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Guava by Example
(Google's Core Libraries for Java)
Etienne Neveu
04/03/2011
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Base
com.google.common.base
Collections
com.google.common.collect
Functional programming
Miscellaneous
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Base
com.google.common.base
Collections
com.google.common.collect
Functional programming
Miscellaneous
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Base – Simple example bean
public class Employee {
private String name;
private Integer age;
private Job job;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public Job getJob() {
return job;
}
public void setJob(Job job) {
this.job = job;
}
}
public enum Job {
CEO,
DEVELOPER,
DESIGNER
}
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Base – Objects.equal()
public class Employee {
private String name;
private Integer age;
private Job job;
}
public boolean equals(Object object) {
if (!(object instanceof Employee)) return false;
Employee that = (Employee) object;
return (name == that.name || (name != null && name.equals(that.name)))
&& (age == that.age || (age != null && age.equals(that.age)))
&& job == that.job;
}
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Base – Objects.equal()
public class Employee {
private String name;
private Integer age;
private Job job;
}
public boolean equals(Object object) {
if (!(object instanceof Employee)) return false;
Employee that = (Employee) object;
return (name == that.name || (name != null && name.equals(that.name)))
&& (age == that.age || (age != null && age.equals(that.age)))
&& job == that.job;
}
public boolean equals(Object object) {
if (!(object instanceof Employee)) return false;
Employee that = (Employee) object;
return Objects.equal(name, that.name)
&& Objects.equal(age, that.age)
&& job == that.job;
}
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Base – Objects.hashCode()
public class Employee {
private String name;
private Integer age;
private Job job;
}
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (age != null ? age.hashCode() : 0);
result = 31 * result + (job != null ? job.hashCode() : 0);
return result;
}
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Base – Objects.hashCode()
public class Employee {
private String name;
private Integer age;
private Job job;
}
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (age != null ? age.hashCode() : 0);
result = 31 * result + (job != null ? job.hashCode() : 0);
return result;
}
public int hashCode() {
return Objects.hashCode(name, age, job);
}
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Base – Objects.toStringHelper()
public class Employee {
private String name;
private Integer age;
private Job job;
}
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append(Employee.class.getSimpleName());
sb.append("{name=").append(name);
sb.append(", age=").append(age);
sb.append(", job=").append(job);
sb.append('}');
return sb.toString();
}
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Base – Objects.toStringHelper()
public class Employee {
private String name;
private Integer age;
private Job job;
}
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append(Employee.class.getSimpleName());
sb.append("{name=").append(name);
sb.append(", age=").append(age);
sb.append(", job=").append(job);
sb.append('}');
return sb.toString();
}
public String toString() {
return Objects.toStringHelper(this)
.add("name", name)
.add("age", age)
.add("job", job)
.toString();
}
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Base – ComparisonChain
public class Employee {
private String name;
private Integer age;
private Job job;
}
public int compareTo(Employee other) {
int result = name.compareTo(other.name);
if (result != 0) return result;
result = age.compareTo(other.age);
if (result != 0) return result;
return job.compareTo(other.job);
}
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Base – ComparisonChain
public class Employee {
private String name;
private Integer age;
private Job job;
}
public int compareTo(Employee other) {
int result = name.compareTo(other.name);
if (result != 0) return result;
result = age.compareTo(other.age);
if (result != 0) return result;
return job.compareTo(other.job);
}
public int compareTo(Employee other) {
return ComparisonChain.start()
.compare(name, other.name)
.compare(age, other.age)
.compare(job, other.job)
.result();
}
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Base – ComparisonChain & Ordering
public class Employee {
private String name;
private Integer age;
private Job job;
}
public int compareTo(Employee other) {
int result = name.compareTo(other.name);
if (result != 0) return result;
result = age.compareTo(other.age);
if (result != 0) return result;
return job.compareTo(other.job);
}
public int compareTo(Employee other) {
return ComparisonChain.start()
.compare(name, other.name, Ordering.natural().nullsLast())
.compare(age, other.age, Ordering.natural().reverse().nullsLast())
.compare(job, other.job, Ordering.natural().nullsLast())
.result();
}
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Base – Preconditions
public class Money {
