How to convert a kotlin source file to a java source file

Question

I have a Kotlin source file, but I want to translate it to Java.

How can I convert Kotlin to Java source?

Answer 1

As @Vadzim said, in IntelliJ or Android Studio, you just have to do the following to get java code from kotlin:

1. Menu > Tools > Kotlin > Show Kotlin Bytecode
2. Click on the Decompile button
3. Copy the java code

Update:

With a recent version (1.2+) of the Kotlin plugin you also can directly do Menu > Tools > Kotlin -> Decompile Kotlin to Java.

Answer 2

You can compile Kotlin to bytecode, then use a Java disassembler.

The decompiling may be done inside IntelliJ Idea, or using FernFlower https://github.com/fesh0r/fernflower (thanks @Jire)

There was no automated tool as I checked a couple months ago (and no plans for one AFAIK)

Answer 3

you can go to Tools > Kotlin > Show kotlin bytecode

Answer 4

I compile Kotlin to byte code and then de-compile that to Java. I compile with the Kotlin compiler and de-compile with cfr.

My project is here.

This allows me to compile this:

package functionsiiiandiiilambdas.functions.p01tailiiirecursive

tailrec fun findFixPoint(x: Double = 1.0): Double =
        if (x == Math.cos(x)) x else findFixPoint(Math.cos(x))

To this:

package functionsiiiandiiilambdas.functions.p01tailiiirecursive;

public final class ExampleKt {
  public static final double findFixPoint(double x) {
    while (x != Math.cos(x)) {
      x = Math.cos(x);
    }
    return x;
  }

  public static /* bridge */ /* synthetic */ double findFixPoint$default(
      double d, int n, Object object) {
    if ((n & 1) != 0) {
      d = 1.0;
    }
    return ExampleKt.findFixPoint(d);
  }
}

Answer 5

To convert a Kotlin source file to a Java source file you need to (when you in Android Studio):

1. Press Cmd-Shift-A on a Mac, or press Ctrl-Shift-A on a Windows machine.

   

2. Type the action you're looking for: Kotlin Bytecode and choose Show Kotlin Bytecode from menu.

3. Press Decompile button on the top of Kotlin Bytecode panel.

4. Now you get a Decompiled Java file along with Kotlin file in a adjacent tab:

Hope this helps.

Answer 6

As @louis-cad mentioned "Kotlin source -> Java's byte code -> Java source" is the only solution so far.

But I would like to mention the way, which I prefer: using Jadx decompiler for Android.

It allows to see the generates code for closures and, as for me, resulting code is "cleaner" then one from IntelliJ IDEA decompiler.

Normally when I need to see Java source code of any Kotlin class I do:

• Generate apk: ./gradlew assembleDebug
• Open apk using Jadx GUI: jadx-gui ./app/build/outputs/apk/debug/app-debug.apk

In this GUI basic IDE functionality works: class search, click to go declaration. etc.

Also all the source code could be saved and then viewed using other tools like IntelliJ IDEA.

Answer 7

1. open kotlin file in android studio
2. go to tools -> kotlin ->kotlin bytecode
3. in the new window that open beside your kotlin file , click the decompile button . it will create java equivalent of your kotlin file .