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from-java-to-kotlin
Your interactive cheat sheet for the Java → Kotlin transition — every concept, side by side, with the 'why' noted.
KotlinJavaDocs
High-level design
A Java → Kotlin reference organised as a cheat sheet — each row shows the Java way next to the idiomatic Kotlin way, so the migration is a lookup, not a memorisation exercise.
Basics
printing, variables, null-safety
↓
Strings
templates, multiline, substring
↓
Control flow
when, ranges, for-loops, smart casts
↓
Collections
listOf, filter, sorting, destructuring
↓
Classes & objects
data class, object, companion, lateinit
↓
Advanced
generics, extension functions
Low-level design
The thesis: Kotlin didn't add features so much as make Java's boilerplate patterns first-class.
- –A ~30-line POJO becomes a one-line data class — the single biggest productivity win
- –Null-safety is the headline: non-null by default, opt in with ?, so whole classes of NPEs become impossible to write
- –switch → when (an expression), instanceof + cast → is + smart cast, static utils → extension functions