تلخيص الإختلافات بين لغة كوتلن وجافا

System.out.print("Abanoub Hanna");
System.out.println("Abanoub Hanna");

print("Abanoub Hanna")
println("Abanoub Hanna")

String name = "Abanoub Hanna";
final String name = "Abanoub Hanna";

var name = "Abanoub Hanna"
val name = "Abanoub Hanna"

String otherName;
otherName = null;

var otherName : String?
otherName = null

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

text?.let {
    val length = text.length
}
// or simply
val length = text?.length

String firstName = "Abanoub";
String lastName = "Hanna";
String message = "My name is: " + firstName + " " + lastName;

val firstName = "Abanoub"
val lastName = "Hanna"
val message = "My name is: $firstName $lastName"

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

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

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

String message = null;
log(message != null ? message : "");

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

val message: String? = null
log(message ?: "")

final int andResult  = a & b;
final int orResult   = a | b;
final int xorResult  = a ^ b;
final int rightShift = a >> 2;
final int leftShift  = a << 2;
final int unsignedRightShift = a >>> 2;
Logical Operators (Kotlin)
val andResult  = a and b
val orResult   = a or b
val xorResult  = a xor b
val rightShift = a shr 2
val leftShift  = a shl 2
val unsignedRightShift = a ushr 2

if (object instanceof Car) {
}
Car car = (Car) object;
Check the type and casting (Kotlin)
if (object is Car) {
}
var car = object as Car

// if object is null
var car = object as? Car // var car = object as Car?

if (object instanceof Car) {
   Car car = (Car) object;
}
Check the type and casting (implicit) (Kotlin)
if (object is Car) {
   var car = object // smart casting
}

// if object is null
if (object is Car?) {
   var car = object // smart casting, car will be null
}

if (score >= 0 && score <= 300) { }
Multiple conditions (Kotlin)
if (score in 0..300) { }

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";
}

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

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()) { }
For-loops (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) { }

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

final Map keyValue = new HashMap();
map.put(1, "Abanoub");
map.put(2, "Kerellos");
map.put(3, "Hesham");

// Java 9
final List listOfNumber = List.of(1, 2, 3, 4);

final Map keyValue = Map.of(1, "Abanoub",
                            2, "Kerellos",
                            3, "Hesham");

val listOfNumber = listOf(1, 2, 3, 4)
val keyValue = mapOf(1 to "Abanoub",
                     2 to "Kerellos",
                     3 to "Hesham")

// 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));

cars.forEach {
    println(it.speed)
}

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

// kotlin 1.1+
cars.stream().filter { it.speed > 100 }.forEach { println(it.speed)}
cars.parallelStream().filter { it.speed > 100 }.forEach { println(it.speed)}

String[] splits = "param=car".split("=");
String param = splits[0];
String value = splits[1];

val (param, value) = "param=car".split("=")

void doSomething() {
   // logic here
}

fun doSomething() {
   // logic here
}

void doSomething(int... numbers) {
   // logic here
}

fun doSomething(vararg numbers: Int) {
   // logic here
}

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

fun getScore(): Int {
   // logic here
   return score
}

// as a single-expression function

fun getScore(): Int = score

// even simpler (type will be determined automatically)

fun getScore() = score // return-type is Int

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

fun getScore(value: Int): Int {
   // logic here
   return 2* value
}

// as a single-expression function
fun getScore(value: Int): Int = 2 * value

// even simpler (type will be determined automatically)

fun getScore(value: Int) = 2 * value // return-type is int

public class Utils {

    private Utils() {
      // This utility class is not publicly instantiable
    }

    public static int getScore(int value) {
        return 2 * value;
    }

}

class Utils private constructor() {

    companion object {

        fun getScore(value: Int): Int {
            return 2 * value
        }

    }
}

// another way

object Utils {

    fun getScore(value: Int): Int {
        return 2 * value
    }

}

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 +
                '}';
    }
}

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

public class Developer implements Cloneable {

    private String name;
    private int age;

    public Developer(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return (Developer)super.clone();
    }
}

// cloning or copying
Developer dev = new Developer("Mindorks", 30);
try {
    Developer dev2 = (Developer) dev.clone();
} catch (CloneNotSupportedException e) {
    // handle exception
}

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

// cloning or copying
val dev = Developer("Mindorks", 30)
val dev2 = dev.copy()
// in case you only want to copy selected properties
val dev2 = dev.copy(age = 25)

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);

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

var result = 3.triple()

Person person;

internal lateinit var person: Person

public enum Direction {
        NORTH(1),
        SOUTH(2),
        WEST(3),
        EAST(4);

        int direction;

        Direction(int direction) {
            this.direction = direction;
        }

        public int getDirection() {
            return direction;
        }
    }

enum class Direction constructor(direction: Int) {
    NORTH(1),
    SOUTH(2),
    WEST(3),
    EAST(4);

    var direction: Int = 0
        private set

    init {
        this.direction = direction
    }
}

List profiles = loadProfiles(context);
Collections.sort(profiles, new Comparator() {
    @Override
    public int compare(Profile profile1, Profile profile2) {
        if (profile1.getAge() > profile2.getAge()) return 1;
        if (profile1.getAge() < profile2.getAge()) return -1;
        return 0;
    }
});

val profile = loadProfiles(context)
profile.sortedWith(Comparator({ profile1, profile2 ->
    if (profile1.age > profile2.age) return@Comparator 1
    if (profile1.age < profile2.age) return@Comparator -1
    return@Comparator 0
}))

 AsyncTask task = new AsyncTask() {
    @Override
    protected Profile doInBackground(Void... voids) {
        // fetch profile from API or DB
        return null;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // do something
    }
};

val task = object : AsyncTask() {
    override fun doInBackground(vararg voids: Void): Profile? {
        // fetch profile from API or DB
        return null
    }

    override fun onPreExecute() {
        super.onPreExecute()
        // do something
    }
}