In Kotlin it would be
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private fun setupToolbar(){
toolbar.title = getString(R.string.YOUR_TITLE)
setSupportActionBar(toolbar)
supportActionBar?.setDisplayHomeAsUpEnabled(true)
supportActionBar?.setDisplayShowHomeEnabled(true)
}
// don't forget click listener for back button
override fun onSupportNavigateUp(): Boolean {
onBackPressed()
return true
}