# 4-函数式编程
# 4-函数式编程
[原文链接](http://code.google.com/p/guava-libraries/wiki/FunctionalExplained) [译文链接](http://ifeve.com/google-guava-functional) 译者：沈义扬，校对：丁一
## 注意事项
截至JDK7，Java中也只能通过笨拙冗长的匿名类来达到近似函数式编程的效果。预计JDK8中会有所改变，但Guava现在就想给JDK5以上用户提供这类支持。
过度使用Guava函数式编程会导致冗长、混乱、可读性差而且低效的代码。这是迄今为止最容易（也是最经常）被滥用的部分，如果你想通过函数式风格达成一行代码，致使这行代码长到荒唐，Guava团队会泪流满面。
比较如下代码：
```
<pre class="calibre11">```
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);
}
};
Multiset<Integer> lengths = HashMultiset.create(
Iterables.transform(Iterables.filter(strings, allCaps), lengthFunction));
```
```
或FluentIterable的版本
```
<pre class="calibre11">```
Multiset<Integer> lengths = HashMultiset.create(
FluentIterable.from(strings)
.filter(new Predicate<String>() {
public boolean apply(String string) {
return CharMatcher.JAVA_UPPER_CASE.matchesAllOf(string);
}
})
.transform(new Function<String, Integer>() {
public Integer apply(String string) {
return string.length();
}
}));
```
```
还有
```
<pre class="calibre11">```
Multiset<Integer> lengths = HashMultiset.create();
for (String string : strings) {
if (CharMatcher.JAVA_UPPER_CASE.matchesAllOf(string)) {
lengths.add(string.length());
}
}
```
```
即使用了静态导入，甚至把Function和Predicate的声明放到别的文件，第一种代码实现仍然不简洁，可读性差并且效率较低。
截至JDK7，命令式代码仍应是默认和第一选择。不应该随便使用函数式风格，除非你绝对确定以下两点之一：
- 使用函数式风格以后，整个工程的代码行会净减少。在上面的例子中，函数式版本用了11行， 命令式代码用了6行，把函数的定义放到另一个文件或常量中，并不能帮助减少总代码行。
- 为了提高效率，转换集合的结果需要懒视图，而不是明确计算过的集合。此外，确保你已经阅读和重读了Effective Java的第55条，并且除了阅读本章后面的说明，你还真正做了性能测试并且有测试数据来证明函数式版本更快。
请务必确保，当使用Guava函数式的时候，用传统的命令式做同样的事情不会更具可读性。尝试把代码写下来，看看它是不是真的那么糟糕？会不会比你想尝试的极其笨拙的函数式 更具可读性。
## Functions\[函数\]和Predicates\[断言\]
本节只讨论直接与Function和Predicate打交道的Guava功能。一些其他工具类也和”函数式风格”相关，例如[`Iterables.concat(Iterable<Iterable>)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#concat%28java.lang.Iterable%29)，和其他用常量时间返回视图的方法。尝试看看[2.3节的集合工具类](http://ifeve.com/google-guava-collectionutilities)。
Guava提供两个基本的函数式接口：
- Function<A, B>，它声明了单个方法B apply(A input)。Function对象通常被预期为引用透明的——没有副作用——并且引用透明性中的”相等”语义与equals一致，如a.equals(b)意味着function.apply(a).equals(function.apply(b))。
- Predicate<T>，它声明了单个方法boolean apply(T input)。Predicate对象通常也被预期为无副作用函数，并且”相等”语义与equals一致。
### 特殊的断言
字符类型有自己特定版本的Predicate——[`CharMatcher`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/base/CharMatcher.html)，它通常更高效，并且在某些需求方面更有用。CharMatcher实现了Predicate<Character>，可以当作Predicate一样使用，要把Predicate转成CharMatcher，可以使用[`CharMatcher.forPredicate`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6common/base/CharMatcher.html#forPredicate%28com.google.common.base.Predicate%29)。更多细节请参考第6章-字符串处理。
此外，对可比较类型和基于比较逻辑的Predicate，Range类可以满足大多数需求——它表示一个不可变区间。Range类实现了Predicate，用以判断值是否在区间内。例如，Range.atMost(2)就是个完全合法的Predicate<Integer>。更多使用Range的细节请参照第8章。
### 操作Functions和Predicates
[Functions](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/base/Functions.html)提供简便的Function构造和操作方法，包括：
[`forMap(Map<A, B>)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Functions.html#forMap%28java.util.Map%29)[`compose(Function<B, C>, Function<A, B>)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Functions.html#compose%28com.google.common.base.Function,%20com.google.common.base.Function%29)[`constant(T)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Functions.html#constant%28E%29)[`identity()`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Functions.html#identity%28%29)[`toStringFunction()`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Functions.html#toStringFunction%28%29)细节请参考Javadoc。
相应地，[Predicates](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/base/Predicates.html)提供了更多构造和处理Predicate的方法，下面是一些例子：
[`instanceOf(Class)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#instanceOf%28java.lang.Class%29)[`assignableFrom(Class)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#assignableFrom%28java.lang.Class%29)[`contains(Pattern)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#contains%28java.util.regex.Pattern%29)[`in(Collection)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#in%28java.util.Collection%29)[`isNull()`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#isNull%28%29)[`alwaysFalse()`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#alwaysFalse%28%29)[`alwaysTrue()`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#alwaysTrue%28%29)[`equalTo(Object)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#equalTo%28T%29)[`compose(Predicate, Function)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#compose%28com.google.common.base.Predicate,%20com.google.common.base.Function%29)[`and(Predicate...)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#and%28com.google.common.base.Predicate...%29)[`or(Predicate...)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#or%28com.google.common.base.Predicate...%29)[`not(Predicate)`](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#not%28com.google.common.base.Predicate%29)细节请参考Javadoc。
