MrGarri's solution

to Darts in the Java Track

Published at Apr 16 2019 · 2 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

Write a function that returns the earned points in a single toss of a Darts game.

Darts is a game where players throw darts to a target.

In our particular instance of the game, the target rewards with 4 different amounts of points, depending on where the dart lands:

• If the dart lands outside the target, player earns no points (0 points).
• If the dart lands in the outer circle of the target, player earns 1 point.
• If the dart lands in the middle circle of the target, player earns 5 points.
• If the dart lands in the inner circle of the target, player earns 10 points.

The outer circle has a radius of 10 units (This is equivalent to the total radius for the entire target), the middle circle a radius of 5 units, and the inner circle a radius of 1. Of course, they are all centered to the same point (That is, the circles are concentric) defined by the coordinates (0, 0).

Write a function that given a point in the target (defined by its `real` cartesian coordinates `x` and `y`), returns the correct amount earned by a dart landing in that point.

Setup

Go through the setup instructions for Java to install the necessary dependencies:

https://exercism.io/tracks/java/installation

Running the tests

You can run all the tests for an exercise by entering the following in your terminal:

``````\$ gradle test
``````

Use `gradlew.bat` if you're on Windows

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by removing the `@Ignore("Remove to run test")` annotation.

Source

Inspired by an exercise created by a professor Della Paolera in Argentina

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

DartsTest.java

``````import org.junit.Ignore;
import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class DartsTest {

@Test
public void testDartOutsideTarget() {
Darts darts = new Darts(-9, 9);
assertEquals(0, darts.score());
}

@Ignore("Remove to run test")
@Test
public void testDartLandsOnBorderOfTarget() {
Darts darts = new Darts(0, 10);
assertEquals(1, darts.score());
}

@Ignore("Remove to run test")
@Test
public void testDartLandsInOuterCircle() {
Darts darts = new Darts(4, 4);
assertEquals(1, darts.score());
}

@Ignore("Remove to run test")
@Test
public void testDartLandsInBorderBetweenOuterAndMiddleCircles() {
Darts darts = new Darts(5, 0);
assertEquals(5, darts.score());
}

@Ignore("Remove to run test")
@Test
public void testDartLandsOnMiddleOfCircle() {
Darts darts = new Darts(0.8, -0.8);
assertEquals(5, darts.score());
}

@Ignore("Remove to run test")
@Test
public void testDartLandsOnBorderBetweenMiddleAndInnerCircles() {
Darts darts = new Darts(0, -1);
assertEquals(10, darts.score());
}

@Ignore("Remove to run test")
@Test
public void testDartLandsInTheInnerCircle() {
Darts darts = new Darts(-0.1, -0.1);
assertEquals(10, darts.score());
}

}``````
``````import java.awt.geom.Point2D;

class Darts {

private final double x;
private final double y;
private final Point2D CENTER = new Point2D.Double(0, 0);

Darts(double x, double y) {
this.x = x;
this.y = y;
}

int score() {
Point2D hit = new Point2D.Double(x, y);

if (hit.distance(CENTER) > 10)
return 0;
else if (hit.distance(CENTER) > 5)
return 1;
else if (hit.distance(CENTER) > 1)
return 5;
else
return 10;
}

}``````

I starred this for the use of `Point2D` and its `distance()` method. I also used the name `hit` in my solution; I think it's a great name that expresses the idea it represents very well. Very good choices, if I say so myself. ;)

I made the same comment on other solutions but will repeat here so you don't have to hunt it down: The API suggests that `Dart` is an immutable class so I think it's a better choice to calculate the score in the constructor instead and have a final field `score` rather than keeping the x and y coordinates around longer than they really need to be.

I've seen this logic in other solutions and I think the aversion to the `<=` is costing some clarity. I find it a bit disconcerting to see the ring distance boundaries and the corresponding scores in separate sections of the if-else-if statements. At first glance, it appears to be incongruent with the requirements and I had to take a few seconds to go over the logic to make sure I wasn't getting cross-eyed.

On the other hand, I think using <= is more straightforward and the code aligns well with the requirement statement

``````if (distance <= 1)
score = 10
else if (distance <= 5)
score = 5
else if (distance <= 10)
score = 1
else
score = 0
``````

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?