battleships

A simulation of the famous battleship board game

Architecture

Every software project should start with some thinking. So did this. Review the architecture

A quick intro to the Kotlin syntax

Function/Method syntax

fun hello(param1: String): String
 ^   ^     ^       ^        ^- return type
 |   |     |       |- parameter type
 |   |     |- parameter name
 |   |- function name
 |- function keyword

Variables

Kotlin is always strictly typed, but it's not necessary to add the type declaration to every element.

var foo = "bar" // a mutable variable of type String (the type is automatically inferred by the compiler)
var foo: String = "bar" // same as above, but ": String" is obsolete

val foo = "bar" // an immutable variable of type String (the type is automatically inferred by the compiler)
foo = "hello" // not possible, as immutable variables cannot be changed after initialization

var foo: String? = null // by default, variables in Kotlin cannot be null, unless suffixed with ?

Control flows

Kotlin makes use of functional and oo principles.

val list = listOf("A","B","C")
val c = list.find { it == "C" } // c is of type :String?, as find could return null

var ships: List<Ship?> = listOf(null, Ship("Curiser"))
println(ships[0]?.name) // prints null, due to the ? safecall
println(ships[0]!!.name) // throws an NPE, due to !! not-null assertion operator
println(ships[0].name) // does not compile, because list elements can be nullable
println(ships[1]?.name) // prints "Cruiser"

var ship: Ship?
[..] // more code
ship?.let { // same logic as with "if ship != null"
  // do something useful
}

Structures

The code makes some use of Pairs/Tuples. In Kotlin, it's very easy to create Pairs:

val foo = 0 to "Zero" // -> same as val foo = Pair<Int, String>(0, "Zero")

// with such, it's also straight forward to create lists:
val myList = listOf(
    0 to "Zero",
    1 to "One",
    2 to "Two",
    ...
)

// Pairs can also easily be destructed
val xy = x to y
val (a, b) = xy // a == x, b == y

A word on frameworks

I started this project with the Spring initializer, because I thought I might add a web-client to this. Due to missing time, I didn't do it yet. The game doesn't make any use of the Spring framework, but could be easily modified in the future. The Subscribers make it easy to sent game information to other clients.