## 使用函数式编程
Guava提供了很多工具方法，以便用Function或Predicate操作集合。这些方法通常可以在集合工具类找到，如Iterables，Lists，Sets，Maps，Multimaps等。
### 断言
断言的最基本应用就是过滤集合。所有Guava过滤方法都返回”视图”——*译者注：即并非用一个新的集合表示过滤，而只是基于原集合的视图*。
**集合类型****过滤方法**Iterable[`Iterables.filter(Iterable, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#filter%28java.lang.Iterable,%20com.google.common.base.Predicate%29)[`FluentIterable.filter(Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release12/javadoc/co%E2%80%A6common/collect/FluentIterable.html#filter%28com.google.common.base.Predicate%29)Iterator[`Iterators.filter(Iterator, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#filter%28java.util.Iterator,%20com.google.common.base.Predicate%29)Collection[`Collections2.filter(Collection, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Collections2.html#filter%28java.util.Collection,%20com.google.common.base.Predicate%29)Set[`Sets.filter(Set, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Sets.html#filter%28java.util.Set,%20com.google.common.base.Predicate%29)SortedSet[`Sets.filter(SortedSet, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Sets.html#filter%28java.util.SortedSet,%20com.google.common.base.Predicate%29)Map[`Maps.filterKeys(Map, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#filterKeys%28java.util.Map,%20com.google.common.base.Predicate%29)[`Maps.filterValues(Map, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#filterValues%28java.util.Map,%20com.google.common.base.Predicate%29)[`Maps.filterEntries(Map, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#filterEntries%28java.util.Map,%20com.google.common.base.Predicate%29)SortedMap[`Maps.filterKeys(SortedMap, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#filterKeys%28java.util.SortedMap,%20com.google.common.base.Predicate%29)[`Maps.filterValues(SortedMap, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#filterValues%28java.util.SortedMap,%20com.google.common.base.Predicate%29)[`Maps.filterEntries(SortedMap, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#filterEntries%28java.util.SortedMap,%20com.google.common.base.Predicate%29)Multimap[`Multimaps.filterKeys(Multimap, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6ommon/collect/Multimaps.html#filterKeys%28com.google.common.collect.Multimap,%20com.google.common.base.Predicate%29)[`Multimaps.filterValues(Multimap, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6mon/collect/Multimaps.html#filterValues%28com.google.common.collect.Multimap,%20com.google.common.base.Predicate%29)[`Multimaps.filterEntries(Multimap, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6on/collect/Multimaps.html#filterEntries%28com.google.common.collect.Multimap,%20com.google.common.base.Predicate%29)\*List的过滤视图被省略了，因为不能有效地支持类似get(int)的操作。请改用Lists.newArrayList(Collections2.filter(list, predicate))做拷贝过滤。
除了简单过滤，Guava另外提供了若干用Predicate处理Iterable的工具——通常在[`Iterables`](http://docs.guava-libraries.googlecode.com/git-history/release12/javadoc/com/google/common/collect/Iterables.html)工具类中，或者是[`FluentIterable`](http://docs.guava-libraries.googlecode.com/git-history/release12/javadoc/com/google/common/collect/FluentIterable.html)的”fluent”（链式调用）方法。
