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staffolis's solution

to Resistor Color in the Java Track

Published at Feb 24 2021 · 0 comments
Test suite

Resistors have color coded bands, where each color maps to a number. The first 2 bands of a resistor have a simple encoding scheme: each color maps to a single number.

These colors are encoded as follows:

  • Black: 0
  • Brown: 1
  • Red: 2
  • Orange: 3
  • Yellow: 4
  • Green: 5
  • Blue: 6
  • Violet: 7
  • Grey: 8
  • White: 9

Mnemonics map the colors to the numbers, that, when stored as an array, happen to map to their index in the array: Better Be Right Or Your Great Big Values Go Wrong.

More information on the color encoding of resistors can be found in the Electronic color code Wikipedia article


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


Running the tests

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

$ gradle test

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.


Maud de Vries, Erik Schierboom https://github.com/exercism/problem-specifications/issues/1458

Submitting Incomplete Solutions

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


import org.junit.Before;
import org.junit.Test;
import org.junit.Ignore;

import static org.junit.Assert.assertEquals;

public class ResistorColorTest {

    private ResistorColor resistorColor;

    public void setup() {
        resistorColor = new ResistorColor();

    public void testBlackColorCode() {
        String input = "black";
        int expected = 0;

        assertEquals(expected, resistorColor.colorCode(input));

    @Ignore("Remove to run test")
    public void testWhiteColorCode() {
        String input = "white";
        int expected = 9;

        assertEquals(expected, resistorColor.colorCode(input));

    @Ignore("Remove to run test")
    public void testOrangeColorCode() {
        String input = "orange";
        int expected = 3;

        assertEquals(expected, resistorColor.colorCode(input));

    @Ignore("Remove to run test")
    public void testColors() {
        String[] expected = {"black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "grey", "white"};

        assertEquals(expected, resistorColor.colors());
import java.util.Arrays;

class ResistorColor {
    int colorCode(String color) {
        String [] colors = colors();
        return Arrays.asList(colors).indexOf(color);

    String[] colors() {
        return new String[]{"black","brown","red","orange","yellow","green","blue","violet","grey","white"};

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?
  • Are there new concepts here that you could read more about to improve your understanding?