1)Guava 简介
Guava 中文是石榴的意思，该项目是 Google 的一个开源项目，包含许多 Google 核心的 Java 常用库。
目前主要包含：
- com.google.common.annotations
- 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
在线API doc：http://www.osctools.net/apidocs/apidoc?api=guava
2)代码实现
package test;
import java.text.DecimalFormat;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.TimeUnit;
import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.collect.Collections2;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.HashMultiset;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.common.collect.MapMaker;
import com.google.common.collect.Ordering;
import com.google.common.collect.ImmutableSet.Builder;
/**
* @author gaozzsoft
*
*/
public class MyGuavaTest {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
List list = Lists.newArrayList();
//1 Immutable Collections: 真正的不可修改的集合
Set<String> set = new HashSet<String>(Arrays.asList(new String[]{"RED", "GREEN"}));
Set<String> unmodifiableSet = Collections.unmodifiableSet(set);
ImmutableSet<String> immutableSet = ImmutableSet.of("RED", "GREEN");
ImmutableSet<String> immutableSet2 = ImmutableSet.copyOf(set);
Builder<String> builder = ImmutableSet.builder();
ImmutableSet<String> immutableSet3 = builder.add("RED").addAll(set).build();
// Multiset: 把重复的元素放入集合
List<String> wordList =Arrays.asList(new String[]{"RED", "GREEN"});
Map<String, Integer> map = new HashMap<String, Integer>();
for(String word : wordList){
Integer count = map.get(word);
map.put(word, (count == null) ? 1 : count + 1);
}
//count word “RED”
Integer count = map.get("RED");
// Quit good method
HashMultiset<String> multiSet = HashMultiset.create();
multiSet.addAll(wordList);
//count word “RED”
Integer count2 = multiSet.count("RED");
//2 Multimap: 在 Map 的 value 里面放多个元素
//Key is candidate name, its value is his voters
HashMap<String, HashSet<String>> hMap = new HashMap<String, HashSet<String>>();
List<Ticket> tickets = Lists.newArrayList();
Ticket ticket1 = new Ticket("xijinping","gaozz");
Ticket ticket2 = new Ticket("xijinping","saiwg");
tickets.add(ticket1);
tickets.add(ticket2);
for(Ticket ticket: tickets){
HashSet<String> set2 = hMap.get(ticket.getCandidate());
if(set2 == null){
set2 = new HashSet<String>();
hMap.put(ticket.getCandidate(), set2);
}
set2.add(ticket.getVoter());
}
HashMultimap<String, String> map2 = HashMultimap.create();
for(Ticket ticket: tickets){
map2.put(ticket.getCandidate(), ticket.getVoter());
}
//3 BiMap: 双向 Map
// for(Map.Entry<User, Address> entry : map.entreSet()){
// if(entry.getValue().equals(anAddess)){
// return entry.getKey();
// }
// }
// return null;
// return biMap.inverse().get(anAddess);
// biMap == biMap.inverse().inverse();
//4 MapMaker: 超级强大的 Map 构造工具
//ConcurrentHashMap with concurrency level 8
ConcurrentMap<String, Object> map1 = new MapMaker()
.concurrencyLevel(8)
.makeMap();
//ConcurrentMap with soft reference key and weak reference value
ConcurrentMap<String, Object> map3 = new MapMaker()
.softKeys()
.weakValues()
.makeMap();
//Automatically removed entries from map after 30 seconds since they are created
ConcurrentMap<String, Object> map4 = new MapMaker()
.expireAfterWrite(30, TimeUnit.SECONDS)
.makeMap();
//Map size grows close to the 100, the map will evict
//entries that are less likely to be used again
ConcurrentMap<String, Object> map5 = new MapMaker()
.maximumSize(100)
.makeMap();
//Create an Object to the map, when get() is missing in map
ConcurrentMap<String, Object> map6 = new MapMaker()
.makeComputingMap(
new Function<String, Object>() {
public Object apply(String key) {
// return createObject(key);
return null;
}});
//Put all features together! 强大之处
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);
return null;
}});
//5 元素排序
//假设有个待排序的 List<Foo>，而 Foo 里面有两个排序关键字 int a, int b 和 int c
// Collections.sort(list, new Comparator<Foo>(){
// @Override
// public int compare(Foo f1, Foo f2) {
// int resultA = f1.a – f2.a;
// int resultB = f1.b – f2.b;
// return resultA == 0 ? (resultB == 0 ? f1.c – f2.c : resultB) : resultA;
//}});
// Collections.sort(list, new Comparator<Foo>(){
// @Override
// return ComparisonChain.start()
// .compare(f1.a, f2.a)
// .compare(f1.b, f2.b)
// .compare(f1.c, f2.c).result();
//}});
// Foo 里面每个排序关键字都已经有了各自的 Comparator，那么利用 ComparisonChain 可以
// 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();
// }});
//Ordring 类还提供了一个组合 Comparator 对象的方法
// 而且 Ordring 本身实现了 Comparator 接口所以它能直接作为 Comparator 使用
// Ordering<Foo> ordering = Ordering.compound(
// Arrays.asList(comparatorA, comparatorB, comparatorC));
// Collections.sort(list, ordering);
//6 过滤器&&转换器
//过滤器
Collection<Integer> filterCollection =
Collections2.filter(list, new Predicate<Integer>(){
// @Override
public boolean apply(Integer input) {
return input >= 10;
}});
//转换器
Set<Integer> setTmp = null;
Collection<String> formatCollection =
Collections2.transform(setTmp, new Function<Integer, String>(){
// @Override
public String apply(Integer input) {
return new DecimalFormat("#,###").format(input);
}} );
}
}