**Iterables\*\***方法签名\*\***说明****另请参见**[`boolean all(Iterable, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#all%28java.lang.Iterable,%20com.google.common.base.Predicate%29)是否所有元素满足断言？懒实现：如果发现有元素不满足，不会继续迭代[`Iterators.all(Iterator, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#all%28java.util.Iterator,%20com.google.common.base.Predicate%29)[`FluentIterable.allMatch(Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release12/javadoc/co%E2%80%A6mmon/collect/FluentIterable.html#allMatch%28com.google.common.base.Predicate%29)[`boolean any(Iterable, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#any%28java.lang.Iterable,%20com.google.common.base.Predicate%29)是否有任意元素满足元素满足断言？懒实现：只会迭代到发现满足的元素[`Iterators.any(Iterator, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#any%28java.util.Iterator,%20com.google.common.base.Predicate%29)[`FluentIterable.anyMatch(Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release12/javadoc/co%E2%80%A6mmon/collect/FluentIterable.html#anyMatch%28com.google.common.base.Predicate%29)[`T find(Iterable, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#find%28java.lang.Iterable,%20com.google.common.base.Predicate%29)循环并返回**一个**满足元素满足断言的元素，如果没有则抛出NoSuchElementException[`Iterators.find(Iterator, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#find%28java.util.Iterator,%20com.google.common.base.Predicate%29) [`Iterables.find(Iterable, Predicate, T default)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#find%28java.lang.Iterable,%20com.google.common.base.Predicate,%20T%29) [`Iterators.find(Iterator, Predicate, T default)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#find%28java.util.Iterator,%20com.google.common.base.Predicate,%20T%29)[`Optional<T> tryFind(Iterable, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#tryFind%28java.lang.Iterable,%20com.google.common.base.Predicate%29)返回**一个**满足元素满足断言的元素，若没有则返回`O`ptional.absent()[`Iterators.find(Iterator, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#find%28java.util.Iterator,%20com.google.common.base.Predicate%29) [`Iterables.find(Iterable, Predicate, T default)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#find%28java.lang.Iterable,%20com.google.common.base.Predicate,%20T%29) [`Iterators.find(Iterator, Predicate, T default)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#find%28java.util.Iterator,%20com.google.common.base.Predicate,%20T%29)[`indexOf(Iterable, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#indexOf%28java.lang.Iterable,%20com.google.common.base.Predicate%29)返回第一个满足元素满足断言的元素索引值，若没有返回-1[`Iterators.indexOf(Iterator, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#indexOf%28java.util.Iterator,%20com.google.common.base.Predicate%29)[`removeIf(Iterable, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#removeIf%28java.lang.Iterable,%20com.google.common.base.Predicate%29)移除所有满足元素满足断言的元素，实际调用Iterator.remove()方法[`Iterators.removeIf(Iterator, Predicate)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#removeIf%28java.util.Iterator,%20com.google.common.base.Predicate%29)### 函数
到目前为止，函数最常见的用途为转换集合。同样，所有的Guava转换方法也返回原集合的视图。
**集合类型****转换\*\***方法\*\*Iterable[`Iterables.transform(Iterable, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterables.html#transform%28java.lang.Iterable,%20com.google.common.base.Function%29)[`FluentIterable.transform(Function)`](http://docs.guava-libraries.googlecode.com/git-history/release12/javadoc/co%E2%80%A6mmon/collect/FluentIterable.html#transform%28com.google.common.base.Function%29)Iterator[`Iterators.transform(Iterator, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Iterators.html#transform%28java.util.Iterator,%20com.google.common.base.Function%29)Collection[`Collections2.transform(Collection, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Collections2.html#transform%28java.util.Collection,%20com.google.common.base.Function%29)List[`Lists.transform(List, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Lists.html#transform%28java.util.List,%20com.google.common.base.Function%29)Map\*[`Maps.transformValues(Map, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#transformValues%28java.util.Map,%20com.google.common.base.Function%29)[`Maps.transformEntries(Map, EntryTransformer)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#transformEntries%28java.util.Map,%20com.google.common.collect.Maps.EntryTransformer%29)SortedMap\*[`Maps.transformValues(SortedMap, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#transformValues%28java.util.SortedMap,%20com.google.common.base.Function%29)[`Maps.transformEntries(SortedMap, EntryTransformer)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#transformEntries%28java.util.SortedMap,%20com.google.common.collect.Maps.EntryTransformer%29)Multimap\*[`Multimaps.transformValues(Multimap, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6/collect