From Java To Kotlin - Your Cheat Sheet For 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 = nullJava
if(text != null){
int length = text.length();
}Kotlin
text?.let {
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 CarJava
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<String, String> 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<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");
// Java 9
final List<Integer> listOfNumber = List.of(1, 2, 3, 4);
final Map<Integer, String> keyValue = Map.of(1, "Amit",
2, "Ali",
3, "Mindorks");Kotlin
val listOfNumber = listOf(1, 2, 3, 4)
val keyValue = 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 function
fun getScore(): Int = scoreJava
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 * valueJava
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(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);Kotlin
fun Int.triple(): Int {
return this * 3
}
var result = 3.triple()- Support by clicking the ⭐ button on the upper right of this page. ✌️
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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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