private final BigDecimal amount;
private final Currency currency;
public Money(BigDecimal amount, Currency currency) {
if (amount == null) {
throw new NullPointerException("amount must not be null");
}
if (currency == null) {
throw new NullPointerException("currency must not be null");
}
if (amount.signum() < 0) {
throw new IllegalArgumentException("amount must be positive: " + amount);
}
this.amount = amount;
this.currency = currency;
}
}
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Base – Preconditions
import com.google.common.base.Preconditions;
public class Money {
private final BigDecimal amount;
private final Currency currency;
public Money(BigDecimal amount, Currency currency) {
Preconditions.checkNotNull(amount, "amount must not be null");
Preconditions.checkNotNull(currency, "currency must not be null");
Preconditions.checkArgument(amount.signum() >= 0, "amount must be positive: %s", amount);
this.amount = amount;
this.currency = currency;
}
}
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Base – Preconditions
import com.google.common.base.Preconditions;
public class Money {
private final BigDecimal amount;
private final Currency currency;
public Money(BigDecimal amount, Currency currency) {
this.amount = Preconditions.checkNotNull(amount, "amount must not be null");
this.currency = Preconditions.checkNotNull(currency, "currency must not be null");
Preconditions.checkArgument(amount.signum() >= 0, "amount must be positive: %s", amount);
}
}
public static T checkNotNull(T reference) {
if (reference == null) {
throw new NullPointerException();
}
return reference;
}
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Base – Preconditions
import static com.google.common.base.Preconditions.*;
public class Money {
private final BigDecimal amount;
private final Currency currency;
public Money(BigDecimal amount, Currency currency) {
this.amount = checkNotNull(amount, "amount must not be null");
this.currency = checkNotNull(currency, "currency must not be null");
checkArgument(amount.signum() >= 0, "amount must be positive: %s", amount);
}
}
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Base – Preconditions
import static com.google.common.base.Preconditions.*;
public class Money {
private final BigDecimal amount;
private final Currency currency;
public Money(BigDecimal amount, Currency currency) {
this.amount = checkNotNull(amount, "amount must not be null");
this.currency = checkNotNull(currency, "currency must not be null");
checkArgument(amount.signum() >= 0, "amount must be positive: %s", amount);
}
}
More information:
http://stackoverflow.com/questions/3128120/what-is-the-proper-error-message-to-supply-to-google-guavas-preconditions
http://piotrjagielski.com/blog/google-guava-vs-apache-commons-for-argument-validation/
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Base – Objects.firstNonNull()
private static final String UNKNOWN_COORDINATES = "Unknown coordinates";
public String getCoordinatesAsText() {
return getGpsCoordinates() != null ? getGpsCoordinates() : UNKNOWN_COORDINATES;
}
public String getGpsCoordinates() {
// retrieve GPS coordinates from satellite
}
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Base – Objects.firstNonNull()
private static final String UNKNOWN_COORDINATES = "Unknown coordinates";
public String getCoordinatesAsText() {
return getGpsCoordinates() != null ? getGpsCoordinates() : UNKNOWN_COORDINATES;
}
public String getGpsCoordinates() {
// retrieve GPS coordinates from satellite → SLOW!
}
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Base – Objects.firstNonNull()
private static final String UNKNOWN_COORDINATES = "Unknown coordinates";
public String getCoordinatesAsText() {
String gpsCoordinates = getGpsCoordinates();
return gpsCoordinates != null ? gpsCoordinates : UNKNOWN_COORDINATES;
}
public String getGpsCoordinates() {
// retrieve GPS coordinates from satellite
}
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Base – Objects.firstNonNull()
private static final String UNKNOWN_COORDINATES = "Unknown coordinates";
public String getCoordinatesAsText() {
return Objects.firstNonNull(getGpsCoordinates(), UNKNOWN_COORDINATES);
}
public String getGpsCoordinates() {
// retrieve GPS coordinates from satellite
}
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Base – Joiner
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", "Chuck Norris");
String names = Joiner.on(", ").join(heroes);
// "Kick-Ass, Iron Man, Chuck Norris"
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Base – Joiner
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", "Chuck Norris");
String names = Joiner.on(", ").join(heroes);
// "Kick-Ass, Iron Man, Chuck Norris"
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", null, "Chuck Norris");
String names = Joiner.on(", ").join(heroes);
// throws NullPointerException
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Base – Joiner
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", "Chuck Norris");
String names = Joiner.on(", ").join(heroes);
// "Kick-Ass, Iron Man, Chuck Norris"
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", null, "Chuck Norris");
String names = Joiner.on(", ").join(heroes);
