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to Resistor Color Duo in the Java Track

Published at May 15 2020 · 0 comments
Test suite

If you want to build something using a Raspberry Pi, you'll probably use resistors. For this exercise, you need to know two things about them:

  • Each resistor has a resistance value.
  • Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read. To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values. Each band has a position and a numeric value. For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.

In this exercise you are going to create a helpful program so that you don't have to remember the values of the bands. The program will take color names as input and output a two digit number, even if the input is more than two colors!

The band 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

From the example above: brown-green should return 15 brown-green-violet should return 15 too, ignoring the third color.


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/1464

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 ResistorColorDuoTest {
    private ResistorColorDuo resistorColorDuo;

    public void setup() {
        resistorColorDuo = new ResistorColorDuo();

    public void testBrownAndBlack() {
        String[] input = { "brown", "black" };
        int expected = 10;
        int actual = resistorColorDuo.value(input);

        assertEquals(expected, actual);

    @Ignore("Remove to run test")
    public void testBlueAndGrey() {
        String[] input = { "blue", "grey" };
        int expected = 68;
        int actual = resistorColorDuo.value(input);

        assertEquals(expected, actual);

    @Ignore("Remove to run test")
    public void testYellowAndViolet() {
        String[] input = { "yellow", "violet" };
        int expected = 47;
        int actual = resistorColorDuo.value(input);

        assertEquals(expected, actual);

    @Ignore("Remove to run test")
    public void testOrangeAndOrange() {
        String[] input = { "orange", "orange" };
        int expected = 33;
        int actual = resistorColorDuo.value(input);

        assertEquals(expected, actual);

    @Ignore("Remove to run test")
    public void testIgnoreAdditionalColors() {
        String[] input = { "green", "brown", "orange" };
        int expected = 51;
        int actual = resistorColorDuo.value(input);

        assertEquals(expected, actual);
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;

class ResistorColorDuo {
    private static Map<String, Number> COLOR_VALUES = initializeColorValues();
    private static Map<String, Number> initializeColorValues() {
        final Map<String, Number> colorValues = new HashMap<String, Number>();
        colorValues.put("black", 0);
        colorValues.put("brown", 1);
        colorValues.put("red", 2);
        colorValues.put("orange", 3);
        colorValues.put("yellow", 4);
        colorValues.put("green", 5);
        colorValues.put("blue", 6);
        colorValues.put("violet", 7);
        colorValues.put("grey", 8);
        colorValues.put("white", 9);
        return colorValues;

    int value(final String[] colors) {
        return Integer.parseInt(String.join("", Arrays.asList(colors).stream().map(s -> COLOR_VALUES.get(s)).map(n -> n.toString()).collect(Collectors.toList()).subList(0, 2)));

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