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kotlin/hello-world/README.md

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+# Hello World
+
+Write a function that greets the user by name, or by saying "Hello, World!" if no name is given.
+
+["Hello, World!"](http://en.wikipedia.org/wiki/%22Hello,_world!%22_program) is the traditional first program for beginning programming in a new language.
+
+**Note:** You can skip this exercise by running:
+
+    exercism skip $LANGUAGE hello-world
+
+## Specification
+
+Write a `Hello World!` function that can greet someone given their name.
+The function should return the appropriate greeting.
+
+For an input of "Alice", the response should be "Hello, Alice!".
+
+If a name is not given, the response should be "Hello, World!"
+
+## Test-Driven Development
+
+As programmers mature, they eventually want to test their code.
+
+Here at Exercism we simulate [Test-Driven Development](http://en.wikipedia.org/wiki/Test-driven_development) (TDD), where you write your tests before writing any functionality. The simulation comes in the form of a pre-written test suite, which will signal that you have solved the problem.
+
+It will also provide you with a safety net to explore other solutions without breaking the functionality.
+
+### A typical TDD workflow on Exercism:
+
+1. Run the test file and pick one test that's failing.
+2. Write some code to fix the test you picked.
+3. Re-run the tests to confirm the test is now passing.
+4. Repeat from step 1.
+5. Submit your solution (`exercism submit /path/to/file`)
+
+## Instructions
+
+Submissions are encouraged to be general, within reason. Having said that, it's also important not to over-engineer a solution.
+
+It's important to remember that the goal is to make code as expressive and readable as we can. However, solutions to the hello-world exercise will not be reviewed by a person, but by rikki- the robot, who will offer an encouraging word.
+
+## Source
+
+This is an exercise to introduce users to using Exercism [http://en.wikipedia.org/wiki/%22Hello,_world!%22_program](http://en.wikipedia.org/wiki/%22Hello,_world!%22_program)
+
+## Submitting Incomplete Problems
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+

kotlin/hello-world/build.gradle

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+buildscript {
+  ext.kotlin_version = '1.0.2'
+  repositories {
+    mavenCentral()
+  }
+  dependencies {
+    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+  }
+}
+
+apply plugin: 'kotlin'
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+
+  testCompile 'junit:junit:4.12'
+  testCompile "org.jetbrains.kotlin:kotlin-test-junit:$kotlin_version"
+}

kotlin/hello-world/src/main/kotlin/HelloWorld.kt

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+/**
+ * Simple HelloWorld singleton class as defined by the `Kotlin object keyword`.
+ * See: https://kotlinlang.org/docs/reference/object-declarations.html#object-declarations
+ *
+ * As an alternative one could create a class such as:
+ * ```
+ * class HelloWorld(name: String? = "Default Value") {
+ *     fun hello(): String {
+ *
+ *     }
+ * }
+ * ```
+ * Resulting in a call such as: `HelloWorld("Bob").hello()`
+ * See: https://kotlinlang.org/docs/reference/classes.html#constructors
+ *
+ * In Kotlin we make objects defined as nullable via the trailing `?`, if you try
+ * to assign a null value to any value that isn't nullable a compilation error is thrown.
+ * Kotlin makes sure you are accessing nullable values safely and provides null safe calls
+ * and the use of the elvis operator. See: https://kotlinlang.org/docs/reference/null-safety.html
+ *
+ * You may provide default values on methods, so if an argument is omitted the default is used.
+ * See: https://kotlinlang.org/docs/reference/functions.html#default-arguments
+ *
+ * Kotlin provides String interpolation to make String formatting simple.
+ * See: https://kotlinlang.org/docs/reference/idioms.html#string-interpolation
+ */
+object HelloWorld {
+    fun hello(name: String? = "Default Argument"): String {
+
+    }
+}

kotlin/hello-world/src/test/kotlin/HelloWorldTest.kt

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+import kotlin.test.assertEquals
+import org.junit.Test
+
+class HelloWorldTest {
+
+    @Test
+    fun helloNoName() {
+        assertEquals("Hello, World!", HelloWorld.hello())
+    }
+
+    @Test
+    fun helloBlankName() {
+        assertEquals("Hello, World!", HelloWorld.hello(""))
+        assertEquals("Hello, World!", HelloWorld.hello("    "))
+    }
+
+    @Test
+    fun helloNullName() {
+        //This isn't advised in Kotlin but demonstrates the null safety in Kotlin
+        assertEquals("Hello, World!", HelloWorld.hello(null))
+    }
+
+    @Test
+    fun helloSampleName() {
+        assertEquals("Hello, Alice!", HelloWorld.hello("Alice"))
+    }
+
+    @Test
+    fun helloAnotherSampleName() {
+        assertEquals("Hello, Bob!", HelloWorld.hello("Bob"))
+    }
+}