// throws NullPointerException
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", null, "Chuck Norris");
String names = Joiner.on(", ").skipNulls().join(heroes);
// "Kick-Ass, Iron Man, Chuck Norris"
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Base – Joiner
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", "Chuck Norris");
String names = Joiner.on(", ").join(heroes);
// "Kick-Ass, Iron Man, Chuck Norris"
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", null, "Chuck Norris");
String names = Joiner.on(", ").join(heroes);
// throws NullPointerException
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", null, "Chuck Norris");
String names = Joiner.on(", ").skipNulls().join(heroes);
// "Kick-Ass, Iron Man, Chuck Norris"
List heroes = Lists.newArrayList("Kick-Ass", "Iron Man", null, "Chuck Norris");
String names = Joiner.on(", ").useForNull("Invisible Man").join(heroes);
// prints "Kick-Ass, Iron Man, Invisible Man, Chuck Norris"
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Base – Joiner (MapJoiner)
Map map = new HashMap();
map.put(1, "Chuck Norris");
map.put(2, "Iron Man");
map.put(3, "Kick-Ass");
String ranks = Joiner.on('\n').withKeyValueSeparator(" -> ").join(map);
System.out.println(ranks);
Prints:
1 -> Chuck Norris
2 -> Iron Man
3 -> Kick-Ass
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Base – CharMatcher
We want to accept: 0 1 2 3 4 5 6 7 8 9 - _
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Base – CharMatcher
We want to accept: 0 1 2 3 4 5 6 7 8 9 - _
private static final CharMatcher VALID_CHARS = CharMatcher.DIGIT.or(CharMatcher.anyOf(“-_”);
String VALID_CHARS.retainFrom(input);
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Base – CharMatcher
We want to accept: 0 1 2 3 4 5 6 7 8 9 - _
private static final CharMatcher VALID_CHARS = CharMatcher.DIGIT.or(CharMatcher.anyOf(“-_”);
String VALID_CHARS.retainFrom(input);
Import static com.google.common.base.Preconditions.*;
checkArgument(CharMatcher.WHITESPACE.matchesAllOf(input));
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Base – CharMatcher
We want to accept: 0 1 2 3 4 5 6 7 8 9 - _
private static final CharMatcher VALID_CHARS = CharMatcher.DIGIT.or(CharMatcher.anyOf(“-_”);
String VALID_CHARS.retainFrom(input);
Import static com.google.common.base.Preconditions.*;
checkArgument(CharMatcher.WHITESPACE.matchesAllOf(input));
String decoded = decode(base64encodedString);
--> problem: decoded String is padded with NULL control characters
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Base – CharMatcher
We want to accept: 0 1 2 3 4 5 6 7 8 9 - _
private static final CharMatcher VALID_CHARS = CharMatcher.DIGIT.or(CharMatcher.anyOf(“-_”);
String VALID_CHARS.retainFrom(input);
Import static com.google.common.base.Preconditions.*;
checkArgument(!CharMatcher.WHITESPACE.matchesAllOf(input));
String decoded = decode(base64encodedString);
--> problem: decoded String is padded with NULL control characters
String result = CharMatcher.JAVA_CONTROL_CHAR.trimTrailingFrom(decoded);
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Base – Splitter
Iterable heroes = Splitter.on(“,”).split(“Iron Man, , Kick-Ass,Didier Girard”);
// contains “Iron Man”, “ “, “ Kick-Ass”, “Didier Girard”
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Base – Splitter
Iterable heroes = Splitter.on(“,”).split(“Iron Man, , Kick-Ass,Didier Girard”);
// contains “Iron Man”, “ “, “ Kick-Ass”, “Didier Girard”
Iterable heroes = Splitter.on(“,”).trimResults().split(“Iron Man, , Kick-Ass,Didier Girard”);
// contains “Iron Man”, ““, “Kick-Ass”, “Didier Girard”
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Base – Splitter
Iterable heroes = Splitter.on(“,”).split(“Iron Man, , Kick-Ass,Didier Girard”);
// contains “Iron Man”, “ “, “ Kick-Ass”, “Didier Girard”
Iterable heroes = Splitter.on(“,”).trimResults().split(“Iron Man, , Kick-Ass,Didier Girard”);
// contains “Iron Man”, ““, “Kick-Ass”, “Didier Girard”
Iterable heroes = Splitter.on(“,”).trimResults().omitEmptyStrings()
.split(“Iron Man, , Kick-Ass,Didier Girard”);
// contains “Iron Man”, “Kick-Ass”, “Didier Girard”
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Base
com.google.common.base
Collections
com.google.common.collect
Functional programming
Miscellaneous
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Collections – Static factories
// standard ArrayList
List> maps = new ArrayList>();
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Collections – Static factories
// standard ArrayList
List> maps = new ArrayList>();
// type inference using Guava static factory
List> maps = Lists.newArrayList();
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Collections – Static factories
// standard ArrayList
List> maps = new ArrayList>();
// type inference using Guava static factory
List> maps = Lists.newArrayList();
// another static factory (good naming conventions)
List names = Lists.newArrayListWithExpectedSize(42);
List names = Lists.newArrayListWithCapacity(42);
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Collections – Static factories
// standard ArrayList
List> maps = new ArrayList>();
// type inference using Guava static factory
List> maps = Lists.newArrayList();
