Kotlin is a modern, concise, and powerful programming language that runs on the JVM (Java Virtual Machine). Since Kotlin compiles down to Java bytecode, understanding the generated bytecode can help developers optimize performance, debug issues, and learn more about how Kotlin works under the hood.

In this article, we’ll explore multiple ways to check Kotlin bytecode in Android Studio. We’ll also learn how to decompile Kotlin bytecode into Java and inspect the compiled .class files.

Why Should You Check Kotlin Bytecode?

Before we dive into the how-to, let’s quickly understand why checking Kotlin bytecode is important:

• Performance Optimization — Analyzing bytecode helps identify unnecessary allocations, redundant operations, or expensive method calls.
• Understanding Kotlin Features — Features like inline functions, lambda expressions, coroutines, and extension functions have unique bytecode representations.
• Debugging Issues — Sometimes, behavior differs between Kotlin and Java. Examining bytecode can help debug potential pitfalls.
• Learning JVM Internals — Developers who want to deepen their knowledge of the JVM can benefit from exploring compiled bytecode.

Method 1 (Recommended): Using “Show Kotlin Bytecode” Tool in Android Studio

Android Studio provides a built-in tool to inspect Kotlin bytecode and decompile it into Java code. Here’s how to use it:

Step 1: Open Your Kotlin File

Open any Kotlin file (.kt) inside your Android Studio project.

Step 2: Open the Kotlin Bytecode Viewer

Option 1: Using Menu Navigation

• Click on Tools in the top menu bar.
• Navigate to Kotlin → Show Kotlin Bytecode.

Option 2: Using Shortcut Command

• Press Ctrl + Shift + A (Windows/Linux) or Cmd + Shift + A (Mac).
• Type “Show Kotlin Bytecode” in the search box and select it.

Step 3: Inspect the Bytecode

Once the Kotlin Bytecode window opens, you’ll see a textual representation of the compiled bytecode.

Step 4: Decompile Bytecode to Java (Optional)

• Click the Decompile button inside the Kotlin Bytecode window.
• This will convert the bytecode into Java-equivalent code, which helps understand how Kotlin translates to Java.

Method 2: Inspecting .class Files in Build Directory

Another way to check Kotlin bytecode is by inspecting the compiled .class files inside your project’s build directory. Here’s how:

Step 1: Enable Kotlin Compiler Options

Modify gradle.properties to ensure the compiler executes in-process:

kotlin.compiler.execution.strategy=in-process

It’s important to note that Android Studio generates .class files regardless. However, when kotlin.compiler.execution.strategy=in-process is specified, the compiler runs within the same process as the Gradle build.

Step 2: Compile the Project

• Build your project by clicking Build → Make Project or using the shortcut Ctrl + F9 (Windows/Linux) or Cmd + F9 (Mac).

Step 3: Locate the Compiled .class Files

• Navigate to the build folder inside your module:
• app/build/.../classes/
• Inside this directory, you’ll find .class files corresponding to your Kotlin classes.

Step 4: Use javap to Inspect Bytecode

To view the actual bytecode, use the javap tool:

javap -c -p MyClass.class

This will print the bytecode instructions for the compiled class.

Additional Tips for Analyzing Kotlin Bytecode

1. Use IntelliJ IDEA for Better Analysis — Since Android Studio is based on IntelliJ IDEA, you can use the same tools for deeper bytecode analysis.
2. Understand the Impact of Kotlin Features — Features like data classes, inline functions, and coroutines generate different bytecode patterns. Observing them can help optimize performance.
3. Experiment with Compiler Flags — The Kotlin compiler provides various options (-Xjvm-default=all, -Xinline-classes, etc.) that affect bytecode generation.

Conclusion

Checking Kotlin bytecode in Android Studio is a valuable skill for developers who want to optimize performance, debug issues, and deepen their understanding of how Kotlin interacts with the JVM. By using the built-in Kotlin Bytecode Viewer, decompiling to Java, and inspecting .class files, you can gain insights into Kotlin’s compilation process.