Nice to meet Kotlin
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This document introduces the Kotlin programming language, covering its features such as extension methods, lambda expressions, and domain-specific languages (DSLs). It provides code examples demonstrating how to implement these features in Kotlin compared to Java. Additionally, it includes information about application development using Kotlin and provides contact information for the author.
![Hello Kotlin!
fun main(args: Array<String>) {
println("Hello World!!")
}
public class Main {
public static void main(String[] args) {
System.out.println("Hello World!!");
}
}](https://image.slidesharecdn.com/k0yjprdsbypjdek7mhq1-signature-f6c5b4d01a8a86f0736e91f0718f71d03271a29c4ab2ef0db102e8aeae164da7-poli-171021054648/85/Nice-to-meet-Kotlin-2-320.jpg)
Nice to meet Kotlin
- 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!!"); } }
- 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)
- 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 [email protected]