// another static factory (good naming conventions)
List names = Lists.newArrayListWithExpectedSize(42);
List names = Lists.newArrayListWithCapacity(42);
// from var args
List names = Lists.newArrayList("Tony Stark", "James Rhodes");
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Collections – Static factories
// standard ArrayList
List> maps = new ArrayList>();
// type inference using Guava static factory
List> maps = Lists.newArrayList();
// another static factory (good naming conventions)
List names = Lists.newArrayListWithExpectedSize(42);
List names = Lists.newArrayListWithCapacity(42);
// from var args
List names = Lists.newArrayList("Tony Stark", "James Rhodes");
// from Iterable
Iterable namesIterable = …
List names = Lists.newArrayList(namesIterable);
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Collections – Static factories
// standard ArrayList
List> maps = new ArrayList>();
// type inference using Guava static factory
List> maps = Lists.newArrayList();
// another static factory (good naming conventions)
List names = Lists.newArrayListWithExpectedSize(42);
List names = Lists.newArrayListWithCapacity(42);
// from var args
List names = Lists.newArrayList("Tony Stark", "James Rhodes");
// from Iterable
Iterable namesIterable = …
List names = Lists.newArrayList(namesIterable);
// Sets
Set employees = Sets.newHashSet();
// Maps
Map employeesById = Maps.newHashMapWithExpectedSize(5);
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Collections – Static factories
import static com.google.common.collect.Lists.*;
import static com.google.common.collect.Maps.newHashMapWithExpectedSize;
import static com.google.common.collect.Sets.newHashSet;
// type inference using Guava static factory
List> maps = newArrayList();
// another static factory (good naming conventions)
List names = newArrayListWithExpectedSize(42);
List names = newArrayListWithCapacity(42);
// from var args
List names = newArrayList("Tony Stark", "James Rhodes");
// from Iterable
Iterable namesIterable = …
List names = newArrayList(namesIterable);
// Sets
Set employees = newHashSet();
// Maps
Map employeesById = newHashMapWithExpectedSize(5);
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Collections – Immutable collections
public static final Set LOCALES =
Collections.unmodifiableSet(
new LinkedHashSet(
Arrays.asList(Locale.FRANCE, Locale.JAPAN, Locale.GERMAN)
)
);
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Collections – Immutable collections
public static final Set LOCALES =
Collections.unmodifiableSet(
new LinkedHashSet(
Arrays.asList(Locale.FRANCE, Locale.JAPAN, Locale.GERMAN)
)
);
public static final Set LOCALES =
ImmutableSet.of(Locale.FRANCE, Locale.JAPAN, Locale.GERMAN);
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Collections – Immutable collections
public static final Map LOCALE_RANKS;
static {
Map ranks = new LinkedHashMap();
ranks.put(Locale.GERMAN, 1);
ranks.put(Locale.FRANCE, 2);
ranks.put(Locale.JAPAN, 3);
LOCALE_RANKS = Collections.unmodifiableMap(ranks);
}
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Collections – Immutable collections
public static final Map LOCALE_RANKS;
static {
Map ranks = new LinkedHashMap();
ranks.put(Locale.GERMAN, 1);
ranks.put(Locale.FRANCE, 2);
ranks.put(Locale.JAPAN, 3);
LOCALE_RANKS = Collections.unmodifiableMap(ranks);
}
public static final Map LOCALE_RANKS;
static {
ImmutableMap.Builder ranks = ImmutableMap.builder();
ranks.put(Locale.GERMAN, 1);
ranks.put(Locale.FRANCE, 2);
ranks.put(Locale.JAPAN, 3);
LOCALE_RANKS = ranks.build();
}
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Collections – Immutable collections
public static final Map LOCALE_RANKS;
static {
Map ranks = new LinkedHashMap();
ranks.put(Locale.GERMAN, 1);
ranks.put(Locale.FRANCE, 2);
ranks.put(Locale.JAPAN, 3);
LOCALE_RANKS = Collections.unmodifiableMap(ranks);
}
public static final Map LOCALE_RANKS;
static {
ImmutableMap.Builder ranks = ImmutableMap.builder();
ranks.put(Locale.GERMAN, 1);
ranks.put(Locale.FRANCE, 2);
ranks.put(Locale.JAPAN, 3);
LOCALE_RANKS = ranks.build();
}
public static final Map LOCALE_RANKS =
ImmutableMap.builder()
.put(Locale.GERMAN, 1)
.put(Locale.FRANCE, 2)
.put(Locale.JAPAN, 3)
.build();
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Collections – Immutable collections
public static final Map LOCALE_RANKS;
static {
Map ranks = new LinkedHashMap();
ranks.put(Locale.GERMAN, 1);
ranks.put(Locale.FRANCE, 2);
ranks.put(Locale.JAPAN, 3);
LOCALE_RANKS = Collections.unmodifiableMap(ranks);
}
public static final Map LOCALE_RANKS =
ImmutableMap.of(Locale.GERMAN, 1,
Locale.FRANCE, 2,
Locale.JAPAN, 3);
public static ImmutableMap of()
public static ImmutableMap of(K k1, V v1)
public static ImmutableMap of(K k1, V v1, K k2, V v2)
public static ImmutableMap of(K k1, V v1, K k2, V v2, K k3, V v3)
public static ImmutableMap of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4)
public static ImmutableMap of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5)
public static Builder builder()
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Collections – Immutable collections
ImmutableCollection
ImmutableList
ImmutableSet
ImmutableMap
ImmutableSortedSet
...
