Cleaner code with Guava

08-02-2012

@mitemitreski

Code samples @ git://github.com/mitemitreski/guava-examples.git

What is Guava?

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

NULL

"Null sucks." - Doug Lea

"I call it my billion-dollar mistake." - C. A. R. Hoare

if ( x != null && x.someM()!=null && ) {}

Null is ambiguous

@Test

public void optionalExample() {

Optional<Integer> possible = Optional.of(3);// Make optional of given type

possible.isPresent(); // returns true if nonNull

possible.or(10); // returns this possible value or default

possible.get(); // returns 3

}

@Test

public void testNeverNullWithoutGuava() {

Integer defaultId = null;

Integer id = theUnknowMan.getId() != null ? theUnknowMan.getId() : defaultId;

}

@Test(expected = NullPointerException.class)

public void testNeverNullWithGuava() {

Integer defaultId = null;

int id = Objects.firstNonNull(theUnknowMan.getId(), defaultId);

assertEquals(0, id);

}

// all in (expression, format,message)

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());

}

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

What to use and when?

Eclipse support

hashCode() and equals()

@Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((adress == null) ? 0 : adress.hashCode()); result = prime * result + ((id == null) ? 0 : id.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); result = prime * result + ((url == null) ? 0 : url.hashCode()); return result; }

hashCode() and equals()

@Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((adress == null) ? 0 : adress.hashCode()); result = prime * result + ((id == null) ? 0 : id.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); result = prime * result + ((url == null) ? 0 : url.hashCode()); return result; }

The Guava way

Objects.equal("a", "a"); //returns trueObjects.equal(null, "a"); //returns falseObjects.equal("a", null); //returns falseObjects.equal(null, null); //returns true

Object.equals(Object a, Object b)

Object.deepEquals(Object a, Object b)

JDK7

Objects.hashCode(name,adress,url);

Objects.hash(name,adress,url);

 Objects.toStringHelper(this)       .add("x", 1)       .toString();

The Guava way

public int compareTo(Foo that) {     return ComparisonChain.start()         .compare(this.aString, that.aString)         .compare(this.anInt, that.anInt)         .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())         .result();   }

Common Primitives

Joiner/ Splitter

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'))

Character Matchers

String noControl = CharMatcher.JAVA_ISO_CONTROL.removeFrom(string); // remove control charactersString theDigits = CharMatcher.DIGIT.retainFrom(string); // only the digitsString lowerAndDigit = CharMatcher.or(CharMatcher.JAVA_DIGIT, CharMatcher.JAVA_LOWER_CASE).retainFrom(string);  // eliminate all characters that aren't digits or lowercase

import com.google.common.cache.*;

Cache<Integer, Customer> cache = CacheBuilder.newBuilder() .weakKeys() .maximumSize(10000) .expireAfterWrite(10, TimeUnit.MINUTES) .build(new CacheLoader<Integer, Customer>() {

@Override public Customer load(Integer key) throws Exception {

return retreveCustomerForKey(key); }

});

import 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.)

Functions and Predicates

Java 8 will support closures …

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);  }};

It is not recommended to overuse this!!!

Filter collections

@Test public void filterAwayNullMapValues() { SortedMap<String, String> map = new TreeMap<String, String>(); map.put("1", "one"); map.put("2", "two"); map.put("3", null); map.put("4", "four"); SortedMap<String, String> filtered = SortedMaps.filterValues(map, Predicates.notNull()); assertThat(filtered.size(), is(3)); // null entry for "3" is gone! }

Filter collectionsCollection type Filter method

Iterable Iterables.filter(Iterable, Predicate)

Iterator Iterators.filter(Iterator, Predicate)

Collection Collections2.filter(Collection, Predicate)

Set Sets.filter(Set, Predicate)

SortedSet Sets.filter(SortedSet, Predicate)

Map Maps.filterKeys(Map, Predicate) Maps.filterValues(Map, Predicate)Maps.filterEntries(Map, Predicate)

SortedMap Maps.filterKeys(SortedMap, Predicate)Maps.filterValues(SortedMap, Predicate)Maps.filterEntries(SortedMap, Predicate)

Multimap Multimaps.filterKeys(Multimap, Predicate)Multimaps.filterValues(Multimap, Predicate)Multimaps.filterEntries(Multimap, Predicate)

Iterables Signature

boolean all(Iterable, Predicate)

boolean any(Iterable, Predicate)

T find(Iterable, Predicate)

removeIf(Iterable, Predicate)

Transform collectionsListMultimap<String, String> firstNameToLastNames;// maps first names to all last names of people with that first name

ListMultimap<String, String> firstNameToName = Multimaps.transformEntries(firstNameToLastNames,  new EntryTransformer<String, String, String> () {    public String transformEntry(String firstName, String lastName) {      return firstName + " " + lastName;    }  });

Transform collections

Collection type Transform method

Iterable Iterables.transform(Iterable, Function)

Iterator Iterators.transform(Iterator, Function)

Collection Collections2.transform(Collection, Function)

List Lists.transform(List, Function)

Map* Maps.transformValues(Map, Function) Maps.transformEntries(Map, EntryTransformer)

SortedMap* Maps.transformValues(SortedMap, Function)Maps.transformEntries(SortedMap, EntryTransformer)

Multimap* Multimaps.transformValues(Multimap, Function)Multimaps.transformEntries(Multimap, EntryTransformer)

ListMultimap* Multimaps.transformValues(ListMultimap, Function)

Multimaps.transformEntries(ListMultimap, EntryTransformer)

Table Tables.transformValues(Table, Function)

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> map = ImmutableMap.of("key1", "value1", "key2", "value2"); //list of ints List<Integer> theList = Ints.asList(1, 2, 3, 4, 522, 5, 6);

Load resources

When to use Guava?

• Temporary collections

• Mutable collections

• String Utils

• Check if (x==null)

• Always ?

When to use 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 for You

•When you use a popular library, your code is in the

mainstream

•When you find an improvement to your private library, how

many people did you help?

Well argued in Effective Java 2e, Item 47.

Where can you use it ?

•Java 5.0+

• GWT

•Android

<dependency>    <groupId>com.google.guava</groupId>    <artifactId>guava</artifactId>    <version>10.0.1</version></dependency>