades, Java was the most popular programming language for various devices. Since the beginning of mobile applications, developers have been using Java to build thousands of apps. However, Google announced in May 2019 that Kotlin is the preferred programming language for Android apps in Google Play Store.

Considering Kotlin's popularity, is it now better than Java for developing Android apps? Let's take a look.

What Is Kotlin?

Kotlin is a trending open-source programming language from JetBrains. It’s essentially an integrated development environment (IDE). Furthermore, it’s a statically-typed language for JavaScript and Java Virtual Machine (JVM.)

Kotlin is a mix of functional and object-oriented programming that’s simpler, cleaner, and faster to compile compared to Java. However, as Kotlin can compile code to bytecode and run on JVM, it can work on almost any device and platform.

Big tech houses build their Android apps in Kotlin. Some of the popular apps built using this language are Trello, Twitter, and Netflix.

What Is Java?

Java is one of the oldest object-oriented programming languages that found its way into the most advanced programs, Android apps. The primary reason is the Open Handset Alliance made the user interface (UI) of Android OS using Java programming language.

Almost any server, device, and operating system will support Java. Furthermore, as programmers can compile Java programming code into bytecode, it also works on JVM.

Some Java syntaxes are similar to C++ or C. However, Java can’t provide comprehensive low-level programming facilities. App developers used Java to develop many popular apps like Spotify, Cash App, and Signal.

Okay, so you've got a better understanding of Kotlin and Java. Let's dive deeper into the Kotlin vs. Java debate and look at which is better for Android app development.

1. Extension Functions

You can extend the functionalities of an existing class in Kotlin. You can easily do that by adding a prefix of the class name to the function name.

Java language doesn’t support extension functions. You can extend the functionality of an existing class, but the process is time-consuming. You’ll need to inherit the functions from the parent class into the newly-created class.

2. Code Volume & Speed of Coding

For a similar program, Kotlin’s code volume will be way less than that of Java. Kotlin simplifies the efforts of developers by minimizing code errors. Due to the brevity of the Kotlin language, big app development projects prefer Kotlin over Java.

However, the speed of coding these two languages is almost similar. Kotlin may enable the coder to type fewer codes but coming to a solution for a task requires more time on Kotlin. If you’re a coder who has a command over abstract thinking, then you should consider choosing Kotlin.

Though Java language-based programming needs a lot of codes, finding a solution to a task is easier than Kotlin.

3. Null Safety

Null safety ensures that null-dereference issues won’t surface during runtime. The compiler will automatically spot null references and fix them during code compilation. NullPointerExceptions is an infamous error in Java that developers face as Java doesn’t offer null safety.

Kotlin’s system utilizes a null safety feature. So, you won’t encounter the NullPointerExceptions error message.

4. Program Performance

Kotlin comes with additional features that make the developer’s life easier. Developers prefer Kotlin for multithreading apps as it provides extra functionalities. However, these additions cause a program based on Kotlin to compile slower than those based on Java.

It's worth noting, though, that this difference in compilation time is negligible; both of the programming languages convert to bytecode before running on JVM. Therefore, the two programming languages are similar performance-wise.

5. Coroutine Support

In the Android operating system, a long-running task may block the main thread. This, in turn, causes an app to crash or become unresponsive. To overcome this challenge, developers came up with a concurrency design pattern—such as a coroutine.

Kotlin utilizes coroutines to suspend the execution of a code and resume it later when the situation is favorable. Instead of creating multiple threads, the coroutines of Kotlin allow several tasks to run in one thread. It makes the app code cleaner and concise.

Java doesn’t support coroutines. To handle lengthy operations in an Android app, Java lets you create multiple threads. But this makes the programming codebase bulkier, which could subsequently increase the chance of code errors.

6. Smart Casts

If you’re developing a program in Java, you need to inspect the type of variables manually. Again, you need to cast the type manually according to the operator.

On the other hand, Kotlin comes with an extended feature called smart casts. This feature handled all of the casting checks. Its smart compiler automatically replaces the redundant casts with stable values. It does so by tracking the explicit casts and is-checks for immutable values.

7. Data Classes

In Java-based Android app programming, you need to set up the fields or variables to store data. They also need to create the constructor, the getter and setter functions, toString(), equals(), and hashCode().

However, Kotlin simplifies such tasks through automation. You only need to insert the keyword “data” in the class definition. The compiler is smart enough to automatically create several variables or fields like the getter and setter, the constructor, etc.

8. Wildcards

Kotlin doesn’t come with wildcard types. The wildcard’s alternatives in Kotlin are type projections and declaration-site variance.

Java supports wildcards. Usually, a wildcard code is a question mark (?) representing a type that’s not known. It controls the type-safety in the Java-based code of a program.

9. Operator Overloading

Illustration of mathematical operators

In Kotlin, you can effortlessly use various mathematical operators like addition, subtraction, and division. Therefore, you can easily compare objects or perform an equality check using symbols.

However, the java programming language links mathematical operators to specific Java data types. For example, you can only use the addition operator with string and numeric types for addition. Other Java data types can’t reuse the addition operator.

Java or Kotlin?

From the Google Play Store perspective, Kotlin is the official programming language for Android app development. Most developers would want to use Kotlin for the acceptance of their app by the Play Store.

However, Java remains the general-purpose programming language for Android and other platforms. Finally, the developer’s comfort level and the sponsor’s marketing strategy will decide which programming language suits their Android app development project.


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