ImmutableMultimap
ImmutableBiMap
ImmutableMultiset
ImmutableClassToInstanceMap
...
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Collections – Immutable collections
Avantages
✔
Concurrent programming
✔
Clarity / simplicity
✔
Performance
✔
Programming errors detected early (fail fast)
✔
Defensive copying is un-needed
✔
Null-hostile
Caveats
✔
Not deeply
deeply immutable if elements are mutable
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Collections – BiMap
public enum MilitaryRank {
GENERAL,
SOLDIER,
NINJA;
}
public interface RankConverter {
MilitaryRank toMilitaryRank(Job job);
Job toJob(MilitaryRank rank);
}
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Collections – BiMap
public class RankConverterUsingSwitches implements RankConverter {
public MilitaryRank toMilitaryRank(Job job) {
switch (job) {
case CEO:
return MilitaryRank.GENERAL;
case DEVELOPER:
return MilitaryRank.SOLDIER;
case DESIGNER:
return MilitaryRank.NINJA;
default:
return null;
}
}
public Job toJob(MilitaryRank rank) {
switch (rank) {
case GENERAL:
return Job.CEO;
case SOLDIER:
return Job.DEVELOPER;
case NINJA:
return Job.DESIGNER;
default:
return null;
}
}
}
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Collections – BiMap
public class RankConverterUsingTwoMaps implements RankConverter {
private Map jobToRank = Maps.newHashMap();
private Map rankToJob = Maps.newHashMap();
{
putInBothMaps(Job.CEO, MilitaryRank.GENERAL);
putInBothMaps(Job.DEVELOPER, MilitaryRank.NINJA);
putInBothMaps(Job.DESIGNER, MilitaryRank.NINJA);
}
private void putInBothMaps(Job job, MilitaryRank rank) {
jobToRank.put(job, rank);
rankToJob.put(rank, job);
}
public MilitaryRank toMilitaryRank(Job job) {
return jobToRank.get(job);
}
public Job toJob(MilitaryRank rank) {
return rankToJob.get(rank);
}
}
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Collections – BiMap
public class RankConverterUsingTwoMaps implements RankConverter {
private Map jobToRank = Maps.newHashMap();
private Map rankToJob = Maps.newHashMap();
{
putInBothMaps(Job.CEO, MilitaryRank.GENERAL);
putInBothMaps(Job.DEVELOPER, MilitaryRank.NINJA);
putInBothMaps(Job.DESIGNER, MilitaryRank.NINJA);
}
private void putInBothMaps(Job job, MilitaryRank rank) {
jobToRank.put(job, rank);
rankToJob.put(rank, job);
}
public MilitaryRank toMilitaryRank(Job job) {
return jobToRank.get(job);
}
public Job toJob(MilitaryRank rank) {
return rankToJob.get(rank);
}
}
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Collections – BiMap
public class RankConverterUsingBiMap implements RankConverter {
private BiMap jobToRank = EnumBiMap.create(ImmutableMap.of(
Job.CEO, MilitaryRank.GENERAL,
Job.DEVELOPER, MilitaryRank.NINJA,
Job.DESIGNER, MilitaryRank.NINJA
));
@Override
public MilitaryRank toMilitaryRank(Job job) {
return jobToRank.get(job);
}
@Override
public Job toJob(MilitaryRank rank) {
return jobToRank.inverse().get(rank);
}
}
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Collections – BiMap
public class RankConverterUsingBiMap implements RankConverter {
private BiMap jobToRank = EnumBiMap.create(ImmutableMap.of(
Job.CEO, MilitaryRank.GENERAL,
Job.DEVELOPER, MilitaryRank.NINJA,
Job.DESIGNER, MilitaryRank.NINJA
));
@Override
public MilitaryRank toMilitaryRank(Job job) {
return jobToRank.get(job);
}
@Override
public Job toJob(MilitaryRank rank) {
return jobToRank.inverse().get(rank);
}
}
java.lang.IllegalArgumentException: value already present: NINJA
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:115)
at com.google.common.collect.AbstractBiMap.putInBothMaps(AbstractBiMap.java:111)
at com.google.common.collect.AbstractBiMap.put(AbstractBiMap.java:96)
at com.google.common.collect.AbstractBiMap.putAll(AbstractBiMap.java:144)
at com.google.common.collect.EnumBiMap.putAll(EnumBiMap.java:38)
at com.google.common.collect.EnumBiMap.create(EnumBiMap.java:69)
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Collections – BiMap
public class RankConverterUsingBiMap implements RankConverter {
private BiMap jobToRank = EnumBiMap.create(ImmutableMap.of(
Job.CEO, MilitaryRank.GENERAL,
Job.DEVELOPER, MilitaryRank.SOLDIER,
Job.DESIGNER, MilitaryRank.NINJA
));
@Override
public MilitaryRank toMilitaryRank(Job job) {
return jobToRank.get(job);
}
@Override
public Job toJob(MilitaryRank rank) {
return jobToRank.inverse().get(rank);
}
}
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Collections – Multimap
Map> getEmployeesPerJob(List employees) {
Map> map = Maps.newHashMap();
for (Employee employee : employees) {
