Guava is a library developed by Google that includes common libraries useful for Java projects. It contains functionality for strings, collections, caching, parallel programming, primitives, and more. Some key features include immutable collections, functional idioms, caching, and an event bus. The goals of Guava are to be intuitive, encourage best practices, and avoid reinventing existing solutions.

1. Google Guava
by Yuriy Krutko
Java Developer

2. Common Myths
Guava is a fruit
Guavas (singular Guava, English pronunciation: /ˈgwɑː.və/[2]) are
plants in the Myrtle family (Myrtaceae) genus Psidium (meaning
"pomegranate" in Latin)
Guava is Google Collections
Guava misuses functional idioms

3. What's inside
Strings Ordering Throwables
Concurrency
Preconditions Collections
Reflection EventBus
Objects
Hashing Caches
I/O
Math
Primitives
Ranges

4. Why Guava?
• Guava is a productivity multiplier
• I Could've Invented That
• "Know and use the libraries”
• Don't reinvent the wheel.
• Could not be included into Java API

5. Guava Design Principles
• API is the best solution for use case.
• Obvious and intuitive outside. "Smart" inside.
• Encourage good code habits.
• Generic tools that can be composed.
• Emphasize maintainability.

6. equals, hashCode, toString
Code it yourself
Generate using tools (e.g. Eclipse)
Use Guava Objects class

7. Generated
private String firstName;
private String secondName;
@Override
public String toString() {
return "PersonGenerated [firstName=" + firstName
+ ", secondName=" + secondName + "]";
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result
+ ((firstName == null) ? 0 : firstName.hashCode());
result = prime * result
+ ((secondName == null) ? 0 : secondName.hashCode());
return result;
}

8. Generate
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
PersonGenerated other = (PersonGenerated) obj;
if (firstName == null) {
if (other.firstName != null)
return false;
} else if (!firstName.equals(other.firstName))
return false;
if (secondName == null) {
if (other.secondName != null)
return false;
} else if (!secondName.equals(other.secondName))
return false;
return true;
}

9. Objects
private String firstName;
private String secondName;
@Override
public int hashCode() {
return Objects.hashCode(firstName, secondName);
}
@Override
public boolean equals(Object obj) {
if (obj instanceof PersonGuava) {
PersonGuava other = (PersonGuava) obj;
return Objects.equal(firstName, other.firstName)
&& Objects.equal(secondName, other.secondName);
}
return false;
}
@Override
public String toString() {
return Objects.toStringHelper(this)
.add("firstName", firstName)
.add("secondName", secondName)
.toString();
}

10. Puzzler
Objects.hashCode(a) == a.hashCode() ?
Arrays.hashCode(new Object[] { a }) == a.hashCode() ?
public static int hashCode(Object a[]) {
if (a == null)
return 0;
int result = 1;
for (Object element : a)
result = 31 * result
+ (element == null ? 0 : element.hashCode());
return result;
}

11. Compare while equal
public class PairOfInts {
private int first;
private int second;
public static Comparator<PairOfInts> comparator() {
return new Comparator<PairOfInts>() {
@Override
public int compare(PairOfInts p1, PairOfInts p2) {
if (p1.first < p2.first) {
return -1;
}
if (p1.first == p2.first) {
if (p1.second < p2.second) {
return -1;
}
if (p1.second == p2.second) {
return 0;
}
}
return 1;
}
};
}
}

12. Compare while equal
public class PairOfInts {
private int first;
private int second;
comparatorInts() {
public static Comparator<PairOfInts> comparator() {
return new Comparator<PairOfInts>() {
@Override
public int compare(PairOfInts p1, PairOfInts p2) {
int res = Ints.compare(p1.first, p2.first);
if (p1.first < p2.first) {
if (res == 0) {
return -1;
} return Ints.compare(p1.second, p2.second);
}
if (p1.first == p2.first) {
return res;
if (p1.second < p2.second) {
} return -1;
}; }
} if (p1.second == p2.second) {
return 0;
}
}
return 1;
}
};
}
}

13. Compare while equal
public class PairOfInts {
private int first;
private int second;
public static Comparator<PairOfInts> comparator() {
Ordering<PairOfInts> ordering() {
comparatorInts() {
Ordering.from(new Comparator<PairOfInts>() {
return new Comparator<PairOfInts>() {
@Override
public int compare(PairOfInts p1, PairOfInts p2) {
return = Ints.compare(p1.first, p2.first);
int resInts.compare(p1.first, p2.first);
if (p1.first < p2.first) {
} if (res == 0) {
return -1;
}).compound(new Comparator<PairOfInts>() { p2.second);
} return Ints.compare(p1.second,
@Override
}
if (p1.first == p2.first) {
public int res;
return compare(PairOfInts p1, PairOfInts p2) {
if (p1.second < p2.second) {
} return Ints.compare(p1.second, p2.second);
return -1;
}; } }
} }); if (p1.second == p2.second) {
} return 0;
}
}
return 1;
}
};
}
}

