1. Guava
By Franck Benault
Created 01/07/2014
Last updated 02/08/2014

2. Guava plan
● Goal of Guava
● Limitations
● Reasons to use Guava ?
● Example

3. Goal of Guava
● Guava is low level core libraries coming from Google
project (Java6+)
● We should expect them in the JDK (JDK+)
● With Guava, the code looks good
– Less code
– Simplier code
– Cleaner code
– More readable code

4. Goal of Guava : quiz question
Quiz1
" foo, ,bar, quux,".split(",");
a [" foo"," ", "bar", " quux"]
b ["foo", "bar", "quux"]
c ["foo","", "bar", "quux"]
d [" foo"," ", "bar", " quux",""]

5. Goal of Guava : quiz answer
" foo, ,bar, quux,".split(",");
a [" foo"," ", "bar", " quux"]
b ["foo", "bar", "quux"] //probably what we want
c ["foo","", "bar", "quux"]
d [" foo"," ", "bar", " quux",""]

6. Goal of Guava : first example
● Splitter.on(',')
– .trimResults()
– .omitEmptyStrings()
– .split(" foo, ,bar, quux,");
● => ["foo", "bar", "quux"]

7. Goal of Guava : first application
● List<String> list = Lists.newArrayList(null, "two",
null, "four") ;
● Joiner.on(":")
– .userForNull("")
– .join(list);
● => ":two::four"

8. Limitation : Security fix breaks
Guava
● 22 janvier 2014, security fix in Java update51 breaks
Guava library
● Sun.reflect.generics.reflectiveObjects.TypeVariableImpl
issue on the Equals() method

9. Limitation : annotation @Beta
● Guava is mixture of frozen API and non frozen API
(marked with @Beta)
● See Guava documentation the list of non frozen API
● One new version each three months ?

10. Limitation : new functionality in
Java language
● Guava is maybe more interesting for old version of Java
(java7) than in last version Java8
● Example integration of Optional in Java8

11. Reasons to use Guava
● Collection Initializers and Utilities
● Limited Functional-Style Programming
● Multimap and Bimaps
● Easy Hashcodes and Comparators
● Defensive Coding

12. Reasons to use Guava : Guava vs
Commons
● Apache commons and Guava have some similar features
but ...
● Apache Commons
– Mature library (almost 10 years)
– Target java 1.4 (Commons 3.0 java 1.5+)
● Guava
– Well designed and documented
– Target java6+
– Guava is still in active development

13. Example : simple in-memory cache
● Quiz 2
– How to create a simple cache ?

14. Example : simple in-memory cache
● Two types of cache
– Loading cache (the interresting one)
– Cache
● Simple in-memory cache
– Thread safe
– Simple eviction strategy

15. Example : simple in-memory cache
public CacheLoader<String,String> loader = new
CacheLoader<String,String>() {
public String load(String key) {
return key.toUpperCase();
}
};
public LoadingCache<String, String> cache = CacheBuilder
.newBuilder()
.build(loader);

16. Example : simple in-memory cache
public LoadingCache<String, String> cache CacheBuilder.newBuilder()
.maximumSize(size)
.recordStats()
.build(loader);
for(int i=0 ; i<1000; i++) {
myCache.cache.getUnchecked("simple test"+random10());
}
CacheStats stats = myCache.cache.stats();
stats.hitCount();
stats.missCount();

17. Example : Equals hash ... methods
● Class Person
– Attributs firstname, lastname, birthday...
– Methods :
● constructor,
● Equals/ hashCode / toString
● CompareTo

18. Example : Equals hash ... methods
● Class Person
– Attributs firstname, lastname, birthday...
– Methods :
● constructor,
● Equals/ hashCode / toString
● CompareTo

19. Example : Equals hash ... methods
●
Class PersonSimple
public int hasCode() {
final int prime = 31;
int result =1;
result = prime * result + ((birthday==null ? 0 : birthday.hashCode()));
result = prime * result + ((firstname==null ? 0 :
firstname.hashCode()));
result = prime * result + ((lastname==null ? 0 : lastname.hashCode()));
return result;
}

20. Example : Equals hash ... methods
● Class PersonWithGuava
public int hasCode() {
return Objects.hashCode(birthday, firstname,
lastname);
}

21. Example : Equals hash ... methods
Test with EclEmma comparison with and without Guava
PersonSimple PersonWithGuava
Constructor 58 instructions 42
equals 69 41
hashCode 45 19
toString 50 16
compareTo 28 18
Total instructions 238 136
Code coverage 84 % 90 %

22. Example : performance mesure
● Quiz 3
– How mesure the elapsed time
● Example one method/ a part of a method

23. Example : performance mesure
● Prefer Stopwatch
– over System.nanoTime
– and definitively over currentTimeMillis()
● Other solutions Jamon, java8 date API

24. Example : performance mesure
public static long longProcess() {
Stopwatch stopwatch = Stopwatch.createStarted();
subProcess1();
final long date2 = stopwatch.elapsed(TimeUnit.MILLISECONDS);
System.out.println("subprocess1 "+date2);
subProcess2();
final long date3 = stopwatch.elapsed(TimeUnit.MILLISECONDS);
System.out.println("subprocess1 "+(date3-date2));
return date3;
}

25. Conclusion
● When will you start with Guava ?