From|From Java to Kotlin FromJavatoKotlin

为什么80%的码农都做不了架构师？>>>
文章图片

From Java To Kotlin

Java

System.out.print("Amit Shekhar"); System.out.println("Amit Shekhar");

Kotlin

print("Amit Shekhar") println("Amit Shekhar")

Java

String name = "Amit Shekhar"; final String name = "Amit Shekhar";

Kotlin

var name = "Amit Shekhar" val name = "Amit Shekhar"

Java

String otherName; otherName = null;

Kotlin

var otherName : String? otherName = null

Java

if(text != null){ int length = text.length(); }

Kotlin

text?.let { val length = text.length }

【From|From Java to Kotlin】Java

String firstName = "Amit"; String lastName = "Shekhar"; String message = "My name is: " + firstName + " " + lastName;

Kotlin

val firstName = "Amit" val lastName = "Shekhar" val message = "My name is: $firstName $lastName"

Java

String text = "First Line\n" + "Second Line\n" + "Third Line";

Kotlin

val text = """ |First Line |Second Line |Third Line """.trimMargin()

Java

String text = x > 5 ? "x > 5" : "x <= 5";

Kotlin

val text = if (x > 5) "x > 5" else "x <= 5"

Java

if(object instanceof Car){ } Car car = (Car) object;

Kotlin

if (object is Car) { } var car = object as Car

Java

if(object instanceof Car){ Car car = (Car) object; }

Kotlin

if (object is Car) { var car = object // smart casting }

Java

if(score >= 0 && score <= 300 ){}

Kotlin

if (score in 0..300) { }

Java

int score = // some score; String grade; switch (score) { case 10: case 9: grade = "Excellent"; break; case 8: case 7: case 6: grade = "Good"; break; case 5: case 4: grade = "Ok"; break; case 3: case 2: case 1: grade = "Fail"; break; default: grade = "Fail"; }

Kotlin

var score = // some score var grade = when (score) { 9, 10 -> "Excellent" in 6..8 -> "Good" 4, 5 -> "Ok" in 1..3 -> "Fail" else -> "Fail" }

Java

for (int i = 1; i <= 10 ; i++) { }for (int i = 1; i < 10 ; i++) { }for (int i = 10; i >= 0 ; i--) { }for (int i = 1; i <= 10 ; i+=2) { }for (int i = 10; i >= 0 ; i-=2) { }for (String item : collection) { }for (Map.Entry entry: map.entrySet()) { }

Kotlin

for (i in 1..10) { }for (i in 1 until 10) { }for (i in 10 downTo 0) { }for (i in 1..10 step 2) {}for (i in 10 downTo 1 step 2) {}for (item in collection) {}for ((key, value) in map) {}

Java

final List listOfNumber = Arrays.asList(1, 2, 3, 4); final Map keyValue = https://www.it610.com/article/new HashMap(); map.put(1, "Amit"); map.put(2, "Ali"); map.put(3, "Mindorks"); // Java 9 final List listOfNumber = List.of(1, 2, 3, 4); final Map keyValue = https://www.it610.com/article/Map.of(1,"Amit", 2, "Ali", 3, "Mindorks");

Kotlin

val listOfNumber = listOf(1, 2, 3, 4) val keyValue = https://www.it610.com/article/mapOf(1 to"Amit", 2 to "Ali", 3 to "Mindorks")

Java

// Java 7 and below for (Car car : cars) { System.out.println(car.speed); }// Java 8+ cars.forEach(car -> System.out.println(car.speed)); // Java 7 and below for (Car car : cars) { if(car.speed > 100) { System.out.println(car.speed); } }// Java 8+ cars.stream().filter(car -> car.speed > 100).forEach(car -> System.out.println(car.speed));

Kotlin

cars.forEach { println(it.speed) }cars.filter{ it.speed > 100 } .forEach { println(it.speed)}

Java

void doSomething() { // logic here }

Kotlin

fun doSomething() { // logic here }

Java

int getScore() { // logic here return score; }

Kotlin

fun getScore(): Int { // logic here return score }// as a single-expression functionfun getScore(): Int = score

Java

int getScore(int value) { // logic here return 2 * value; }

Kotlin

fun getScore(value: Int): Int { // logic here return 2 * value }// as a single-expression functionfun getScore(value: Int): Int = 2 * value

Java

public class Utils {private Utils() { // This utility class is not publicly instantiable }public static int getScore(int value) { return 2 * value; }}

Kotlin

class Utils private constructor() {companion object {fun getScore(value: Int): Int { return 2 * value }} }// other way is also thereobject Utils {fun getScore(value: Int): Int { return 2 * value }}

Java

public class Developer {private String name; private int age; public Developer(String name, int age) { this.name = name; this.age = age; }public String getName() { return name; }public void setName(String name) { this.name = name; }public int getAge() { return age; }public void setAge(int age) { this.age = age; }@Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Developer developer = (Developer) o; if (age != developer.age) return false; return name != null ? name.equals(developer.name) : developer.name == null; }@Override public int hashCode() { int result = name != null ? name.hashCode() : 0; result = 31 * result + age; return result; }@Override public String toString() { return "Developer{" + "name='" + name + '\'' + ", age=" + age + '}'; } }

Kotlin

data class Developer(var name: String, var age: Int)

Java

public class Utils {private Utils() { // This utility class is not publicly instantiable }public static int triple(int value) { return 3 * value; }}int result = Utils.triple(3);