addToMap(map, employee.getJob(), employee);
}
return map;
}
void addToMap(Map> map, Job job, Employee employee) {
Collection employeesForJob = map.get(job);
if (employeesForJob == null) {
employeesForJob = Lists.newArrayList();
map.put(job, employeesForJob);
}
employeesForJob.add(employee);
}
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Collections – Multimap
Map> getEmployeesPerJob(List employees) {
Map> map = Maps.newHashMap();
for (Employee employee : employees) {
addToMap(map, employee.getJob(), employee);
}
return map;
}
void addToMap(Map> map, Job job, Employee employee) {
Collection employeesForJob = map.get(job);
if (employeesForJob == null) {
employeesForJob = Lists.newArrayList();
map.put(job, employeesForJob);
}
employeesForJob.add(employee);
}
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Collections – Multimap
Map> getEmployeesPerJob(List employees) {
Multimap multimap = ArrayListMultimap.create();
for (Employee employee : employees) {
multimap.put(employee.getJob(), employee);
}
return multimap.asMap();
}
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Base
com.google.common.base
Collections
com.google.common.collect
Functional programming
Miscellaneous
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Functional Programming – Interfaces
public interface Function {
T apply(@Nullable F input);
}
public interface Predicate {
boolean apply(@Nullable T input);
}
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Functional Programming – Interfaces
public class EmployeeNameFunction implements Function {
@Override
public String apply(Employee employee) {
return employee.getName();
}
}
public class EmployeeJobPredicate implements Predicate {
private final Job job;
public EmployeeJobPredicate(Job job) {
this.job = job;
}
@Override
public boolean apply(Employee employee) {
return employee.getJob() == job;
}
}
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Functional Programming – filter() / transform()
List getDesignerNames(List employees) {
List names = new ArrayList();
for (Employee employee : employees) {
if (employee.getJob() == Job.DESIGNER) {
names.add(employee.getName());
}
}
return names;
}
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Functional Programming – filter() / transform()
List getDesignerNames(List employees) {
Iterable designers = Iterables.filter(employees,
new Predicate() {
@Override
public boolean apply(Employee employee) {
return employee.getJob() == Job.DESIGNER;
}
}
);
Iterable names = Iterables.transform(designers,
new Function() {
@Override
public String apply(Employee employee) {
return employee.getName();
}
}
);
return ImmutableList.copyOf(names);
}
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Functional Programming – filter() / transform()
List getDesignerNames(List employees) {
Iterable designers = Iterables.filter(employees,
new EmployeeJobPredicate(Job.DESIGNER));
Iterable names = Iterables.transform(designers, new EmployeeNameFunction());
return ImmutableList.copyOf(names);
}
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Functional Programming – Best Practices
public final class EmployeePredicates {
private EmployeePredicates() {}
public static Predicate hasJob(Job job) {
return new EmployeeJobPredicate(job);
}
private static class EmployeeJobPredicate implements Predicate {
final Job job;
EmployeeJobPredicate(Job job) {
this.job = job;
}
@Override
public boolean apply(Employee employee) {
return employee.getJob() == job;
}
}
}
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Functional Programming – Best Practices
public final class EmployeeFunctions {
private EmployeeFunctions() {}
public static Function getName() {
return EmployeeNameFunction.INSTANCE;
}
private static class EmployeeNameFunction implements Function {
static final EmployeeNameFunction INSTANCE = new EmployeeNameFunction();
@Override
public String apply(Employee employee) {
return employee.getName();
}
}
}
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Functional Programming – Best Practices
public final class EmployeeFunctions {
private EmployeeFunctions() {}
public static Function getName() {
return EmployeeNameFunction.INSTANCE;
}
private enum EmployeeNameFunction implements Function {
INSTANCE;
@Override
public String apply(Employee employee) {
return employee.getName();
}
}
}
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Functional Programming – Best Practices
List getDesignerNames(List employees) {
