Google Guava is a set of core Java libraries that includes collections, caching, predicates and functions, primitives support, and other utilities. It aims to fill in gaps in the Java class library and improve on Java SE classes. Some key features include optional types, immutable collections, caching utilities, character matching, and functional interfaces like predicates and functions. Guava provides utilities to avoid null checks, filter collections, transform values, and load resources. It also includes hashing, bloom filters, and other utilities. Using Guava can make code cleaner and safer by leveraging well-tested utilities rather than reimplementing functionality.

1. @mitemitreski
The core libraries you
always wanted
Google Guava

3. What is Google Guava?
com.google.common.annotation
com.google.common.base
com.google.common.collect
com.google.common.io
com.google.common.net
com.google.common.primitives
com.google.common.util.concurrent
...

4. Code in slides

5. Apache 2 license
latest release is 18.0,
released August 25, 2014.
Guava facts

6. NULL it is
"Null sucks." - Doug Lea
"I call it my billion-dollar
mistake." - C. A. R. Hoare

7. Null is ambiguous
if ( x != null && x.someM()!=null && ) {
// work with x.someM()
}
Boolean isAwesome ; // can be NULL, TRUE, FALSE
Assert.notNull(x);
Assert.notNull(x.someM());
// work with x.someM()

8. import com.google.common.base.*
@Test
public void optionalExample() {
Optional<Integer> possible = Optional.of(3); // Make optional of given type
possible.isPresent(); // evaluate to true if nonNull
possible.or(10); // evaluate to possible's value or default
possible.get(); // evaluate to 3
}

9. import com.google.common.base.*
public void testNeverNullWithoutGuava() {
Integer defaultId = null;
Integer id = theUnknowMan.getId() != null ? theUnknowMan.getId() : defaultId;
assertNotNull(id);
}
public void firstNotNull() {
Integer a = Objects.firstNonNull(null, 3); // will evaluate to 3
Integer b = Objects.firstNonNull(9, 3); // //will evaluate to 9
assertEquals(Integer.valueOf(3), a);
assertEquals(Integer.valueOf(9), b);
}

10. import static com.google.common.base.Preconditions.*;
private Customer theUnknowMan = new Customer();
@Test(expected = IllegalArgumentException.class)
public void somePreconditions() {
checkNotNull(theUnknowMan.getId()); // Will throw NPE
checkState(!theUnknowMan.isSick()); // Will throw IllegalStateException
checkArgument(theUnknowMan.getAddress() != null,
"We couldn't find the description for customer with id %s", theUnknowMan.
getId());
}

11. JSR-305 Annotations for software defect detection
@Nullable @NotNull
1. javax.validation.constraints.NotNull - EE6
2. edu.umd.cs.findbugs.annotations.NonNull – Findbugs, Sonar
3. javax.annotation.Nonnull – JSR-305
4. com.intellij.annotations.NotNull - IntelliJIDEA
The Executive Committee voted to list this JSR as dormant in May 2012.

12. But JDK 8 has java.util.Optional
… and java.util.Objects
… and guava has com.google.common.base.MoreObjects

13. import static com.google.common.base.Preconditions.*;
private Customer theUnknowMan = new Customer();
@Test(expected = IllegalArgumentException.class)
public void somePreconditions() {
checkNotNull(theUnknowMan.getId()); // Will throw NPE
checkState(!theUnknowMan.isSick()); // Will throw IllegalStateException
checkArgument(theUnknowMan.getAddress() != null,
"We couldn't find the description for customer with id %s", theUnknowMan.
getId());
}
JDK8+ just use java.util.
Objects + Optional

14. API Deprecation

15. @Beta annotated API is subject to change any
time
@Deprecated annotated API is removed
in 18+ months after depreciation
Serialization compatibility is NOT
guaranteed

16. Guava's "fluent" Comparator class.
Ordering<Customer> ordering = Ordering
.natural()
.nullsFirst().onResultOf(
new Function<Customer, Comparable>() {
@Override
public Comparable apply(Customer customer) {
return customer.getName();
}
}
);

17. Wrapper overload

18. Character Matchers
Use a predefined constant (examples)
• CharMatcher.WHITESPACE (tracks Unicode defn.)
• CharMatcher.JAVA_DIGIT
• CharMatcher.ASCII
• CharMatcher.ANY
Use a factory method (examples)
• CharMatcher.is('x')
• CharMatcher.isNot('_')
• CharMatcher.oneOf("aeiou").negate()
• CharMatcher.inRange('a', 'z').or(inRange('A','Z'))

19. Character Matchers
String noControl = CharMatcher.JAVA_ISO_CONTROL.removeFrom(string);
String theDigits = CharMatcher.DIGIT.retainFrom(string);
String lowerAndDigit = CharMatcher.or(CharMatcher.JAVA_DIGIT,
CharMatcher.JAVA_LOWER_CASE).retainFrom(string);

20. import com.google.common.cache.*;
Cache<Integer, Customer> cache =
CacheBuilder.newBuilder()
.maximumSize(10000)
.build();

21. Eviction
Cache<Integer, Customer> cache =
CacheBuilder.newBuilder()
.expireAfterWrite(2, TimeUnit.MINUTES)
.build();
Cache<Integer, Customer> cache =
CacheBuilder.newBuilder()
.expireAfterAccess(2,TimeUnit.MINUTES)
.build();

