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Commit 69168df

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update exercise solutions using new features in Java 10-17
1 parent f7f671e commit 69168df

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4 files changed

+26
-34
lines changed

4 files changed

+26
-34
lines changed

‎src/com/example/exercises/Exercise10.java

Lines changed: 6 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -1,13 +1,9 @@
11
package com.example.exercises;
22

3-
import static java.lang.String.format;
4-
import static java.lang.System.out;
53
import static java.util.Comparator.comparing;
6-
import static java.util.function.BinaryOperator.maxBy;
74
import static java.util.stream.Collectors.groupingBy;
8-
import static java.util.stream.Collectors.reducing;
5+
import static java.util.stream.Collectors.maxBy;
96

10-
import java.util.Map;
117
import java.util.Optional;
128
import java.util.function.BiConsumer;
139

@@ -22,19 +18,13 @@
2218
*/
2319
public class Exercise10 {
2420
private static final WorldDao worldDao = InMemoryWorldDao.getInstance();
25-
26-
private static final BiConsumer<String,Optional<Country>> printEntry =
27-
(continent,country) -> out.println(format("%s: %s",continent,country.get()));
28-
21+
private static final BiConsumer<String,Optional<Country>> printEntry = (continent,country) -> System.out.printf("%s: %s\n",continent,country.get());
2922
public static void main(String[] args) {
3023
// Find the richest country of each continent with respect to their GNP (Gross National Product) values.
31-
final Map<String, Optional<Country>> richestCountryByContinent =
32-
worldDao.findAllCountries()
33-
.stream()
34-
.collect(
35-
groupingBy(Country::getContinent,
36-
reducing(maxBy(comparing(Country::getGnp))))
37-
);
24+
var richestCountryByContinent =
25+
worldDao.findAllCountries()
26+
.stream()
27+
.collect(groupingBy(Country::getContinent,maxBy(comparing(Country::getGnp))));
3828
richestCountryByContinent.forEach(printEntry);
3929
}
4030

‎src/com/example/exercises/Exercise11.java

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2,8 +2,6 @@
22

33
import static java.util.stream.Collectors.summarizingLong;
44

5-
import java.util.LongSummaryStatistics;
6-
75
import com.example.dao.InMemoryWorldDao;
86
import com.example.dao.WorldDao;
97
import com.example.domain.Country;
@@ -18,7 +16,9 @@ public class Exercise11 {
1816

1917
public static void main(String[] args) {
2018
// Find the minimum, the maximum and the average population of world countries
21-
final LongSummaryStatistics populationSummary = worldDao.findAllCountries().stream()
19+
var populationSummary =
20+
worldDao.findAllCountries()
21+
.stream()
2222
.collect(summarizingLong(Country::getPopulation));
2323
System.out.println(populationSummary);
2424
}

‎src/com/example/exercises/Exercise12.java

Lines changed: 5 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1,11 +1,9 @@
11
package com.example.exercises;
22

3-
import static java.lang.System.out;
43
import static java.util.stream.Collectors.groupingBy;
54
import static java.util.stream.Collectors.summarizingLong;
65

76
import java.util.LongSummaryStatistics;
8-
import java.util.Map;
97
import java.util.function.BiConsumer;
108

119
import com.example.dao.InMemoryWorldDao;
@@ -20,13 +18,14 @@
2018
public class Exercise12 {
2119
private static final WorldDao worldDao = InMemoryWorldDao.getInstance();
2220

23-
private static final BiConsumer<String, LongSummaryStatistics> printEntry = (continent, statistics) -> out
24-
.println(String.format("%s: %s", continent, statistics));
21+
private static final BiConsumer<String, LongSummaryStatistics> printEntry = (continent, statistics) -> System.out.printf("%s: %s\n", continent, statistics);
2522

2623
public static void main(String[] args) {
2724
// Find the minimum, the maximum and the average population of each continent.
28-
final Map<String, LongSummaryStatistics> populationSummaryByContinent = worldDao.findAllCountries().stream()
29-
.collect(groupingBy(Country::getContinent, summarizingLong(Country::getPopulation)));
25+
var populationSummaryByContinent =
26+
worldDao.findAllCountries()
27+
.stream()
28+
.collect(groupingBy(Country::getContinent, summarizingLong(Country::getPopulation)));
3029
populationSummaryByContinent.forEach(printEntry);
3130
}
3231

Lines changed: 12 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -1,15 +1,15 @@
11
package com.example.exercises;
22

3-
import com.example.dao.InMemoryWorldDao;
4-
import com.example.dao.WorldDao;
5-
import com.example.domain.Country;
3+
import static java.lang.System.out;
4+
import static java.util.Comparator.comparingDouble;
65

76
import java.util.Collection;
87
import java.util.Comparator;
98
import java.util.function.Predicate;
109

11-
import static java.lang.System.out;
12-
import static java.util.Comparator.comparingDouble;
10+
import com.example.dao.InMemoryWorldDao;
11+
import com.example.dao.WorldDao;
12+
import com.example.domain.Country;
1313

1414
/**
1515
*
@@ -21,14 +21,17 @@ public class Exercise9 {
2121

2222
private static final Comparator<Country> populationDensityComparator = comparingDouble(country -> country.getPopulation() / country.getSurfaceArea());
2323
private static final Predicate<Country> livesNobody = country -> country.getPopulation() == 0L;
24-
24+
2525
public static void main(String[] args) {
26-
// Sort the countries by their population densities in descending order ignoring zero population countries
27-
Collection<Country> countries = worldDao.findAllCountries();
26+
// Sort the countries by their population densities in descending order ignoring
27+
// zero population countries
28+
var countries = worldDao.findAllCountries();
29+
var countriesSortedByPopulationDensityDescOrder =
2830
countries.stream()
2931
.filter(livesNobody.negate())
3032
.sorted(populationDensityComparator.reversed())
31-
.forEach(out::println);
33+
.toList();
34+
countriesSortedByPopulationDensityDescOrder.forEach(out::println);
3235
}
3336

3437
}

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