Hello Java, again.

I foolishly thought that I couldn't learn anything from Java, but I can
(and should, probably). In this place I'll play a bit with java and see
if I can learn a few new things about it.

java/README.md

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# Java can surprise you
I thought I knew Java, I'd written code in it for a few years now, but I
was *wrong*. While I was able to solve a problem in Java, I didn't
really understand it, I had just developed enough mental workarounds to
make it appear so.
With this little project, I'll try to remedy this a bit. I have to write
more Java now, and I'd like to be able to say "I know Java" with
confidence.
Recently, I came across an interesting idea: to start playing with a
language using unit tests, so as to test your understanding of the
language and practicing testing at the same time. So I'll try this style
of playing on for size.
## Open questions
* output arguments
* string immutability
* copying/passing objects and primitives (when is it a copy, when a
  reference)

java/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>lp.java</groupId>
    <artifactId>understanding</artifactId>
    <version>0.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.8.2</version>
        </dependency>
    </dependencies>
</project>

java/src/test/java/understanding/TestOutputParameters.java

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package understanding;
import org.junit.Test;
import static org.junit.Assert.*;
/**
 * Documenting the behaviour of output parameters in Java.
 */
public class TestOutputParameters {
	// FIXME: The name already suggests that this should go in either a
	//        Strings class or in a separate ImmutableObjects class.
	//        However, because immutable objects probably behave
	//        differently than mutable objects especially in the context
	//        of output parameters, at least a note regarding their
	//        interactions should be retained.
	@Test
	public void stringsAreImmutable() {
		String input = "the thing";
		this.tryAssigningAStringArgument(input, "will not be assigned");
		assertEquals(input, "the thing");
	}
	
	public void tryAssigningAStringArgument(String s, String assignment) {
		s = assignment;
	}
	
	@Test
	public void aMethodCantChangeItsParameters() {
		int output = 0;
		this.increment(output);
		assertEquals(output, 0);
	}
	
	public void increment(int i) {
		i += 1;
	}
	
	@Test
	public void thisActsLikeAnOutputArgument() {
		SelfChangingObject selfChangingObject = new SelfChangingObject("hello");
		selfChangingObject.change();
		assertEquals(selfChangingObject.value, "bye");
	}
	
	private class SelfChangingObject {
		String value;
		SelfChangingObject(String value) {
			this.value = value;
		}
		void change() {
			this.value = "bye";
		}
	}
}