Guava - Elements of Functional Programming

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GUAVA
Elements of Functional Programming
By Andriy Slobodyanyk

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Map Function
[2, 3, 5]
y = x * x
[4, 9, 25]

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Groovy
[2,3,5].collect {it * it}; // [4,9,25]
[50, 100, 200].find {it >= 100}; // 100
team.any {Member m -> m.gender == FEMALE};// true
["Ann", "Alex", "Andrey"].every {it.startsWith("A")};
//true
[3, 7, 10].max(); // 10

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ServiceImpl
public List<Dto> getAllRecords() {
List<Dto> result = new ArrayList<>();
for (Entity entity : repository.getEntities()) {
Dto dto = new Dto();
dto.setField(entity.getField());
result.add(dto);
}
return result;
}

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ServiceImpl
public Dto getRecordByText(String text) {
Entity entity = repository.getEntityByText(text);
Dto dto = new Dto();
dto.setField(entity.getField());
return dto;
}

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Function Interface
public interface Function<F, T> {
T apply(F input);
}

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EntityToDtoFunc
public class EntityToDtoFunc implements Function<Entity, Dto> {
public Dto apply(Entity entity) {
Dto dto = new Dto();
dto.setField(entity.getField());
return dto;
}
}

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ServiceImpl
public List<Dto> getAllRecords() {
return Lists.transform(
repository.getEntities(), new EntityToDtoFunc());
}
public Dto getRecordByText(String text) {
Entity entity = repository.getEntityByText(text);
return new EntityToDtoFunc().apply(entity);
}

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Predicate
public List<Person> getVips (List<Person> source) {
List<Person> result = new ArrayList<>();
for (Person p : source) {
if (p.getGender() == FEMALE || p.getAge() <= 16) {
result.add(p);
}
}
return result;
}

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Predicate
public interface Predicate<T> {
boolean apply(T input);
}

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Vip Person Predicate
public enum VipPersonPredicate implements Predicate<Person> {
INSTANCE;
@Override
public boolean apply(Person p) {
return p.getGender() == FEMALE || p.getAge() <= 16;
}
}

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Predicate
public List<Person> getVips (List<Person> source) {
return Iterables.filter(
source, VipPersonPredicate.INSTANCE);
}

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FluentIterable
FluentIterable
.from(database.getClientList())
.filter(activeInLastMonth())
.transform(Functions.toStringFunction())
.limit(10)
.toList();

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FluentIterable
public List<Dto> getAllRecords() {
return FluentIterable
.from(repository.getEntities())
.transform(EntityToDtoFunc.INSTANCE)
.toList();
}
public List<Person> getVips (List<Person> source) {
return FluentIterable
.from(source)
.filter(VipPersonPredicate.INSTANCE)
.toList();
}

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Optional
List<Dto> records = service.getAllRecords();
for (Dto dto : records) {
// some action
}

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Optional
Person person = service.findRecordBy(text);
person.getName(); // NPE???

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Optional
Person person = service.findRecordBy(text);
if (person != null ) {
person.getName();
}

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Optional
 null
 exception
 new Person()
 NO_PERSON
 Optional

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Optional
Optional<Integer> possible = Optional.of(5);
possible.isPresent(); // returns true
possible.get(); // returns 5

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Optional
Optional<Person> optPerson = service.findRecordBy(text);
if (optPerson.isPresent()) {
Person person = optPerson.get();
person.getName();
}

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Optional
Optional<Person> optPerson = service.findRecordBy(text);
optPerson.or(DEFAULT_PERSON);
optPerson.orNull();
optPerson.asSet();

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Optional
Optional<Person> optPerson = service.findRecordBy(text);
for (Person p : optPerson.asSet()) {
person.getName();
}

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Cache
public class ServiceImpl {
public Foo findFooByStr(String str) {
// long term running code
return result;
}
}

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Cache
public class ServiceImpl {
public Foo findFooByStr(key) {
fooCache.get(str);
}
private LoadingCache<Key, Graph> fooCache = CacheBuilder.newBuilder()
.maximumSize(1000)
.expireAfterWrite(10, TimeUnit.MINUTES)
.build(
new CacheLoader<String, Foo>() {
public Foo load(String str) throws AnyException {
// long term running code
return result;

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Joiner
String title;
String firstName;
String lastName;
// Mr. Vasiliy Pupkin
return title + + firstName + + lastName;

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Joiner
public String getFullName() {
return Joiner.on(“ “)
.skipNulls()
.join(title, firstName, lastName);
}

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Guava
 Optinal
 FluentIterable
 Cache
 Joiner
 Collections
 EventBus
 Ordering
 Preconditions

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