Join strings

@Test
public void join_a_list_of_strings () {

    List<String> cloudGroups = Lists.newArrayList(
            "Cirrus", "Alto", "Stratus",
            "Vertical Growth", "Special Clouds");

    String cloudGroupsJoined = Joiner.on(",").join(cloudGroups);

    assertEquals("Cirrus,Alto,Stratus,Vertical Growth,Special Clouds",
            cloudGroupsJoined);
}

Join strings skipping null

@Test
public void join_a_list_of_strings_skipping_null () {

    List<String> cloudGroups = Lists.newArrayList(
            "Cirrus", "Alto", null, null,
            "Stratus", "Vertical Growth", "Special Clouds", null);

    String cloudGroupsJoined = Joiner.on(",").skipNulls().join(cloudGroups);

    assertEquals("Cirrus,Alto,Stratus,"
            + "Vertical Growth,Special Clouds",
            cloudGroupsJoined);
}

Join strings replacing null

/**
 * Join a list of strings, add 'and' between each element,
 * replace null with '[unknown]'
 */
@Test
public void join_a_list_of_strings_replacing_null () {

    List<String> cloudGroups = Lists.newArrayList(
            "Cirrus", "Alto", null, null,
            "Stratus", "Vertical Growth", "Special Clouds", null);

    String cloudGroupsJoined = Joiner
            .on(" and ")
            .useForNull("[unknown]")
            .join(cloudGroups);

    assertEquals("Cirrus and Alto and [unknown] and [unknown] "
            + "and Stratus and Vertical Growth "
            + "and Special Clouds and [unknown]",
            cloudGroupsJoined);
}

Join map keys/values

@Test
public void join_key_values_map () {
    Multimap<String, String> clouds = ArrayListMultimap.create();

    clouds.put("Cirrus", "Cirrus");
    clouds.put("Cirrus", "Cirrostratus");
    clouds.put("Cirrus", "Cirrocumulus");

    clouds.put("Alto", "Altostratus");
    clouds.put("Alto", "Altocumulus");

    clouds.put("Stratus", "Stratus");
    clouds.put("Stratus", "Stratocumulus");
    clouds.put("Stratus", "Nimbostratus");

    clouds.put("Vertical Growth", "Cumulus");
    clouds.put("Vertical Growth", "Cumulonimbus");

    clouds.put("Special Clouds", "Mammatus");
    clouds.put("Special Clouds", "Lenticular");
    clouds.put("Special Clouds", "Fog");
    clouds.put("Special Clouds", "Contrails");

    String keysAndValuesJoined = Joiner
            .on(", ")
            .withKeyValueSeparator(" has type ")
            .join(clouds.entries());

    assertEquals("Cirrus has type Cirrus, "
            + "Cirrus has type Cirrostratus, "
            + "Cirrus has type Cirrocumulus, "
            + "Vertical Growth has type Cumulus, "
            + "Vertical Growth has type Cumulonimbus, "
            + "Alto has type Altostratus, "
            + "Alto has type Altocumulus, "
            + "Stratus has type Stratus, "
            + "Stratus has type Stratocumulus, "
            + "Stratus has type Nimbostratus, "
            + "Special Clouds has type Mammatus, "
            + "Special Clouds has type Lenticular, "
            + "Special Clouds has type Fog, "
            + "Special Clouds has type Contrails",
            keysAndValuesJoined);
}