Guava 是java api的增强与扩展，提供复杂的java 数据结构，使你的代码更简短精炼，具有良好的可读性。看看guava给我们提供了哪些很酷的功能:
Map<String, Map<String, String>> map = Maps.newHashMap(); List<List<Map<String, String>>> list = Lists.newArrayList();
Set<String> set = Sets.newHashSet("one","two","three");
List<String> list = Lists.newArrayList("one","two","three");
ImmutableSet<String> immutableSet = ImmutableSet.of("RED", "GREEN");
从构造的方式来说，ImmutableSet 集合还提供了 Builder 模式来构造一个集合 :
Builder<String> builder = ImmutableSet.builder();
ImmutableSet<String> immutableSet = builder.add("RED").addAll(set).build();
Multimap<String, Person> customersByType =ArrayListMultimap.create();
customersByType.put("abc", new Person(1, 1, "a", "46546", 1, 20));
customersByType.put("abc", new Person(1, 1, "a", "46546", 1, 30));
Multiset<Integer> multiSet = HashMultiset.create(); multiSet.add(10); multiSet.add(30); multiSet.add(30); multiSet.add(40); System.out.println( multiSet.count(30)); // 2 System.out.println( multiSet.size()); //4
Table<Integer,Integer,Person> personTable=HashBasedTable.create(); personTable.put(1,20,new Person(1, 1, "a", "46546", 1, 20)); personTable.put(0,30,new Person(2, 1, "ab", "46546", 0, 30)); // 得到行集合 Map<Integer,Person> rowMap= personTable.row(0); int maxAge= Collections.max(rowMap.keySet());
//双向map
BiMap<Integer,String> biMap=HashBiMap.create();
biMap.put(1,"hello");
biMap.put(2,"my");
int value= biMap.inverse().get("my");
ClassToInstanceMap<Person> classToInstanceMap =MutableClassToInstanceMap.create(); classToInstanceMap.putInstance(Person.class, new Person(1,20,"abc","46464",1,100)); Person person = classToInstanceMap.getInstance(Person.class);
Collections2.filter(personList,new Predicate<Person>() {
@Override
public boolean apply( Person input) {
return input.getSex()==0;
}
})
同时可以转换一个集合为另外一个集合：
Lists.transform(personList,new Function<Person, String>() {
@Override
public String apply( Person input) {
return input.getName();
}
})
ConcurrentMap<String, Object> mapAll = new MapMaker()
.concurrencyLevel(8)
.softKeys()
.weakValues()
.expireAfterWrite(30, TimeUnit.SECONDS)
.maximumSize(100)
.makeComputingMap(
new Function<String, Object>() {
public Object apply(String key) {
return createObject(key);
}});
Lists.newArrayList(30, 20, 60, 80, 10); Ordering.natural().sortedCopy(numbers); //10,20,30,60,80 Ordering.natural().reverse().sortedCopy(numbers); //80,60,30,20,10 Ordering.natural().min(numbers); //10 Ordering.natural().max(numbers); //80 Lists.newArrayList(30, 20, 60, 80, null, 10); Ordering.natural().nullsLast().sortedCopy(numbers); //10, 20,30,60,80,null Ordering.natural().nullsFirst().sortedCopy(numbers); //null,10,20,30,60,80
List<Person> personList=Lists.newArrayList(
new Person(3, 1, "abc", "46546", 0, 25),
new Person(2, 1, "ab", "46546", 0, 30),
new Person(5, 1, "ade", "46546",0, 27)
);
Ordering<Person> byAge = new Ordering<Person>() {
@Override
public int compare( Person left, Person right) {
return right.getAge()-left.getAge();
}
};
for(Person p: byAge.immutableSortedCopy(personList))
{
System.out.println(p);
}
// 使用ComparisonChain比较多字段
Collections.sort(list, new Comparator<Foo>(){
@Override
return ComparisonChain.start()
.compare(f1.a, f2.a, comparatorA)
.compare(f1.b, f2.b, comparatorB)
.compare(f1.c, f2.c, comparatorC).result();
}});
maven坐标：
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>14.0-rc2</version>
</dependency>
对于开发人员来说，Guava 确实是一把利器，封装了许多实用的API，让我们编写代码更简单易读，这篇文章是我学习Guava的总结，希望大家能从中有所收获。
原文：http://www.cnblogs.com/diegodu/p/6119749.html