Introduce a Kotlin language and final I develope a simple app of movies introduction by Lotlin and java.

1. Introduction of Kotlin
Language
Jieyi Wu
2017.04.20

2. Hello Kotlin!
fun main(args: Array<String>) {
println("Hello World!!")
}
public class Main {
public static void main(String[] args) {
System.out.println("Hello World!!");
}
}

3. 1. Extension Method

4. “
Throw away your java Utility Class !!
FileUtils AppUtils
TimeUtils

5. Utilities Class in Java
public final class AppUtils {
private AppUtils() {
throw new UnsupportedOperationException("u can't instantiate me...");
}
public static String getAppName(Context context) {
return getAppName(context, context.getPackageName());
}
public static String getAppName(Context context, String packageName) {
if (isSpace(packageName)) return null;
try {
PackageManager pm = context.getPackageManager();
PackageInfo pi = pm.getPackageInfo(packageName, 0);
return pi == null ? null : pi.applicationInfo.loadLabel(pm).toString();
} catch (PackageManager.NameNotFoundException e) {
e.printStackTrace();
return null;
}
}
……
}
public class MyActivity extends Activity {
@Override
protected void onCreate(@Nullable Bundle
savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
AppUtils.getAppIcon(this);
}
}
Define
Usage

6. Extension Method in Kotlin
inline fun Context.getAppName(): String = this.packageName
inline fun Context.getAppIcon(): Drawable? = this.getAppIcon(this.packageName)
inline fun Context.getAppIcon(packageName: String): Drawable? {
if (isSpace(packageName)) return null
try {
val pm = this.packageManager
val pi = pm.getPackageInfo(packageName, 0)
return if (null == pi) null else pi.applicationInfo.loadIcon(pm)
}
catch (e: PackageManager.NameNotFoundException) {
e.printStackTrace()
return null
}
}
Define
Usage
class App: Application() {
override fun onCreate() {
super.onCreate()
// equal `this.getAppIcon()`
getAppIcon()
}
}

7. 2. Lambdas

8. “✘Find the restrooms which are the distance
of 5 kilometers from me and public Toilet.
The restroom list is sorted and the restroom
name only.
data class Toilet(val id: Int,
val name: String,
val quantity: Int,
val type: Int,
val isPublic: Boolean,
val distance: Double)

9. Thinking
5 km Public Sorted Name

10. Java Code
List<Toilet> newList = new ArrayList<>();
List<String> resultList = new ArrayList<>();
list.forEach(toilet -> {
if (5 >= toilet.getDistance() && toilet.isPublic()) {
newList.add(toilet);
}
});
newList.sort((o1, o2) -> (int) (o2.getDistance() - o1.getDistance()));
newList.forEach(toilet -> resultList.add(toilet.getName()));

11. Kotlin Code
listToliets.filter { it.distance > 5 }.
filterNot { it.isPublic }.
sortedWith(compareBy({ it.distance })).
map { it.name }.
orEmpty()

12. 3. DSL (Domain Specific
Language)

13. “✘Builder
✘Listener
✘Anko

14. DSL in Java
class Car {
private String name;
private double price;
private String model;
private int year;
private Car(String name, double price, String
model, int year) {
this.name = name;
this.price = price;
this.model = model;
this.year = year;
}
// getter and setter
// ...
}
static class Builder {
private String name;
private double price;
private String model;
private int year;
public Builder setName(String name) {
this.name = name;
return this;
}
public Builder setPrice(double price) {
this.price = price;
return this;
}
// ...
public Car build() {
return new Car(this.name, this.price, this.model,
this.year)
}
}
new Car.Builder()
.setName("Car")
.setPrice(12000)
.build();
Usage
Define

15. DSL in Kotlin
class Car(val name: String?, val price: Double, val model: String?, val year:
Int) {
private constructor(builder: Builder):
this(builder.name, builder.price, builder.model, builder.year)
companion object {
inline fun build(block: Builder.() -> Unit) =
Builder().apply(block).build()
}
internal class Builder() {
var name: String? = null
var price: Double = .0
var model: String? = null
var year: Int = 0
fun build() = Car(this)
}
}
val car = Car.build {
name = "CAR"
price = 1000.0
model = "BMW"
}
Usage
Define

16. Application
is developed
by Kotlin &
Java

19. thanks!
Any questions?
You can find me at
@Jieyi
jieyi.wu@colverlan.jp