“same JVM signature” implementing kotlin interface containing getter method

Question

interface MyInterface {
    fun getTheString(): String
}

class MyClass(var theString: String) : MyInterface {
    ...
}

normally when I have a variable in the constructor for a class, it creates a getter and setter for that variable. In MyClass, the methods getTheString() and setTheString(String) exist when not implementing MyInterface.

When MyClass implements MyInterface, I get the error:

Accidental override: The following declarations have the same JVM signature (getTheString()Ljava/lang/String;):

public final fun (): String defined in MyClass
public abstract fun getTheString(): String defined in MyClass

I also have the error: Class 'MyClass' is not abstract and does not implement abstract member public abstract fun getTheString(): String defined in MyInterface.

So I have a few questions:

Why are 2 getter methods getting generated with the same JVM signature when implementing the interface versus one getter method getting generated without implementing the interface?
Why is it complaining I haven't implemented a getTheString() method when this method is automatically generated by kotlin?
How can I get the getter generated by the variable to become the implementation of the method in the interface?

@EpicPandaForce that resolves the error on var theString, but does not use the method generated by the variable as the implementation of the method within the interface — backcab
If you simply want a custom implementation of a property defined in the constructor, check my answer. — Louis

Alexey Romanov Alexey Romanov · Accepted Answer · 2019-04-02T07:22:42

If the interface is indeed in Kotlin, and you can change it, it should be

interface MyInterface {
    val theString: String
}

in the first place. Java will still see getTheString(), but it's nicer to both implement and use in Kotlin.

Otherwise a good option is

class MyClass(@set:JvmName("setTheString") var _theString: String) : MyInterface {
    override fun getTheString() = _theString
}

Unfortunately, it still has a duplicate getter, and you can't make only the getter private. Or

class MyClass(private var _theString: String) : MyInterface {
    override fun getTheString() = _theString
    fun setTheString(value: String) { 
        _theString = value
    }
}

Note that if the interface is in Java, getTheString() will be visible to Kotlin as a property.

See issues https://youtrack.jetbrains.com/issue/KT-6653 and https://youtrack.jetbrains.com/issue/KT-19444 on the Kotlin bug tracker.

“same JVM signature” implementing kotlin interface containing getter method

1 Answers