Catching Kotlin

This talk was given at the Denver Droids Meetup.
http://www.meetup.com/DenverDroids/events/232743206/

Transcript

1. Catching Kotlin Brandon Davis
2. Why?
3. Why Not?
4. Features • Type inference • No primitives • “Object” is now “Any” • “void” is now “Unit” • Everything is final unless declared open • This causes problems with mocking for unit testing • https://github.com/nhaarman/mockito-kotlin
5. Converting from Java • Copy, Paste • Convert Java file to Kotlin
6. no modifier is public private protected internal is package private Visibility Modifiers public private protected no modifier is package private
7. Variables and Constants var i: Int = 0
 val j: Int = 0 int i = 0;
 final int j = 0;
8. Variables and Constants var i = 0
 val j = 0 int i = 0;
 final int j = 0;
9. Backing Properties resources.getString(R.string.first_name) getResources().getString(R.string.first_name);
10. Backing Properties textView.text = "This is my text” textView.setText("This is my text");
11. Methods fun isGreat(langName: String): Boolean {
 return isKotlin(langName)
 } public boolean isGreat(String langName) {
 return isKotlin(langName);
 }
12. Methods fun isGreat(langName: String) = isKotlin(langName) public boolean isGreat(String langName) {
 return isKotlin(langName);
 }
13. Methods fun updateTable(name: String, listener: NetworkListener = null) {
 //Do stuff
 } public void updateTable(String name) {
 updateTable(name, null);
 }
 
 public void updateTable(String name, NetworkListener listener) {
 //Do stuff
 }
14. Classes class MainClass(type: String) : BaseClass {
 private val type: String 
 
 init {
 this.type = type
 //Do stuff
 }
 } public class MainClass extends BaseClass {
 private String type;
 
 public MainClass(String type) {
 this.type = type;
 //Do stuff
 }
 }
15. Classes class MainClass(val type: String) : BaseClass {
 …
 } public class MainClass extends BaseClass {
 private String type;
 
 public MainClass(String type) {
 this.type = type;
 }
 }
16. Classes class CustomView : View, MyInterface {
 
 constructor(ctx: Context?) : super(ctx)
 
 constructor(ctx: Context?, attrs: AttributeSet?) : super(ctx, attrs) {
 myMethod()
 }
 } public class CustomView extends View implements MyInterface {
 public CustomView(Context ctx) {
 super(ctx);
 }
 
 public CustomView(Context ctx, AttributeSet attrs) {
 super(ctx, attrs);
 myMethod();
 }
 }
17. Expressions val value = if (isKotlin) {
 "Woohoo"
 } else {
 "Sad day"
 } String value;
 
 if (isKotlin()) {
 value = "Woohoo";
 } else {
 value = "Sad day";
 }
18. Expressions val myInt: Int = try {
 parseInt(input)
 } catch (e: Exception) {
 0
 } int myInt;
 
 try {
 myInt = parseInt(input);
 } catch (Exception e) {
 myInt = 0;
 }
19. Null Safety - ? var myString: String? = null
 myString?.replace("Foo", "Bar", true)
 
 var myOtherString = "FooBar"
 myOtherString.replace("Foo", "Bar", true) if (myString != null) {
 myString.replace("Foo", "Bar");
 }
20. Null Safety - ?: val myString = otherString? "Foo" ?: "Bar" String myString;
 if (otherString != null) {
 myString = "Foo";
 } else {
 myString = "Bar";
 }
21. Null Safety - let myString?.let {
 it.replace("Foo", "Bar")
 } if (myString != null) {
 myString.replace("Foo", "Bar");
 }
22. Null Safety - !! var myString = null
 val length = myString!!.length String myString = null;
 int length = myString.length();
23. Casts - as val activity = myClass as? Activity
 val resources = activity?.resources if (myClass instanceof Activity) {
 Resources resources = ((Activity) myClass).getResources();
 }
24. Casts - is if (myClass is Activity) {
 val resources = myClass.resources
 } if (myClass instanceof Activity) {
 Resources resources = ((Activity) myClass).getResources();
 }
25. Lambdas myButton.setOnClickListener(object : OnClickListener {
 override fun onClick(v: View) {
 //Do stuff
 }
 } myButton.setOnClickListener(new OnClickListener() {
 @Override
 public void onClick(View v) {
 //Do stuff
 }
 });
26. Lambdas myButton.setOnClickListener { //Do stuff } myButton.setOnClickListener(new OnClickListener() {
 @Override
 public void onClick(View v) {
 //Do stuff
 }
 });
27. Collections channelList?.flatMap { it.episodeList }?.map { it.delete() } if (channelList != null) {
 for (Channel channel : channelList) {
 for (Episode episode : channel.getEpisodeList()) {
 episode.delete();
 }
 }
 }
28. Collections ArrayList newList = new ArrayList();
 for (Channel channel : channelList) {
 if (channel.getTitle().startsWith("Fox")) {
 newList.add(channel);
 }
 } val channels = channelList.filter { it.title.startsWith("Fox") } 
 val channelsWithTitle = channelList.filterNot { it.title == null }
 val channel = channelList.find { it.title.equals("Channel 1") }
29. But wait… there’s more
30. Data Classes public class Person {
 private String firstName;
 
 public String getFirstName() {
 return firstName;
 }
 
 public void setFirstName(String firstName){
 this.firstName=firstName;
 }
 
 @Override
 public boolean equals(Object obj) {…}
 
 @Override
 public int hashCode() {…}
 
 @Override
 public String toString() {…}
 }
31. Data Classes data class Person(val firstName: String)
32. Kotlin Android Extensions public class MyActivity extends Activity {
 @Override
 public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 
 TextView someText = (TextView) findViewById(R.id.text_view);
 someText.setText("Hello, world!");
 }
 }
33. Kotlin Android Extensions import kotlinx.android.synthetic.main.activity_main.text_view
 
 class MyActivity : Activity() {
 override fun onCreate(savedInstanceState: Bundle?) {
 super.onCreate(savedInstanceState)
 setContentView(R.layout.activity_main)
 text_view.setText(“Hello, world!")
 }
 }
34. Setup
35. Setup buildscript {
 repositories {
 jcenter()
 }
 dependencies {
 classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:1.0.3'
 classpath 'org.jetbrains.kotlin:kotlin-android-extensions:1.0.3'
 }
 } dependencies {
 compile 'org.jetbrains.kotlin:kotlin-stdlib:1.0.3' testCompile 'org.jetbrains.kotlin:kotlin-test-junit:1.0.3'
 }
36. Setup sourceSets {
 test.java.srcDirs += 'src/test/kotlin'
 main.java.srcDirs += 'src/main/kotlin'
 }
37. Further Reading • Try Kotlin • Kotlin Documentation • Kotlin for Android Developers - Antonio Leiva • Interal memo on Kotlin at Square - Jake Wharton • How I fell in love with a programming language - Dan Kim • Making Safer Apps - Eric Young
38. Further Watching • Android Development with Kotlin - Jake Wharton • Advancing Android Development with the Kotlin Language - Jake Wharton
39. Go write some code! @xBrandonDavisx