Kotlin vs Java · Kotlin Introduction in Kotlin | Kotlin

Kotlin vs Java

Same Program in Both Languages

A Java program needs a class and a public static void main method:

public class Main {
    public static void main(String[] args) {
        String name = "Asha";
        int age = 22;
        System.out.println("Hello " + name + ", you are " + age);
    }
}

Example

The Kotlin version is shorter: no class, no semicolons, types are inferred and values go straight into the string.

fun main() {
    val name = "Asha"
    val age = 22
    println("Hello $name, you are $age")
}

Output

Hello Asha, you are 22

Key Differences

Feature	Java	Kotlin
Semicolons	required	optional (normally omitted)
Null safety	any reference can be null	`String` can never be null, `String?` can
Variables	`int x = 5;` / `final`	`var x = 5` / `val x = 5`
Type inference	only `var` for locals (Java 10+)	everywhere
String formatting	`"Hi " + name`	`"Hi $name"` (string templates)
switch	`switch`	`when` (more powerful, is an expression)
Checked exceptions	yes	no
Primitive types	`int`, `double` + wrappers	only `Int`, `Double`; compiler picks the primitive
Data holders	class + getters/setters/equals (or records)	`data class` in one line

Tip: You do not have to choose one forever. Kotlin calls Java code and Java calls Kotlin code in the same project, so teams migrate old Android apps one file at a time.