Maps utility example

There are various places around leveluplunch that show the power of guava's Maps utility class such as convert list to map, convert properties to map, filter map by entries, filter map by values, filter map by keys and initialize map. This example will try to bring it together in one page.

Setup

private static final Logger logger = Logger.getLogger(ConvertCollectionToArray.class);

class State {
    
    String code;
    String name;
    String region;
    double population;

    public State(String code, String name, String region, double population) {
        super();
        this.code = code;
        this.name = name;
        this.region = region;
        this.population = population;
    }        
    
    @Override
    public String toString() {
        return com.google.common.base.Objects.toStringHelper(this)
                .add("code", code).add("name", name)
                .toString();
    }
    
}

List<State> states;

/**
 * Seed data
 */
@Before
public void setUp () {
    
    states = Lists.newArrayList();
    
    states.add(new State("WI", "Wisconsin", "MDW", 5726398));
    states.add(new State("FL", "Florida", "SE", 19317568));
    states.add(new State("IA", "Iowa", "MDW", 3078186));
    states.add(new State("CA", "California", "W", 38041430));
    states.add(new State("NY", "New York", "NE", 19570261));
    states.add(new State("CO", "Colorado", "W", 5187582));
    states.add(new State("OH", "Ohio", "MDW", 11544225));
    states.add(new State("ME", "Maine", "NE", 1329192));
    states.add(new State("SD", "South Dakota", "MDW", 833354));
    states.add(new State("TN", "Tennessee", "SE", 6456243));
    states.add(new State("OR", "Oregon", "W", 3899353));
}

Initialize map

@Test
public void intialize_map () {
    
    Map<String, String> newMap = Maps.newHashMap();
    
    assertNotNull(newMap);
}

Convert list to map

@Test
public void maps_unique_index() {

    Map<String, State> statesKeyByCode = Maps.uniqueIndex(states,
            new Function<State, String>() {
                public String apply(State from) {
                    return from.code;
                }
            });

    logger.info(statesKeyByCode);

    assertThat(statesKeyByCode, hasKey("WI"));
}

Output

{
    WI=STATE{CODE=WI, NAME=WISCONSIN}, 
    FL=STATE{CODE=FL, NAME=FLORIDA}, 
    IA=STATE{CODE=IA, NAME=IOWA}, 
    CA=STATE{CODE=CA, NAME=CALIFORNIA}, 
    NY=STATE{CODE=NY, NAME=NEW YORK}, 
    CO=STATE{CODE=CO, NAME=COLORADO}, 
    OH=STATE{CODE=OH, NAME=OHIO}, 
    ME=STATE{CODE=ME, NAME=MAINE}, 
    SD=STATE{CODE=SD, NAME=SOUTH DAKOTA}, 
    TN=STATE{CODE=TN, NAME=TENNESSEE}, 
    OR=STATE{CODE=OR, NAME=OREGON}
}

Convert properties to map

@Test
public void map_of_properties() {

    Properties properties = new Properties();
    properties.put("leveluplunch.java.examples",
            "http://www.leveluplunch.com/java/examples/");
    properties.put("leveluplunch.java.exercises",
            "http://www.leveluplunch.com/java/exercises/");
    properties.put("leveluplunch.java.tutorials",
            "http://www.leveluplunch.com/java/tutorials/");

    Map<String, String> mapOfProperties = Maps.fromProperties(properties);

    logger.info(mapOfProperties);

    assertThat(mapOfProperties, hasKey("leveluplunch.java.examples"));

}

Output

{
    leveluplunch.java.exercises=http://www.leveluplunch.com/java/exercises/, 
    leveluplunch.java.examples=http://www.leveluplunch.com/java/examples/, 
    leveluplunch.java.tutorials=http://www.leveluplunch.com/java/tutorials/
}

Filter map by entries

public void maps_filter_entries() {

    // create a map
    Map<String, State> statesKeyByCode = Maps.uniqueIndex(states,
            new Function<State, String>() {
                public String apply(State from) {
                    return from.code;
                }
            });

    // predicate to filter states by region code
    Predicate<Entry<String, State>> byMDWStates = new Predicate<Map.Entry<String, State>>() {
        @Override
        public boolean apply(Entry<String, State> input) {
            return input.getValue().region.equals("MDW");
        }
    };

    // filter entries
    Map<String, State> midwestStates = Maps.filterEntries(statesKeyByCode,
            byMDWStates);

    logger.info(midwestStates);

    assertThat(midwestStates.keySet(), hasSize(5));
}

Output

{
    WI=State{code=WI, name=Wisconsin}, 
    IA=State{code=IA, name=Iowa}, 
    OH=State{code=OH, name=Ohio}, 
    SD=State{code=SD, name=South Dakota}
}

Filter map by keys

public void map_filter_keys() {

    // create a map
    Map<String, State> statesKeyByCode = Maps.uniqueIndex(states,
            new Function<State, String>() {
                public String apply(State from) {
                    return from.code;
                }
            });

    Predicate<String> byStateCodeContainsVowelI = new Predicate<String>() {
        @Override
        public boolean apply(String stateCode) {
            return stateCode.contains("I");
        }
    };

    Map<String, State> stateCodeWithVowelI = Maps.filterKeys(
            statesKeyByCode, byStateCodeContainsVowelI);

    logger.info(stateCodeWithVowelI);

    assertThat(stateCodeWithVowelI.keySet(), hasSize(2));
}

Output

{
    WI=State{code=WI, name=Wisconsin}, 
    IA=State{code=IA, name=Iowa}
}

Filter map by values

@Test
public void map_filter_by_values() {

    // create a map
    Map<String, State> statesKeyByCode = Maps.uniqueIndex(states,
            new Function<State, String>() {
                public String apply(State from) {
                    return from.code;
                }
            });

    Predicate<State> by15MillionOrGreater = new Predicate<State>() {
        @Override
        public boolean apply(State input) {
            return input.population >= 15000000;
        }
    };

    Map<String, State> populationGT15Million = Maps.filterValues(
            statesKeyByCode, by15MillionOrGreater);

    logger.info(populationGT15Million);

    assertThat(populationGT15Million.keySet(), hasSize(3));
}

Output

{
    FL=State{code=FL, name=Florida}, 
    CA=State{code=CA, name=California}, 
    NY=State{code=NY, name=New York}
}