14. Compare while equal
public class PairOfInts {
private int first;
private int second;
public static Comparator<PairOfInts> comparator() {
Ordering<PairOfInts> ordering() {
orderingLexicographical() {
comparatorInts() {
Ordering.<Comparable<?>> natural()
Ordering.from(new Comparator<PairOfInts>() {
return new Comparator<PairOfInts>() {
.lexicographical().onResultOf(
@Override
public int compare(PairOfIntsIterable<Comparable<?>>>() {
new Function<PairOfInts, p1, PairOfInts p2) {
return = Ints.compare(p1.first, p2.first);
int resInts.compare(p1.first, p2.first);
@Override
if (p1.first < p2.first) {
} if (res == 0) {
public Iterable<Comparable<?>> apply(PairOfInts pair) {
return -1;
}).compound(new Comparator<PairOfInts>() { p2.second);
} return Ints.compare(p1.second,
return ImmutableList.<Comparable<?>>
@Override
} of(pair.first, pair.second);
if (p1.first == p2.first) {
public int res;
return compare(PairOfInts p1, PairOfInts p2) {
}
if (p1.second < p2.second) {
} });
return Ints.compare(p1.second, p2.second);
return -1;
} }; } }
} }); if (p1.second == p2.second) {
} return 0;
}
}
return 1;
}
};
}
}

15. Compare while equal
public class PairOfInts {
private int first;
private int second;
public static Comparator<PairOfInts> comparator() {
Ordering<PairOfInts> ordering() {
orderingLexicographical() {
comparatorInts() {
Ordering.<Comparable<?>> natural()
Ordering.from(new Comparator<PairOfInts>() {
return new Comparator<PairOfInts>() {
.lexicographical().onResultOf(
@Override
public int compare(PairOfIntsIterable<Comparable<?>>>() {
new Function<PairOfInts, p1, PairOfInts p2) {
return = Ints.compare(p1.first, p2.first);
int resInts.compare(p1.first, p2.first);
@Override
if (p1.first < p2.first) {
} if (res == 0) {
public Iterable<Comparable<?>> apply(PairOfInts pair) {
return -1;
}).compound(new Comparator<PairOfInts>() { p2.second);
} return Ints.compare(p1.second,
return ImmutableList.<Comparable<?>>
@Override
} of(pair.first, pair.second);
if (p1.first == p2.first) {
public int res;
return compare(PairOfInts p1, PairOfInts p2) {
}
if (p1.second < p2.second) {
} });
return Ints.compare(p1.second, p2.second);
return -1;
} }; } }
} }); if (p1.second == p2.second) {
} return 0;
}
}
return 1;
}
};
}
}

16. Better Nulls
public class BetterNulls {
public static final String DEFAULT = "default";
public String neverNullDefault(String value) {
return Objects.firstNonNull(value, DEFAULT);
}
public String neverNullEmpty(String value) {
return Strings.nullToEmpty(value);
}
public String getValueByKey(String key, Map<String, String> map) {
return Functions.forMap(map, DEFAULT).apply(key);
}
public Optional<String> getValueByKeyOptional(String key, Map<String, String> map) {
if (map.containsKey(key)) {
return Optional.fromNullable(map.get(key));
}
return null;
}
}

17. Failfast and Join with Joy
public class PreconditionsJoiner {
public String joinStrings(Iterable<String> strings) {
Preconditions.checkNotNull(strings, "Strings should not be null");
return Joiner.on(", ").skipNulls().join(strings);
}
}

18. Measure everything
public void measureSomething() {
Stopwatch stopwatch = new Stopwatch();
for (int i = 0; i < COUNT; i++) {
stopwatch.start();
doSomething();
stopwatch.stop();
doUnimpotantThing();
stopwatch.start();
doOtherThing();
stopwatch.stop();
}
System.out.println("Average execution time "
+ stopwatch.elapsedTime(TimeUnit.NANOSECONDS) / COUNT + "ns");
}

19. Fast and Immutable
public List<Integer> createList(int[] elements) {
return ImmutableList.copyOf(Ints.asList(elements));
}
public Map<String, String> createMap() {
return ImmutableMap.of("key1", "val1", "key2", "val2");
}
public Map<String, String> buildMap() {
return ImmutableMap.<String, String> builder()
.put("key1", "val1")
.put("key2", "val2")
.build();
}

20. More collections
public void biMap() {
BiMap<Integer, String> biMap = HashBiMap.create();
BiMap<String, Integer> inverseBiMap = biMap.inverse();
}
public void multimap() {
Multimap<Integer, String> multiMap = ArrayListMultimap.create();
multiMap.put(10, "val1");
multiMap.put(10, "val2");
Collection<String> values = multiMap.get(10);
}
Table<Vertex, Vertex, Double> weightedGraph = HashBasedTable.create();
weightedGraph.put(v1, v2, 4.0);
weightedGraph.put(v1, v3, 20.0);
weightedGraph.put(v2, v3, 5.0);
Map<Vertex, Double> row = weightedGraph.row(v1);
Map<Vertex, Double> column = weightedGraph.column(v3);

21. Double checked locking
public class DCL {
private static final Supplier<Object> supplier = Suppliers
.memoize(new Supplier<Object>() {
@Override
public Object get() {
return loadResource();
}
});
private static Object loadResource() {
return new Object();
}
public static Object getResource() {
return supplier.get();
}
}