/Multimaps.html#transformValues%28com.google.common.collect.Multimap,%20com.google.common.base.Function%29)[`Multimaps.transformEntries(Multimap, EntryTransformer)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6collect/Multimaps.html#transformEntries%28com.google.common.collect.Multimap,%20com.google.common.collect.Maps.EntryTransformer%29)ListMultimap\*[`Multimaps.transformValues(ListMultimap, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6lect/Multimaps.html#transformValues%28com.google.common.collect.ListMultimap,%20com.google.common.base.Function%29)[`Multimaps.transformEntries(ListMultimap, EntryTransformer)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6ect/Multimaps.html#transformEntries%28com.google.common.collect.ListMultimap,%20com.google.common.collect.Maps.EntryTransformer%29)Table[`Tables.transformValues(Table, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6common/collect/Tables.html#transformValues%28com.google.common.collect.Table,%20com.google.common.base.Function%29)\*Map和[`Multimap`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Multimap.html)有特殊的方法，其中有个[`EntryTransformer<K, V1, V2>`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.EntryTransformer.html)参数，它可以使用旧的键值来计算，并且用计算结果替换旧值。
\*对Set的转换操作被省略了，因为不能有效支持contains(Object)操作——*译者注：懒视图实际上不会全部计算转换后的**Set**元素，因此不能高效地支持**contains(Object)**。*请改用Sets.newHashSet(Collections2.transform(set, function))进行拷贝转换。
```
<pre class="calibre11">```
List<String> names;
Map<String, Person> personWithName;
List<Person> people = Lists.transform(names, Functions.forMap(personWithName));
ListMultimap<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;
}
});
```
```
可以组合Function使用的类包括：
Ordering[`Ordering.onResultOf(Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6le/common/collect/Ordering.html#onResultOf%28com.google.common.base.Function%29)Predicate[`Predicates.compose(Predicate, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/base/Predicates.html#compose%28com.google.common.base.Predicate,%20com.google.common.base.Function%29)Equivalence[`Equivalence.onResultOf(Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6le/common/base/Equivalence.html#onResultOf%28com.google.common.base.Function%29)Supplier[`Suppliers.compose(Function, Supplier)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/base/Suppliers.html#compose%28com.google.common.base.Function,%20com.google.common.base.Supplier%29)Function[`Functions.compose(Function, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/base/Functions.html#compose%28com.google.common.base.Function,%20com.google.common.base.Function%29)此外，[ListenableFuture](http://code.google.com/p/guava-libraries/wiki/ListenableFutureExplained) API支持转换ListenableFuture。Futures也提供了接受[`AsyncFunction`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/util/concurrent/AsyncFunction.html)参数的方法。AsyncFunction是Function的变种，它允许异步计算值。
[`Futures.transform(ListenableFuture, Function)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6/Futures.html#transform%28com.google.common.util.concurrent.ListenableFuture,%20com.google.common.base.Function%29)[`Futures.transform(ListenableFuture, Function, Executor)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6/Futures.html#transform%28com.google.common.util.concurrent.ListenableFuture,%20com.google.common.base.Function,%20java.util.concurrent.Executor%29)[`Futures.transform(ListenableFuture, AsyncFunction)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6/Futures.html#transform%28com.google.common.util.concurrent.ListenableFuture,%20com.google.common.util.concurrent.AsyncFunction%29)[`Futures.transform(ListenableFuture, AsyncFunction, Executor)`](http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/%E2%80%A6/Futures.html#transform%28com.google.common.util.concurrent.ListenableFuture,%20com.google.common.util.concurrent.AsyncFunction,%20java.util.concurrent.Executor%29)
- 介紹
- Google Guava官方教程（中文版）
- 1-基本工具
- 1.1-使用和避免null
- 1.2-前置条件
- 1.3-常见Object方法
- 1.4-排序: Guava强大的”流畅风格比较器”
- 1.5-Throwables：简化异常和错误的传播与检查
- 2-集合
- 2.1-不可变集合
- 2.2-新集合类型
- 2.3-强大的集合工具类：java.util.Collections中未包含的集合工具
- 2.4-集合扩展工具类
- 3-缓存
- 4-函数式编程
- 5-并发
- 5.1-google Guava包的ListenableFuture解析
- 5.2-Google-Guava Concurrent包里的Service框架浅析
- 6-字符串处理：分割，连接，填充
- 7-原生类型
- 9-I/O
- 10-散列
- 11-事件总线
- 12-数学运算
- 13-反射