My Favorite Kotlin companion object

It can be defined in a class as shown below.

class Base {
    companion object {
        val type: Int = 0
    }
}

It can be accessed like a static variable in Java, using Class.variable.

1. Primitive type or String #

If you want a primitive type or String to be declared as public static final in the decompiled class, you prepend const val to the type. If you only use val, it will be as follows.

When using const val #

kotlin

// 
class Base {
    companion object {
        const val type: Int = 0
    }
}

java

class Base {
    public static final int type = 0;
}

When using val #

kotlin

class Base {
    companion object {
        val type: Int = 0
    }
}

java

class Base {
    private static final int type = 0;

    public static final class Companion {
        public final int getType(){
            return Base.type;
        }
    }
}

Non-primitive type #

For reference types that are not primitive types or Strings, a slightly different approach is needed, as using const will result in an error.

You can use @JvmField to make it decompile as public static final.

When using val #

kotlin

class Base {
    companion object {
        val type: User = User()
    }
}

java

class Base {
    private static final User type = new User();

    public static final class Companion {
        public final User getType(){
            return Base.type;
        }
    }
}

When using @JvmField #

kotlin

class Base {
    companion object {
        @JvmField
        val type: User = User()
    }
}

java

class Base {
    public static final User type = new User();
}