From Java To Kotlin - Your Cheat Sheet For Java To Kotlin
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README.md

FromJavaToKotlin

From Java To Kotlin

Mindorks Mindorks Community

From Java To Kotlin - Your Cheat Sheet For Java To Kotlin

中文支持

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

final String name = null;
String otherName;
otherName = null;

Kotlin

val name : String? = null
var otherName : String?
otherName = null

Java

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

Kotlin

val length = text?.length

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+=2) { }

for (String item : collection) { }

for (Map.Entry<String, String> entry: map.entrySet()) { }

Kotlin

for (i in 1..10) { }

for (i in 1..10 step 2) {}

for (item in collection) {}

for ((key, value) in map) {}

Java

final List<Integer> listOfNumber = Arrays.asList(1, 2, 3, 4);

final Map<Integer, String> keyValue = new HashMap<Integer, String>();
map.put(1, "Amit");
map.put(2, "Ali");
map.put(3, "Mindorks");

Kotlin

val listOfNumber = listOf(1, 2, 3, 4)
val keyValue = mapOf(1 to "Amit",
                     2 to "Ali",
                     3 to "Mindorks")

Java

for (Car car : cars) {
  System.out.println(car.speed);
}

for (Car car : cars) {
  if(cars.speed > 100) {
    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 function

fun 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 function

fun 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 there

object 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(val name: String, val 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);

Kotlin

fun Int.triple(): Int {
  return this * 3
}

var result = 3.triple()

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License

   Copyright (C) 2017 MINDORKS NEXTGEN PRIVATE LIMITED

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

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