Add hello-world exercise

This implementation does not generate a test suite based on the json
meta the hello-world exercise.
See https://github.com/exercism/todo/issues/13

Fixes https://github.com/exercism/todo/issues/35

config.json

@@ -34,7 +34,8 @@
     "octal",
     "luhn",
     "pig-latin",
-    "pascals-triangle"
+    "pascals-triangle",
+    "hello-world"
   ],
   "deprecated": [
   ],

hello-world/GETTING_STARTED.md

@@ -0,0 +1,156 @@
+# Getting Started
+
+These exercises lean on Test-Driven Development (TDD), but they're not an exact match.
+
+The following steps assume that you are in the base directory of the exercise.
+
+You must have `gradle` installed.
+
+## Step 1
+
+Run the test suite. It's written using the JUnit framework, and can be run with gradle:
+
+```sh
+$ gradle test
+```
+
+This will fail, complaining that there is no method called `hello` for the `HelloWorld` class.
+
+To fix the error, open `src/main/java/HelloWorld.java` and add a `hello` method that returns a `String`.
+The method can return an empty string `""` for now:
+
+```java
+public class HelloWorld {
+    public static String hello() {
+        return "";
+    }
+}
+```
+
+## Step 2
+
+Run the tests again. It will give you a new error, since now the method exists, but the tests are expects the
+method to accept one argument as input, a name.
+
+The errors will look something like:
+
+```
+$ gradle test
+:compileJava
+:processResources UP-TO-DATE
+:classes
+:compileTestJava
+/exercism/exercises/java/hello-world/src/test/java/HelloWorldTest.java:9: error: method hello in class HelloWorld cannot be applied to given types;
+        assertEquals("Hello, World!", HelloWorld.hello(""));
+                                                ^
+  required: no arguments
+  found: String
+  reason: actual and formal argument lists differ in length
+
+  ...
+
+4 errors
+:compileTestJava FAILED
+
+FAILURE: Build failed with an exception.
+
+* What went wrong:
+Execution failed for task ':compileTestJava'.
+> Compilation failed; see the compiler error output for details.
+```
+
+### Fixing the Error
+
+To fix it, open `src/main/java/HelloWorld.java` and add a `name` to the method the signature:
+
+```java
+public class HelloWorld {
+    public static String hello(String name) {
+        return "";
+    }
+}
+```
+
+Now the `hello` method accepts a `name` as an input.
+
+### Understanding Test Failures
+
+Test failures will either be compilation errors or test failures. So far, we've been dealing with compilation
+errors. Once our test and main code successful compile, `gradle` will run the actual test suite.
+
+## Step 3
+
+Run the tests again. You'll notice that the gradle output passes the `:compileTestJava` phase and fails
+at the `:test` phase.
+
+The errors will look something like:
+
+```
+$ gradle test
+:compileJava
+:processResources UP-TO-DATE
+:classes
+:compileTestJava
+:processTestResources UP-TO-DATE
+:testClasses
+:test
+
+HelloWorldTest > helloNoName FAILED
+    org.junit.ComparisonFailure at HelloWorldTest.java:9
+
+...
+
+3 tests completed, 3 failed
+:test FAILED
+```
+
+These are actual test failures. It means that both our main and test java code is running but the test is
+expecting one outcome, but getting another.
+
+Open `src/test/java/HelloWorldTest.java` and go to line 9.
+
+```java
+assertEquals("Hello, World!", HelloWorld.hello(""));
+```
+
+The test is expecting that `hello` returns "Hello, World!", when given an empty string (`""`) as input.
+The easiest way to make the test pass is to return `"Hello, World!"` instead of `"".
+
+```java
+public class HelloWorld {
+    public static String hello(String name) {
+        return "Hello, World!";
+    }
+}
+```
+
+## Wash, Rinse, Repeat
+
+Run the tests again.
+
+If it fails you're going to need to read the error message carefully to figure out what went wrong, fix the problem
+in the main code, and then try again until all the tests pass.
+
+```
+$ gradle test
+:compileJava
+:processResources UP-TO-DATE
+:classes
+:compileTestJava
+:processTestResources UP-TO-DATE
+:testClasses
+:test
+
+BUILD SUCCESSFUL
+```
+
+## Submit
+
+When everything is passing, you can submit your code with the following command:
+
+```
+$ exercism submit src/main/java/HelloWorld.java
+```
+
+
+

hello-world/build.gradle

@@ -0,0 +1,12 @@
+apply plugin: "java"
+apply plugin: "eclipse"
+apply plugin: "idea"
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  testCompile "junit:junit:4.10"
+}
+

hello-world/src/example/java/HelloWorld.java

@@ -0,0 +1,9 @@
+public class HelloWorld {
+    public static String hello(String name) {
+        if (name == null || name.isEmpty()) {
+            return "Hello, World!";
+        }
+
+        return String.format("Hello, %s!", name);
+    }
+}

hello-world/src/main/java/HelloWorld.java

@@ -0,0 +1,2 @@
+public class HelloWorld {
+}

hello-world/src/test/java/HelloWorldTest.java

@@ -0,0 +1,22 @@
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class HelloWorldTest {
+
+    @Test
+    public void helloNoName() {
+        assertEquals("Hello, World!", HelloWorld.hello(""));
+        assertEquals("Hello, World!", HelloWorld.hello(null));
+    }
+
+    @Test
+    public void helloSampleName() {
+        assertEquals("Hello, Alice!", HelloWorld.hello("Alice"));
+    }
+
+    @Test
+    public void helloAnotherSampleName() throws Exception {
+        assertEquals("Hello, Bob!", HelloWorld.hello("Bob"));
+    }
+}

settings.gradle

@@ -9,6 +9,7 @@ include 'etl'
 include 'gigasecond'
 include 'grade-school'
 include 'hamming'
+include 'hello-world'
 include 'luhn'
 include 'meetup'
 include 'nucleotide-count'