22. Eviction
Cache<Integer, Customer> cache =
CacheBuilder.newBuilder()
.weigher(new Weigher<Integer, Customer>() {
@Override
public int weigh(Integer key, Customer value) {
return value.getName().length();
}
}).maximumWeight(20)
//0 all good 21 evict something
.build();

23. import com.google.common.cache.*;
Cache<Integer, Customer> cache =
CacheBuilder.newBuilder()
.weakKeys()
.maximumSize(10000)
.expireAfterWrite(10, TimeUnit.MINUTES)
.build();

24. It’s all about the numbers
Cache<Integer, Customer> cache =
CacheBuilder.newBuilder()
.recordStats()
.build();
CacheStats stats = cache.stats();
stats.hitRate();
stats.averageLoadPenalty();
stats.missCount();
stats.missRate();

25. Map != Cache
● Map.get causes a type-safety hole
● Map.get is a read operation and users don't
expect it to also write
● Map.equals is not symmetric on a self-populating
Map

26. com.google.common.collect.*;
• Immutable Collections
• Multimaps, Multisets, BiMaps... aka Google-
Collections
• Comparator-related utilities
• Stuff similar to Apache commons collections
• Some functional programming support
(filter/transform/etc.)

27. MultiMap

28. BiMap
● BiMap<K, V> is Map<K,V> with unique values
● Operations: all Map, inverse(), values() as Set
● Throws an IllegalArgumentException if you attempt to
map a key to an already-present value

29. Functions and Predicates
Function<String, Integer> lengthFunction = new Function<String, Integer>() {
public Integer apply(String string) {
return string.length();
}
};
Predicate<String> allCaps = new Predicate<String>() {
public boolean apply(String string) {
return CharMatcher.JAVA_UPPER_CASE.matchesAllOf(string);
}
};

30. Functions and Predicates
Function<String, Integer> lengthFunction = String::length;
Predicate<String> allCaps = CharMatcher.JAVA_UPPER_CASE::matchesAllOf;

31. Functional aka Single Abstract Method
interfaces - SAM

32. Functionality Guava JDK 8
Predicate apply(T input) test(T input)
Combining predicates Predicates.and/or/not Predicate.and/or/negate
Supplier Suplier.get Supplier.get
Joiner/StringJoiner Joiner.join() StringJoiner.add()
SettableFuture/CompletableFutu
re
SettableFuture.set(T input) CompletableFuture.complete(T input)
Optional Optional.of/ofNullable/empty Optional.of/fromNullable/absent

33. Filter collections
SortedMap<String, String> map = new TreeMap<>();
map.put("1", "one");
map.put("2", "two");
map.put("3", null);
map.put("4", "four");
SortedMap<String, String> filtered =
Maps.filterValues(map, Predicates.notNull());
assertThat(filtered.size(), is(3)); // null entry for "3" is gone!

34. Filter collections

35. Transform collections

36. Java 8 - aggregate operations
http://docs.oracle.com/javase/tutorial/collections/streams/index.html
roster
.stream()
.filter(e -> e.getGender() == Person.Sex.MALE)
.forEach(e -> System.out.println(e.getName());

37. Java 8 - aggregate operations
http://docs.oracle.com/javase/tutorial/collections/streams/index.html
double average = roster
.stream()
.filter(p -> p.getGender() == Person.Sex.MALE)
.mapToInt(Person::getAge)
.average()
.getAsDouble();

38. Collection goodies
// oldway
Map<String, Map<Long, List<String>>> mapOld = new
HashMap<String, Map<Long, List<String>>>();
// the guava way
Map<String, Map<Long, List<String>>> map = Maps.newHashMap();
// list
ImmutableList<String> of = ImmutableList.of("a", "b", "c");
// Same one for map
ImmutableMap<String, String> theMap = ImmutableMap.of("key1",
"value1", "key2", "value2");
//list of ints
List<Integer> theList = Ints.asList(1, 2, 3, 4, 522, 5, 6);

39. Load resources
Resources.getResource("com/tfnico/examples/guava/BaseTest.class");
// instead of this:
String location = "com/tfnico/examples/guava/BaseTest.class";
URL resource2 = this.getClass().getClassLoader().getResource(location);
Preconditions.checkArgument(resource2 != null, "resource %s not found",
location);

40. Hashing
HashFunction hf = Hashing.md5();
Customer c = new Customer();
// into is a primitive sink
Funnel<? super Customer> customerFunnel = (from, into) -> {
into.putString(from.getName(),Charsets.UTF_8);
into.putInt(from.getId());
};
HashCode hc = hf.newHasher()
.putLong(2)
.putString("Mite", Charsets.UTF_8)
.putObject(c, customerFunnel)
.hash();

41. Bloom filter
BloomFilter<Customer> awesomeCusumers =
BloomFilter.create(customerFunnel, 500, 0.01);
List<Customer> friendsList = Lists.newArrayList(
new Customer(),
new Customer());
for(Customer friend : friendsList) {
awesomeCusumers.put(friend);
}
Customer thatStrangeGuy = new Customer();
if (awesomeCusumers.mightContain(thatStrangeGuy)) {
//that strange guy is not a cusumer and we have reachet this line
//probablility 0.01
}

42. Bloom filter

43. When to use Guava?
● Temporary collections
● Mutable collections
● String Utils
● Check if (x==null)
● Always ?

44. Why use a Guava?
"I could just write that myself."
But… These things are much easier to mess up than it
seems
•With a library, other people will make your code faster and better
for You

45. Major stuff I did not mentioned
EventBus
IO
Reflection
Math
Ranges

47. BG-JUG and JugMK community