How does Kotlin differ from Java in terms of features and syntax?

Kotlin is a statically typed cross-platform programming language that was developed by JetBrains, the creators of the IntelliJ IDEA IDE, and it runs on the Java Virtual Machine (JVM). Kotlin has many similarities with Java as well as several differences in terms of features and syntax.

Here are some of the main differences between Kotlin and Java:

1. Null Safety: Kotlin has built-in null safety features that help eliminate the infamous NullPointerException errors. In Kotlin, a variable cannot hold a null value unless explicitly declared as nullable using the "?" symbol. This greatly reduces the chances of runtime errors related to null values as compared to Java.

Example:

// Kotlin
var name: String = "John Doe"
// This is incorrect in Kotlin and will not compile as "null" is not allowed as a value.
var age: Int = null 

// Java
String name = "John Doe";
// This is correct in Java and will compile
Integer age = null;

2. Extension Functions: Kotlin allows for the creation of extension functions, which means that you can add new functionality to classes without modifying their source code. This feature greatly improves code readability and reduces the amount of code needed to accomplish tasks.

Example:

// Kotlin
fun String.removeWhiteSpaces(): String {
    return this.replace(" ", "")
}

val word = "Kotlin is Awesome"
val result = word.removeWhiteSpaces() // "KotlinisAwesome"

// Java
public static String removeWhiteSpaces(String s) {
    return s.replace(" ", "");
}

String word = "Java is Awesome";
String result = removeWhiteSpaces(word); // "JavaisAwesome"

3. Data Classes: Kotlin provides a shorthand way of defining classes for which the primary purpose is to hold data. Data classes automatically generate getter and setter methods, a ‘toString()‘, ‘equals()‘, and ‘hashcode()‘ functions, which reduces boilerplate code and improves code readability.

Example:

// Kotlin
data class Employee(val name: String, val age: Int)

val emp = Employee("John", 30)
println(emp.name) // "John"

// Java
public class Employee {
    private String name;
    private int age;
    
    public Employee(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 String toString() {
        return "Employee{" +
                "name='" + name + ''' +
                ", age=" + age +
                '}';
    }
}

Employee emp = new Employee("John", 30);
System.out.println(emp.getName()); // "John"

4. Type Inference: Kotlin has a feature called "type inference", which allows the compiler to automatically identify the data type of variables based on the context they are used in. This makes the code more concise, and reduces the amount of boilerplate code.

Example:

// Kotlin
val name = "John Doe" // Compiler infers the type as String
val age = 30 // Compiler infers the type as Int

// Java
String name = "John Doe";
int age = 30;

5. Coroutines: Kotlin provides a feature called coroutines, which allows for asynchronous programming without the use of callbacks or additional threads. Coroutines simplify concurrent programming and make it easier to write clean, efficient, and maintainable code.

Overall, while Kotlin has many similarities with Java, it provides several features that are not available in Java. These features, including null safety, extension functions, data classes, type inference, and coroutines, make Kotlin a powerful and modern programming language that is gaining popularity among developers.