MainActivity.kt

package com.example.pack.two

// some imports
import com.example.pack.one.MyClass

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val myClass = MyClass()
      
        myClass.setListener(object: MyClass.Listener {
            override fun foo() {
                
            }
        })
      
        myClass.run()
    }
}