The document discusses the use of the Guava library in Java for various programming tasks, such as handling null values, implementing preconditions, and object comparison. It provides code examples illustrating features like collections management, input/output operations, and utility functions for string processing and caching. Guava enhances code quality by encouraging practices such as avoiding repetition and providing well-defined interfaces.

1. Facilite a vida com Guava
@programadorfsa
+RomualdoCosta
www.programadorfeirense.com.br

2. Problema: validação
boolean estaPreenchida = minhaString != null && minhaString.isEmpty();

3. Problema: ler um arquivo
try(BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {
StringBuilder sb = new StringBuilder();
String line = br.readLine();
while (line != null) {
sb.append(line);
sb.append(System.lineSeparator());
line = br.readLine();
}
String everything = sb.toString();
}

4. Software baseado em componentes
● Don’t repeat youself!
● Faça você mesmo ou pegue pronto.
● Interface bem definida e sem estado.
● Pode ser substituído por outro
componentes

5. Guava
● https://github.com/google/guava
● Java 1.6 ou maior
● Usadas em projetos Java do Google
● collections, caching, primitives support, concurrency libraries, common
annotations, string processing, I/O ...

6. Maven
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>19.0</version>
</dependency>

7. Gradle
dependencies {
compile 'com.google.guava:guava:19.0'
}

8. Lidando com valores nulos
Integer a=5;
Integer b=null;
//algumas operações
Optional<Integer> possible=Optional.fromNullable(a);
System.out.println(possible.isPresent());//tem algo não nulo?
System.out.println(possible.or(10));//se for nulo, retorna 10 por padrão
System.out.println(MoreObjects.firstNonNull(a, b));//seleciona entre dois
valores
String nome=new String();
System.out.println(Strings.isNullOrEmpty(nome));

9. Pré condições
import static com.google.common.base.Preconditions.checkElementIndex;
Integer[]arr=new Integer[5];
//algum código
int index=5;
checkElementIndex(index, arr.length, "index");
/*
Exception in thread "main" java.lang.IndexOutOfBoundsException: index (5) must be
less than size (5)
at com.google.common.base.Preconditions.checkElementIndex(Preconditions.java:
310)
at br.gdg.fsa.Main.main(Main.java:43)
*/

10. Pré condições
import static com.google.common.base.Preconditions.checkNotNull;
Integer a=null;
checkNull(a);
/*
Exception in thread "main" java.lang.NullPointerException
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:212)
at br.gdg.fsa.Main.main(Main.java:45)
*/

11. Pré condições
import static com.google.common.base.Preconditions.checkArgument;
int i=-1;
checkArgument(index >= 0, "Argument was %s but expected nonnegative", index);
/*
Exception in thread "main" java.lang.IllegalArgumentException: Argument was -1 but
expected nonnegative
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:146)
at br.gdg.fsa.Main.main(Main.java:46)
*/

12. Comparação de objetos
class Person implements Comparable<Person> {
public String lastName;
public String firstName;
public int zipCode;
public int compareTo(Person other) {
int cmp = lastName.compareTo(other.lastName);
if (cmp != 0) {
return cmp;
}
cmp = firstName.compareTo(other.firstName);
if (cmp != 0) {
return cmp;
}
return Integer.compare(zipCode, other.zipCode);
}
}

13. Comparação de objetos com Guava
class Person implements Comparable<Person> {
public String lastName;
public String firstName;
public int zipCode;
public int compareTo(Person that) {
return ComparisonChain.start()
.compare(this.lastName, that.lastName)
.compare(this.firstName, that.firstName)
.compare(this.zipCode, that.zipCode)
.result();
}
}

14. Ordenação
Integer[]arr=new Integer[5]; arr[0]=1; arr[1]=10; arr[2]=100; arr[3]
=1000; arr[4]=10000;
List<Integer> list = Lists.newArrayList(arr);
Ordering<Integer> ordering=Ordering.natural().reverse();
System.out.println(ordering.min(list)); //10000

15. Collections
Set<Type> copySet = Sets.newHashSet(elements);
List<String> theseElements = Lists.newArrayList("alpha", "beta",
"gamma");
List<Type> exactly100 = Lists.newArrayListWithCapacity(100);
List<Type> approx100 = Lists.newArrayListWithExpectedSize
(100);
Set<Type> approx100Set = Sets.newHashSetWithExpectedSize
(100);

16. Hashing
HashFunction hf = Hashing.md5();// seleciona algoritmo
HashCode hc = hf.newHasher()
.putLong(id)
.putString(name, Charsets.UTF_8)
.putObject(person, personFunnel)
.hash();
Funnel<Person> personFunnel = new Funnel<Person>() {
@Override
public void funnel(Person person, PrimitiveSink into) {
into
.putString(person.firstName, Charsets.UTF_8)
.putString(person.lastName, Charsets.UTF_8)
.putInt(person.zipcode);
}
};

17. IO
List<String> linhas = Files.readLines(arquivo, Charsets.UTF_8);
Closer closer = Closer.create();
try {
InputStream in = closer.register(openInputStream());
OutputStream out = closer.register(openOutputStream());
// do stuff with in and out
} catch (Throwable e) { // must catch Throwable
throw closer.rethrow(e);
} finally {
closer.close();
}

18. Ranges

19. Ranges
Range<Integer> range=Range.closed(1, 10);
ContiguousSet<Integer> values=ContiguousSet.create(range, DiscreteDomain.
integers());
List<Integer> list = Lists.newArrayList(values);

20. E muito mais...
● Imuttable Collections
● Novos Collections: BiMap, MultiMap, Table, RangeSet...
● EventBus
● Math
● Strings (split, join, match, charset)
● Caches
● Reflection
● Functional Idioms (Functions, Predicates)
● Primitives

21. Perguntas?