package com.steveyg.hellokotlin; 
 
import android.os.Bundle; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.View; 
import android.view.Menu; 
import android.view.MenuItem; 
 
public class MainActivity extends AppCompatActivity { 
 
 @Override 
 protected void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.activity_main); 
 
 } 
} 

package com.steveyg.hellokotlin 
 
import android.os.Bundle 
import android.support.design.widget.FloatingActionButton 
import android.support.design.widget.Snackbar 
import android.support.v7.app.AppCompatActivity 
import android.support.v7.widget.Toolbar 
import android.view.View 
import android.view.Menu 
import android.view.MenuItem 
 
class MainActivity : AppCompatActivity() { 
 
 override fun onCreate(savedInstanceState: Bundle?) { 
  super.onCreate(savedInstanceState) 
  setContentView(R.layout.activity_main) 
 
 } 
} 

apply plugin: 'kotlin-android-extensions' 

<TextView 
 android:id="@+id/textview" 
 android:layout_width="wrap_content" 
 android:layout_height="wrap_content" /> 

import kotlinx.android.synthetic.main.content_main.* 

textview.text = "hello world"; 

package com.steveyg.hellokotlin.java; 
 
public class Demo { 
 public String getType(){ 
  return "Java"; 
 } 
 
} 

var demo = Demo(); 
textview.text = demo.type; 

package com.steveyg.hellokotlin.kotlin 
 
class KotlinDemo { 
 fun getType(): String{ 
  return "Kotlin"; 
 } 
} 

public String getKotlinType(){ 
 return new KotlinDemo().getType(); 
} 

textview.text = demo.kotlinType;