Iterable designers = Iterables.filter(employees,
EmployeePredicates.hasJob(Job.DESIGNER));
Iterable names = Iterables.transform(designers, EmployeeFunctions.getName());
return ImmutableList.copyOf(names);
}
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Functional Programming – Predicate composition
List getDesignerNames(List employees) {
List designerNames = new ArrayList();
for (Employee employee : employees) {
if (employee != null && employee.getJob() == Job.DESIGNER) {
designerNames.add(employee.getName());
}
}
return designerNames;
}
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Functional Programming – Predicate composition
List getDesignerNames(List employees) {
Iterable designers = Iterables.filter(employees,
Predicates.and(
Predicates.notNull(),
EmployeePredicates.hasJob(Job.DESIGNER))
);
Iterable names = Iterables.transform(designers, EmployeeFunctions.getName());
return ImmutableList.copyOf(names);
}
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Functional Programming – Predicate composition
public final class EmployeePredicates {
private EmployeePredicates() {}
public static Predicate hasJob(Job job) {
return Predicates.compose(
Predicates.equalTo(job),
EmployeeFunctions.getJob());
}
}
public final class EmployeeFunctions {
[...]
public static Function getJob() {
return EmployeeJobFunction.INSTANCE;
}
private enum EmployeeJobFunction implements Function {
INSTANCE;
@Override
public Job apply(Employee employee) {
return employee.getJob();
}
}
}
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Functional Programming – Multimaps.index()
Map> getEmployeesPerJob(List employees) {
Multimap multimap = ArrayListMultimap.create();
for (Employee employee : employees) {
multimap.put(employee.getJob(), employee);
}
return multimap.asMap();
}
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Functional Programming – Multimaps.index()
Map> getEmployeesPerJob(List employees) {
ImmutableListMultimap multimap = Multimaps.index(employees,
EmployeeFunctions.getJob());
return multimap.asMap();
}
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Base
com.google.common.base
Collections
com.google.common.collect
Functional programming
Miscellaneous
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Miscellaneous – Charsets
byte[] bytes;
try {
bytes = string.getBytes("UTF-8");
} catch (UnsupportedEncodingException e) {
// how can this possibly happen?
throw new AssertionError(e);
}
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Miscellaneous – Charsets
byte[] bytes;
try {
bytes = string.getBytes("UTF-8");
} catch (UnsupportedEncodingException e) {
// how can this possibly happen?
throw new AssertionError(e);
}
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Miscellaneous – Charsets
byte[] bytes;
try {
bytes = string.getBytes("UTF-8");
} catch (UnsupportedEncodingException e) {
// how can this possibly package happen?
throw new AssertionError(e);
}
import com.google.common.base.Charsets;
[...]
byte[] bytes = string.getBytes(Charsets.UTF_8);
http://stackoverflow.com/questions/1684040/java-why-charset-names-are-not-constants
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Miscellaneous – I/O
public List readLines(File file) throws IOException {
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader(file));
} catch (FileNotFoundException ex) {
throw new RuntimeException(ex);
}
try {
List result = Lists.newArrayList();
while (true) {
String line = reader.readLine();
if (line == null) {
break;
}
result.add(line.trim());
}
return result;
} finally {
reader.close();
}
}
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Miscellaneous – I/O
public List readLines(File file) throws IOException {
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader(file));
} catch (FileNotFoundException ex) {
throw new RuntimeException(ex);
}
try {
List result = Lists.newArrayList();
while (true) {
String line = reader.readLine();
if (line == null) {
break;
}
result.add(line.trim());
}
return result;
} finally {
reader.close();
}
}
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Miscellaneous – I/O
import com.google.common.io.Files;
public List readLines(File file) throws IOException {
return Files.readLines(file, Charsets.UTF_8);
}
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Miscellaneous – I/O
import com.google.common.io.Files;
public List readLines(File file) throws IOException {
return Files.readLines(file, Charsets.UTF_8);
}
✔
Files.move()
✔
Files.copy()
✔
Files.touch()
✔
Files.createTempDir()
●
...