22. Memoize and Expire
public class DCLExp {
private static final Supplier<Object> supplier = Suppliers
.memoizeWithExpiration(new Supplier<Object>() {
@Override
public Object get() {
return loadResource();
}
}, 10, TimeUnit.MINUTES);
private static Object loadResource() {
return new Object();
}
public static Object getResource() {
return supplier.get();
}
}

23. Cache
public class CacheSample {
private final LoadingCache<String, Object> cache = CacheBuilder.newBuilder()
.maximumSize(1000)
.initialCapacity(100)
.concurrencyLevel(10)
.expireAfterAccess(30, TimeUnit.SECONDS)
.recordStats()
.build(new CacheLoader<String, Object>() {
@Override
public Object load(String key) throws Exception {
return loadResourceByKey(key);
}
});
private Object loadResourceByKey(String key) {
return new Object();
}
public Object getCachedValue(String key) {
return cache.getUnchecked(key);
}
public CacheStats getStats() {
return cache.stats();
}
}

24. Functional Idioms
public static Multiset<Integer> one(Iterable<String> strings) {
Function<String, Integer> lengthFunction = new Function<String, Integer>() {
@Override
public Integer apply(String string) {
return string.length();
}
};
Predicate<String> allCaps = new Predicate<String>() {
@Override
public boolean apply(String string) {
return CharMatcher.JAVA_UPPER_CASE.matchesAllOf(string);
}
};
return HashMultiset.create(Iterables.transform(
Iterables.filter(strings, allCaps), lengthFunction));
}

25. Functional Idioms
public static Multiset<Integer> two(Iterable<String> strings) {
return HashMultiset.create(
FluentIterable.from(strings)
.filter(new Predicate<String>() {
@Override
public boolean apply(String string) {
return CharMatcher.JAVA_UPPER_CASE
.matchesAllOf(string);
}
})
.transform(new Function<String, Integer>() {
@Override
public Integer apply(String string) {
return string.length();
}
}));
}

26. Functional Idioms
public static Multiset<Integer> one(Iterable<String> strings) { {
three(Iterable<String> strings)
Function<String, Integer> lengthFunction = new Function<String, Integer>() {
Multiset<Integer> lengths = HashMultiset.create();
for @Override
(String string : strings) {
public Integer apply(String string) {
if (CharMatcher.JAVA_UPPER_CASE.matchesAllOf(string)) {
return string.length();
lengths.add(string.length());
}
};
}
Predicate<String> allCaps = new Predicate<String>() {
return lengths;
} @Override
public boolean apply(String string) {
return CharMatcher.JAVA_UPPER_CASE.matchesAllOf(string);
}
};
return HashMultiset.create(Iterables.transform(
Iterables.filter(strings, allCaps), lengthFunction));
}

27. Catching a Bus
public class BaseEvent {
}
public class SpecificEvent extends BaseEvent {
}
public class OtherSpecificEvent extends BaseEvent {
}
public interface EventListener {
void handleSpecific(SpecificEvent event);
void handleOtherSpecific(OtherSpecificEvent event);
}
public class EventListenerAdapter implements EventListener {
@Override
public void handleSpecific(SpecificEvent event) {
}
@Override
public void handleOtherSpecific(OtherSpecificEvent event) {
}
}

28. Catching a Bus
public class EventDispatcher {
private List<EventListener> listeners = new CopyOnWriteArrayList<EventListener>();
public void addListener(EventListener listener) {
listeners.add(listener);
}
public void removeListener(EventListener listener) {
listeners.add(listener);
}
public void fireSpecific(SpecificEvent event) {
for (EventListener listener : listeners) {
listener.handleSpecific(event);
}
}
public void fireOtherSpecific(OtherSpecificEvent event) {
for (EventListener listener : listeners) {
listener.handleOtherSpecific(event);
}
}
}

29. Event Bus
public class BaseEvent {
}
public class SpecificEvent extends BaseEvent {
}
public class OtherSpecificEvent extends BaseEvent {
}

30. Event Bus
public class EBExample {
private static final EventBus eventBus = new EventBus();
public static void main(String[] args) {
eventBus.register(new Object() {
@Subscribe
public void handle(SpecificEvent event) {
System.out.println("SpecificEvent: " + event.getClass());
}
});
eventBus.register(new Object() {
@Subscribe
@AllowConcurrentEvents
public void handle(BaseEvent event) {
System.out.println("BaseEvent: " + event.getClass());
}
});
eventBus.post(new SpecificEvent());
}
}

31. Even more...
• IO
• Net
• Reflect
• Throwables
• Hashing
• Math
• CaseFormat
• Concurrency

32. Apache Commons
• Just another library
• Commons > Guava (BCEL, Fvs, Email)
• Guava is more consistent
• Guava uses generics
• Guava Commons != {}
• Guava doesn't solve global tasks
• Don't shoot yourself in the foot with
Guava

33. Thank you !
● Yuriy Krutko (yuri.krutko@odnoklassniki.ru)
● Guava (http://code.google.com/p/guava-libraries/)