Hello, Guava !

What is Guava ?

The Guava project contains several of Google's core
libraries that we rely on in our Java-based projects:
collections, caching, primitives support, concurrency
libraries, common annotations, string processing, I/O,
and so forth.
http://code.google.com/p/guava-libraries/

GoogleによるJavaライブラリ

Guaaaaaaaaaaaaaaaaaaaava!
2 Copyright © 2012 Akira Koyasu. Some rights reserved.

Guava provides...

•いつも書いている煩雑なコードを簡潔に書きやすく
•使い勝手の良いユーティリティクラス
•コンパクトなAPI

小さな悩みをすっきり解決。
あまり大きな悩みは解決してくれません。


How to use

Maven dependency

<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>11.0.2</version>
</dependency>

... or Use other dependency managements,
Download jar from the site


Packages
com.google.common.annotations
com.google.common.base
com.google.common.cache
com.google.common.collect
com.google.common.eventbus
com.google.common.hash
com.google.common.io
com.google.common.math
com.google.common.net
com.google.common.primitives
com.google.common.util.concurrent



Subject 0.

プログラムの実行時間を測りましょう

Subject 1.

コストの高い処理の結果をキャッシュしましょう


大切なインタフェース

Function<F,T>
T apply(F input)

Predicate<T>
boolean apply(T input)

Supplier<T>
T get()


Preconditions

import static com.google.common.base.Preconditions.*;
...
public void someMethod(int pos) {
checkArgument(pos > 0);
}

posが0以下の場合はIllegalArgumentExceptionが
スローされます


Joiner

String[] strs = { "taro", "jiro", "saburo" };
String str = Joiner.on(",").join(strs);

Splitter

String str = "taro,jiro,saburo";
Iterable<String> strs = Splitter.on(",").split(str);


CaseFormat

LOWER_HYPHEN
LOWER_UNDERSCORE
LOWER_CAMEL
UPPER_CAMEL
UPPER_UNDERSCORE

import static com.google.common.base.CaseFormat.*;

LOWER_UNDERSCORE.to(LOWER_CAMEL, "create_date"); // createDate
UPPER_CAMEL.to(LOWER_UNDERSCORE, "SomeName"); // some_name


Stopwatch

Stopwatch stopwatch = new Stopwatch().start();
stopwatch.stop();
System.out.printf("time: %s%n", stopwatch);

Charsets

Charset charset = Charsets.UTF_8;



Subject 2.

あるリストを加工して別のリストを作りましょう


頻出メソッド

Collection<E> filter(Collection<E> unfiltered,
Predicate<? super E> predicate)

Collection<T> transform(Collection<F> fromCollection,
Function<? super F,T> function)


Lists

List<String> list1 = Lists.newArrayList();
List<String> list2
= Lists.newArrayListWithCapacity(100);

Maps

Map<Integer, String> map1 = Maps.newHashMap();
Map<Integer, String> map2
= Maps.newHashMapWithExpectedSize(100);


ForwardingCollection
List<String> list = new ForwardingList<String>() {
@Override
protected List<String> delegate() {
return backingList;
}
};

ImmutableCollection
ImmutableSet<String> set
=ImmutableSet.<String>builder()
.add("taro")
.add("jiro")
.add("saburo").build();


ComparisonChain

public class SomeOne implements Comparable<SomeOne> {
private String name;
private int age;

@Override
public int compareTo(SomeOne that) {
return ComparisonChain.start()
.compare(this.age, that.age)
.compare(this.name, that.name)
.result();
}
}


Range

Range<Integer> range1 = Ranges.closed(1, 10);
range1.apply(10); // true

Range<Integer> range2 = Ranges.open(1, 10);
range2.apply(10); // false


@Beta



Subject 3.

ファイルの内容を標準出力へ出力しましょう


ByteStreams

static long copy(InputStream from, OutputStream to)

static byte[] toByteArray(InputStream in)

CharStreams

static long copy(Readable from, Appendable to)

static String toString(Readable r)


Files

static void touch(File file)

static void copy(File from, File to)

static void move(File from, File to)

static BufferedReader newReader(File file, Charset charset)

static BufferedWriter newWriter(File file, Charset charset)


Resources

URL url = Resources.getResource(Sample.class, "test.txt");
try {
String str = Resources.toString(url, Charsets.UTF_8);
System.out.println(str);
} catch (IOException e) {
e.printStackTrace();
}

これはなんとなく微妙・・・変わるかもしれません


Conclusion


Conclusion

Google + Java = Guava

今日から使えるライブラリ
コンパクトなAPI＝学習コスト低
開発効率は劇的に向上

Happy programming with Guava!!


Notes

This work is licensed under the Creative Commons Attribution-
NonCommercial 3.0 Unported License. To view a copy of this
license, visit http://creativecommons.org/licenses/by-nc/3.0/.

Page1 photo from:
http://www.ﬂickr.com/photos/hermansaksono/4297175782/


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