NameJoiner.java

package com.google.ara.app.manager;

import java.util.List;

public class NameJoiner {

    private NameJoiner() {
    }

    public static String join(List<String> names, int index, String... separators) {
        if (names.size() == 0) {
            return "";
        }
        if (names.size() == 1) {
            return names.get(0);
        }
        StringBuilder sb = new StringBuilder();
        List<String> tail = names.subList(1, names.size());
        String separator = names.size() == 2
                ? separators[separators.length - 1]
                : separators[index % (separators.length - 1)];
        return sb
                .append(names.get(0))
                .append(separator)
                .append(join(tail, index + 1, separators))
                .toString();
    }
}

NameJoinerTest.java

package com.google.ara.app.manager;

import org.junit.Test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import static org.assertj.core.api.Assertions.assertThat;

public class NameJoinerTest {

    private final static String JOINER = ", ";
    private final static String FINAL_JOINER = " and ";

    private List<String> zeroModules = new ArrayList<>();
    private List<String> oneModule = Arrays.asList("13MP Camera");
    private List<String> twoModules = Arrays.asList("13MP Camera", "Harman Speaker");
    private List<String> manyModules = Arrays.asList("13MP Camera", "Harman Speaker", "Hi fi Speaker", "Micron Storage");

    @Test
    public void testZeroModuleNames() {
        assertThat(NameJoiner.join(zeroModules, 0, JOINER, FINAL_JOINER)).isEqualTo("");
    }

    @Test
    public void testOneModuleName() {
        assertThat(NameJoiner.join(oneModule, 0, JOINER, FINAL_JOINER)).isEqualTo("13MP Camera");
    }

    @Test
    public void testTwoModuleNames() {
        assertThat(NameJoiner.join(twoModules, 0, JOINER, FINAL_JOINER)).isEqualTo("13MP Camera and Harman Speaker");
    }

    @Test
    public void testManyModuleNames() {
        assertThat(NameJoiner.join(manyModules, 0, JOINER, FINAL_JOINER))
                .isEqualTo("13MP Camera, Harman Speaker, Hi fi Speaker and Micron Storage");
    }
}