Kotlin Android start new Activity

Simply you can start an Activity in KOTLIN by using this simple method,

val intent = Intent(this, SecondActivity::class.java)
intent.putExtra("key", value)
startActivity(intent)

To start a new Activity ,

startActivity(Intent(this@CurrentClassName,RequiredClassName::class.java)

So change your code to :

class MainActivity : AppCompatActivity() {

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

    fun buTestUpdateText2 (view: View) {
        startActivity(Intent(this@MainActivity,ClassName::class.java))

        // Also like this 

        val intent = Intent(this@MainActivity,ClassName::class.java)
        startActivity(intent)
    }

To start an Activity in java we wrote Intent(this, Page2.class), basically you have to define Context in first parameter and destination class in second parameter. According to Intent method in source code -

 public Intent(Context packageContext, Class<?> cls)

As you can see we have to pass Class<?> type in second parameter.

By writing Intent(this, Page2) we never specify we are going to pass class, we are trying to pass class type which is not acceptable.

Use ::class.java which is alternative of .class in kotlin. Use below code to start your Activity

Intent(this, Page2::class.java)

Example -

val intent = Intent(this, NextActivity::class.java)
// To pass any data to next activity
intent.putExtra("keyIdentifier", value)
// start your next activity
startActivity(intent)