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Miscellaneous – @VisibleForTesting
public List getFemaleHeroes() {
List heroes = getAllHeroes();
return filterHeroesBySex(heroes, Sex.FEMALE);
}
private List filterHeroesBySex(List heroes, Sex sex) {
return ImmutableList.copyOf(Iterables.filter(heroes, new SexPredicate(sex)));
}
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Miscellaneous – @VisibleForTesting
public List getFemaleHeroes() {
List heroes = getAllHeroes();
return filterHeroesBySex(heroes, Sex.FEMALE);
}
private List filterHeroesBySex(List heroes, Sex sex) {
return ImmutableList.copyOf(Iterables.filter(heroes, new SexPredicate(sex)));
}
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Miscellaneous – @VisibleForTesting
public List getFemaleHeroes() {
List heroes = getAllHeroes();
return filterHeroesBySex(heroes, Sex.FEMALE);
}
private List filterHeroesBySex(List heroes, Sex sex) {
return ImmutableList.copyOf(Iterables.filter(heroes, new SexPredicate(sex)));
}
public List getFemaleHeroes() {
List heroes = getAllHeroes();
return filterHeroesBySex(heroes, Sex.FEMALE);
}
@VisibleForTesting
List filterHeroesBySex(List heroes, Sex sex) {
return ImmutableList.copyOf(Iterables.filter(heroes, new SexPredicate(sex)));
}
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Miscellaneous – Ordering
final Comparator MARQUE_COMPARATOR = new Comparator () {
static final Map RANK = new HashMap();
static {
RANK.put(Marque.SAMSUNG, 1);
RANK.put(Marque.HTC, 2);
RANK.put(Marque.APPLE, 3);
}
@Override
public int compare(Marque o1, Marque o2) {
Integer i1 = RANK.get(o1);
Integer i2 = RANK.get(o2);
if (i1 == null) { i1 = Integer.MAX_VALUE; }
if (i2 == null) { i2 = Integer.MAX_VALUE; }
return i1.compareTo(i2);
}
};
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Miscellaneous – Ordering
final Comparator MARQUE_COMPARATOR = new Comparator () {
static final Map RANK = new HashMap();
static {
RANK.put(Marque.SAMSUNG, 1);
RANK.put(Marque.HTC, 2);
RANK.put(Marque.APPLE, 3);
}
@Override
public int compare(Marque o1, Marque o2) {
Integer i1 = RANK.get(o1);
Integer i2 = RANK.get(o2);
if (i1 == null) { i1 = Integer.MAX_VALUE; }
if (i2 == null) { i2 = Integer.MAX_VALUE; }
return i1.compareTo(i2);
}
};
final Ordering MARQUE_ORDERING = Ordering.explicit(Marque.SAMSUNG,
Marque.HTC,
Marque.APPLE)
.nullsLast();
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Miscellaneous – Throwables
T doSomething() {
try {
return someMethodThatCouldThrowAnything();
} catch (IKnowWhatToDoWithThisException e) {
return handle(e);
} catch (Throwable t) {
throw Throwables.propagate(t);
}
}
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Miscellaneous – Resources
Official Website
http://code.google.com/p/guava-libraries/
StackOverflow
http://stackoverflow.com/questions/tagged/guava
Articles
http://codemunchies.com/tag/google-collections/
http://scaramoche.blogspot.com/search/label/guava
http://jnb.ociweb.com/jnb/jnbApr2010.html
Presentations at GTUG (August 2008 - some APIs may have changed)
http://www.youtube.com/watch?v=ZeO_J2OcHYM
http://www.youtube.com/watch?v=9ni_KEkHfto
PDF of a presentation given by Kevin Bourrillion, Guava's lead developer
http://guava-libraries.googlecode.com/files/Guava_for_Netflix_.pdf
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Recap
✔
Awesome library
✔
Very well maintained
✔
Supported on GWT / Android
✔
Performant
✔
Promotes good development practices
Also see http://stackoverflow.com/questions/4542550/what-are-the-big-improvements-between-guava-and-apache-equivalent-libraries
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Thanks!