Learn Comparing Kotlin and Java Syntax | Kotlin Foundations and Interoperability

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Before you begin writing Kotlin code as a Java developer, it's important to understand the main similarities and differences between the two languages, especially in their syntax, type system, and some of their unique features. Both Kotlin and Java are statically typed and run on the Java Virtual Machine (JVM), but Kotlin introduces a more concise syntax and additional language constructs that streamline development.

Start by comparing how you define classes, functions, and variables in both languages. In Java, you typically declare classes and methods with explicit visibility modifiers and type annotations. Kotlin, on the other hand, reduces boilerplate and uses type inference where possible, making code more concise.

SimpleClass.kt

SimpleClass.java


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package com.example

class Person(val name: String, var age: Int) {
    fun greet(): String {
        return "Hello, my name is $name and I am $age years old."
    }
}

fun main() {
    val person = Person("Alice", 30)
    println(person.greet())
}

Kotlin’s type system introduces two major enhancements over Java: type inference and nullability control. Type inference means you can often omit explicit type declarations when the compiler can determine the type from context. For example, when you write val person = Person("Alice", 30), Kotlin understands that person is of type Person without you needing to specify it. In Java, you must always declare the type: Person person = new Person("Alice", 30);.

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