Kotlin Multiplatform: Share Code Across Platforms

Kotlin Multiplatform Guide

Write once, run on every platform.

The Java Foundation

To understand Kotlin Multiplatform, it helps to understand the platform it was born from. Java follows a bytecode > JVM > machine instructions pipeline, achieving its famous write-once-run-anywhere promise. Source code compiles to platform-independent bytecode, which the Java Virtual Machine then translates into native machine instructions at runtime.

The JDK (Java Development Kit) includes development tools such as the compiler plus the JVM itself, while the JRE (Java Runtime Environment) provides only what is needed to run compiled Java applications. For development you need the JDK; for deployment you may only need the JRE.

Java Compared to Other Languages

Java vs Python: Java is statically typed, catching errors at compile time rather than runtime. It generally delivers higher performance thanks to JIT compilation, and the language maintains strong backwards compatibility across versions, making long-lived enterprise codebases viable.

Java vs JavaScript: Java is multithreaded with true parallel execution, whereas JavaScript relies on a single-threaded event loop. Java is compiled (to bytecode), while JavaScript is traditionally interpreted (though modern engines use JIT compilation). These distinctions make Java better suited for CPU-intensive backend services and JavaScript for event-driven I/O.